ASME Conference Presenter Attendance Policy and Archival Proceedings

2014;():V001T00A001. doi:10.1115/FuelCell2014-NS.

This online compilation of papers from the ASME 2014 12th International Conference on Fuel Cell Science, Engineering and Technology (FUELCELL2014) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

All Types of Electrolysis and Electrochemical Separation and Compression

2014;():V001T01A001. doi:10.1115/FuelCell2014-6510.

Today, industry has become more dependent on natural gases and combustion processes, creating a tremendous pressure to reduce their emissions. Although the current methods such as chemical looping combustion (CLC) and pure oxygen combustion have several advantages, there are still many limitations. A ceramic membrane based methane combustion reactor is an environmentally friendly technique for heat and power generation. This work investigates the performance of a perovskite-type SrSc0.1Co0.9O3−δ (SSC) membrane reactor for the catalytic combustion of methane. For this purpose, the mixed ionic and electronic conducting SSC oxygen-permeable planar membrane was prepared by a dry-pressing technique, and the SSC powder catalyst was spray coated on the permeation side of the membrane. Then, the prepared SSC membrane with the catalyst was used to perform the catalytic combustion of methane. The oxygen permeability of the membrane reactor was studied. Also, the methane conversion rates and CO2 selectivity at various test conditions were reported.

Commentary by Dr. Valentin Fuster
2014;():V001T01A002. doi:10.1115/FuelCell2014-6641.

This paper evaluates the potential for electrochemical hydrogen compression systems (EHCs) regarding their engineering performance, manufacturability, and capital costs. EHCs could enhance or replace mechanical hydrogen compressors. The physical embodiment of EHCs is similar to that of low temperature (LT) proton exchange membrane (PEM) fuel cell systems (FCSs). They also share common operating principles with LT PEM FCS and with PEM electrolysis systems. Design for Manufacturing and Assembly (DFMA™) analysis is applied to EHCs to identify manufactured designs, manufacturing methods, projected capital costs under mass-production, and cost drivers for both the EHC stack and the balance of plant (BOP). DFMA™ analysis reveals that EHC stack costs are expected to be roughly equal to EHC BOP costs, under a variety of scenarios. (Total EHC system costs are the sum of stack and BOP costs.) Within the BOP, the primary cost driver is the electrical power supply. Within the stack, the primary cost drivers include the membrane electrode assembly (MEA), the stamped bipolar plates, and the expanded titanium (Ti) cell supports, particularly at lower hydrogen outlet pressures. As outlet pressure rises, capital costs escalate nonlinearly for several reasons. Higher pressure EHCs experience higher mechanical loads, which necessitate using a greater number of smaller diameter cells and a greater tie rod mass. Higher pressure EHCs also exhibit a higher degree of back-diffusion, which necessitates using more cells per system.

Topics: Compression , Hydrogen
Commentary by Dr. Valentin Fuster

Design, Integration and Balance of Plant of Electrochemical Systems

2014;():V001T02A001. doi:10.1115/FuelCell2014-6330.

To evaluate the dynamic operation and feasibility of designing and operating a self-sustainable hydrogen fueling station using renewable energy sources, system models for a hydrogen fueling station using a proton exchange membrane (PEM) electrolyzer and fuel cell have been developed to simulate the renewable sources and fueling dynamics together with hydrogen production and station operation. Theoretical models have been integrated to simulate station performance when subjected to measured power and fueling demand dynamics from a public fueling station and measured renewable energy supply dynamics. The theoretical models that are integrated into various self-sustainable station design configurations include a Proton Exchange Membrane (PEM) electrolyzer and PEM fuel cell, hydrogen compressor, and storage tank. The fueling dynamics and power consumption dynamics were obtained from an operating public hydrogen fueling station and implemented in the system model. Various control strategies are simulated and the station performance is determined to depend upon the way renewable power is utilized in the station. Due to the round trip efficiency penalty associated with converting electricity to hydrogen (in an electrolyzer) and vice versa (in a fuel cell), the results suggest that the station operation power should be supplied by the renewable sources directly whenever possible, and that the hydrogen fuel cell should provide power only when there is no renewable power available (the third control strategy tested in this paper). The simulated hydrogen fueling station powered by 200 kW wind turbines or 360 kW solar PV were determined to successfully operate in a self-sustainable manner while dispensing ∼25 kg of hydrogen per day. This study provides insights regarding the sizing of the station components such as renewable energy conversion devices, electrolyzer and fuel cell, and storage tank. The cost of the hydrogen was determined to be $8.01 per kg when the station is powered by 200 kW of wind turbines and operated using control strategy 3, while it increased to $20.22 per kg when the station is powered by 360 kW of PV array and operated using control strategy 3. This study provides a basis for achieving self-sustainable renewable hydrogen fueling stations. With further optimization and development, these self-sustainable renewable hydrogen fueling stations could provide valuable interconnections (especially in remote locations) throughout the hydrogen infrastructure network and further support the integration of renewable sources for vehicle fuels.

Commentary by Dr. Valentin Fuster
2014;():V001T02A002. doi:10.1115/FuelCell2014-6331.

To improve the reliability and the energy efficiency of datacenters, as well as to reduce infrastructure costs and environmental impacts, we demonstrated and evaluated the use of a 10 kW Proton Exchange Membrane Fuel Cell (PEMFC) stack and system for powering the servers in a data center.

In this study, we designed, tested and demonstrated a PEMFC system as a Distributed Generation (DG) prime mover that has high reliability and efficiency for both steady state and dynamic operations. The 10kW PEMFC stack and system was designed to power a server rack and eliminate the power distribution system in the datacenter. The steady state electrical properties such as efficiency and polarization curves were evaluated. The ramp rate and dynamic response of the PEMFC system to server and system dynamics was also characterized and can be used to determine energy storage requirements and develop optimal control strategies to enable the dynamic load following capability.

Commentary by Dr. Valentin Fuster
2014;():V001T02A003. doi:10.1115/FuelCell2014-6375.

This study examines the successful development of a combustion-driven thermal transpiration-based combustor and a self-sustaining gas pump system having no moving parts and using readily storable hydrocarbon fuel. A stacked configuration was then integrated into the combustor creating a self-sustaining power generation system. In recent years, power generation devices employing hydrocarbon fuels rather than electrochemical storage as energy feedstock have been studied extensively due to the much higher energy densities of hydrocarbon fuels than the best available batteries. While many devices have been proposed including internal combustion engines and gas turbines, they all require the use of air to obtain a higher energy density so that only one reactant (fuel) need be carried. Thermal transpiration was accomplished by meeting two essential conditions: (1) gas flow in the transitional or molecular regime using glass microfiber filters as transpiration membranes and (2) a temperature gradient through the membrane using catalytic combustion downstream of the membrane. A cubic combustor was designed to house the thermal transpiration membrane and develop into a self-sustaining gas pump system. Fuel/Air would feed through an inlet into a mixing chamber that would flow into the thermal guard containing the thermal transpiration membrane. The thermal guard was developed from a high thermal conductivity stainless steel made into a cubic formation by using a 3D printing process. This configuration allowed both fuel and air to be transpired through the membrane meaning it was not possible for any reactant flow to occur as a result of the fuel supply pressure and only the membrane could draw reactants into the device.

In addition to pumping, a single-chamber solid-oxide fuel cell (SC-SOFC) was incorporated into combustion driven thermal transpiration pumps to convert chemical or thermal energy into electrical energy for a self-contained portable power generation system. Experiments showed that transpiration pumps with larger porosity and larger overall size exhibited better performance, though membrane pore size had little effect. These results were quantitatively consistent with theoretical predictions. By exploiting the temperature and fuel/oxygen concentrations within the transpiration pump, the SOFC achieved a maximum power density of 40 mW/cm2. Despite being far lower than necessary for a power source to be competitive with batteries, this preliminary study signifies an on-going positive efficiency that has potential for improvement through optimizing SOFC technology.

Commentary by Dr. Valentin Fuster
2014;():V001T02A004. doi:10.1115/FuelCell2014-6392.

Electrical energy storage (EES) is an important component of the future electric grid. Given that no other widely available technology meets all the EES requirements, reversible (or regenerative) solid oxide cells (ReSOCs) working in both fuel cell (power producing) and electrolysis (fuel producing) modes are envisioned as a technology capable of providing highly efficient and cost-effective EES. However, there are still many challenges from cell materials development to system level operation of ReSOCs that should be addressed before widespread application. One particular challenge of this novel system is establishing effective thermal management strategies to maintain the high conversion efficiency of the ReSOC. The system presented in this paper employs a thermal management strategy of promoting exothermic methanation in the ReSOC stack to offset the endothermic electrolysis reactions during charging mode (fuel producing) while also enhancing the energy density of the stored gases. Modeling and parametric analysis of an energy storage concept is performed using a thermodynamic system model coupled with a physically based ReSOC stack model. Results indicate that roundtrip efficiencies greater than 70% can be achieved at intermediate stack temperature (∼680°C) and pressure (∼20 bar). The optimal operating conditions result from a tradeoff between high stack efficiency and high parasitic balance of plant power.

Commentary by Dr. Valentin Fuster
2014;():V001T02A005. doi:10.1115/FuelCell2014-6488.

We have designed, built and tested a hydrogen fuel cell powered vehicle. The vehicle was constructed to specifications set forth for an international competition, which challenges high schools and universities to build and test energy efficient vehicles. We use a commercially available polymer exchange membrane (PEM) fuel cell system with a maximum output of 1.2 kW (1.6HP). The three-wheeled vehicle has a welded frame design utilizing aluminum square tubular components, an Ackermann steering system and an aerodynamically efficient hand-molded fiberglass body. A hub motor/controller powers the single rear wheel. Vehicle performance was determined in the laboratory. Performance curves for fuel consumption, torque and efficiency are presented. The vehicle successfully competed in the hydrogen fuel cell division of the competition.

Commentary by Dr. Valentin Fuster
2014;():V001T02A006. doi:10.1115/FuelCell2014-6489.

A one-dimensional model of a high-temperature solid-oxide fuel cell (SOFC) stack contained in a geothermic fuel cell (GFC) assembly is presented. The GFC concept, developed by IEP Technology Inc., involves the harnessing of heat generated during SOFC stack operation for the liberation of oil and gas from oil shale. The first GFC prototype, designed and built by Delphi Automotive, LLC., is comprised of three 1.5-kW SOFC stacks housed in a stainless-steel casing. Hot exhaust gases exiting the stacks are directed out of the stack-containment vessel, rejecting heat to the surroundings before being exhausted above ground. The primary aims of this work are to develop modeling tools to (1) predict the stack electrochemical performance and (2) elucidate the thermal characteristics of the stack assembly during operation through modeling and simulation. Aspen Plus process-simulation software and an embedded electrochemical model are utilized to predict the temperature dynamics and the electrical output of the GFC stack. The stack performance is decomposed with a temperature-dependent Area Specific Resistance (ASR) obtained from analysis of experimental data from a single stack that was operated over a wide temperature range. Independent full-scale stack testing has enabled performance validation of the electrochemical model. Experimental data from the three-stack GFC assembly has been used to calibrate the thermal-modeling approaches and the external heat-rejection predictions. Simulation results for steady-state conditions under hydrogen fuel are presented and compared to experimental data from thermocouples on the GFC prototype. The model will be used to explore the interaction of the geothermic fuel cell with the oil-shale formation in which it is installed.

Commentary by Dr. Valentin Fuster
2014;():V001T02A007. doi:10.1115/FuelCell2014-6522.

Solid oxide fuel cells (SOFCs) are a promising technology for clean power generation, however their implementation has been limited by several degradation mechanisms, which significantly reduce its lifetime under constant output power and inhibits the technology for commercialization in the near future. With the purpose of harnessing the capabilities offered by SOFCs, the U.S. DOE-National Energy Technology Laboratory (NETL) in Morgantown, WV has developed the Hybrid Performance (HyPer) project in which a SOFC 1D, real-time operating model is coupled to a gas turbine hardware system by utilizing hardware-in-the-loop simulation (HiLS).

More recently, in order to assess the long-term stability of the SOFC part of the system, electrochemical degradation due to operating conditions such as current density and fuel utilization have been incorporated into the SOFC model and successfully recreated in real time for standalone and hybrid operation. The mathematical expression for degradation rate was obtained through the analysis of empirical voltage versus time plots for different current densities and fuel utilizations at 750, 800, and 850°C. Simulation results well reflected the behavior of SOFC degradation rates from which the long-term stability of the cell under various conditions was assessed. Distributed fuel cell parameters are presented for both standalone and hybrid configurations. The incorporation of the electrochemical degradation rate into the SOFC model provides a framework to study more realistically Fuel Cell-hybrid systems and set forth a mechanism to improve the long-term stability of SOFCs through the hybridization of such technology.

Commentary by Dr. Valentin Fuster
2014;():V001T02A008. doi:10.1115/FuelCell2014-6523.

A pressure drop analysis for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior. It is possible to model, test and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and provide means of evaluating risk mitigation strategies.

The cold air bypass in the Hyper facility directs compressor discharge flow to the turbine inlet duct, bypassing the fuel cell and exhaust gas recuperators in the system. This valve reduces turbine inlet temperature while reducing cathode airflow, but significantly improves compressor surge margin. Regardless of the reduced turbine inlet temperature as the valve opens, a peak in turbine efficiency is observed during characterization of the valve at the middle of the operating range. A detailed experimental analysis shows the unusual behavior during steady state and transient operation, which is considered a key point for future control strategies in terms of turbine efficiency optimization and cathode airflow control.

Topics: Fuel cells , Turbines
Commentary by Dr. Valentin Fuster
2014;():V001T02A009. doi:10.1115/FuelCell2014-6547.

Previous studies have shown that the pseudo-bipolar design of the bi-cell is composed of two outside anodes and two inside cathodes that share a common PZT vibrating device used to pump the airflow. The bi-cell is operated by three modes of PZT-actuating process as pump mode (Pc > Pout > Pin), supply mode (Pout > Pin > Pc), and transition mode (Pout > Pc > Pin). In this study, a single module of piezoelectric PEMFC honey comb composed of 6 bi-cells on each inside wall of the honey comb has been developed to deliver the net power output 7.5W. The hydrogen storage tank is located in the middle duct of one honey comb with hydrogen supply valves and pipelines. Furthermore, for the required power output, the honey comb stack can be designed as erect-stack or planar-stack by assembling different number modules. Comparing with other polygons, the stronger honey comb stack can be designed to fit in the limited space and coupled with the fuel supply system or other power output system, for example, LED lights.

Commentary by Dr. Valentin Fuster
2014;():V001T02A010. doi:10.1115/FuelCell2014-6674.

A 300kW Solid Oxide Fuel Cell Gas Turbine (SOFC-GT) power plant simulator is evaluated with the use of a Model Reference Adaptive Control scheme, implemented for a set of nonlinear empirical Transfer Functions. The SOFC-GT simulator allows testing of various fuel cell models under a Hardware-in-the-Loop configuration that incorporates a 120kW Auxiliary Power Unit, and Balance-of-Plant components in hardware, and a fuel cell model in software. The adaptation technique is beneficial to plants having a wide range of operation, and strong coupling interaction. The practical implementation of the adaptive methodology is presented through simulation in the MATLAB/SIMULINK environment.

Commentary by Dr. Valentin Fuster
2014;():V001T02A011. doi:10.1115/FuelCell2014-6701.

Exhaust gas of internal combustion engine contains carbon-oxide and hydrocarbon. The temperature of these gases which are emitted in atmosphere are higher than 873 K. In the environment under the high-temperature gas. Reforming of Steam Methane Reforming, Water-Gas Shift Reaction and Carbon Precipitation are expected in the exhaust pipe. This environment of the exhaust-gases accommodates with operating environment of Solid Oxide Fuel Cell (SOFC). Therefore, if electricity can be collected from such exhaust gas environment, engine system can utilize smaller AC generator and battery, and if the gas reforming and electrochemical reactions can clean the exhaust gases, that can lead to disuse catalyzer. Those also can accomplish lighter engine system and totally efficiency of engine system.

Therefore, in order to collect electricity from exhaust gas, the single type SOFC unit is designed and installed in the exhaust pipe of 110cc engine of a small motorcycle. Various experiments are executed in this paper. The experimental results show that the developed SOFC-unit works, and power density of about 8.5mW/cm2 is obtained.

Commentary by Dr. Valentin Fuster
2014;():V001T02A012. doi:10.1115/FuelCell2014-6715.

Saint-Gobain has developed a unique all ceramic SOFC stack with performance characteristics that make it an attractive solution to the cost and durability challenges of commercializing conventional SOFCs. Saint-Gobain’s all ceramic stacks achieve power density higher than 200 mW/cm2 when operating at 800 °C and 0.75 V/cell. Power degradation is low at <0.2% per kilohour over more than 12,000 hours of testing. Ceramic interconnect stability is verified for >16,000 hours using accelerated testing. Good performance under thermal cycling, power cycling and unplanned transients such as fuel or air loss has also been confirmed. With reliable R&D scale manufacturing and targeted testing platforms, Saint-Gobain has increased sub-scale stack power density by 61% and decreased interconnect cell resistance by 65% with further improvements in development.

Commentary by Dr. Valentin Fuster

Energy, Environmental, and Economic Analyses of Fuel Cell Systems

2014;():V001T03A001. doi:10.1115/FuelCell2014-6403.

One potentially attractive application of solid oxide fuel cells (SOFCs) is for combined heat and power (CHP) in light commercial buildings. An SOFC-based CHP system can be employed to efficiently serve building thermal and electric loads, thereby lowering utility bills and offering many distributed generation benefits. It is often desirable to operate SOFCs in a predominately base load manner from a hardware viewpoint. However, systems in practice will experience some load dynamics during their lifetime and furthermore, optimal economic dispatch of CHP systems frequently recommends a load-following strategy. Thus, the present work is motivated by the need to understand the dynamic response capabilities of SOFC-CHP systems. Part-load performance and dynamic load-following capabilities of a 24 kW planar SOFC system for light commercial applications was investigated through computational modeling. The SOFC and balance-of-plant component models were implemented in gPROMS modeling software. The modeling strategy of each system component and associated transients are discussed. A dynamic SOFC channel-level model, which has been verified against experimental cell data, was integrated with additional balance-of-plant (BOP) component models consisting of a fuel reformer, tail gas combustor, turbomachinery, heat exchangers, and bypass valves. The performance of the system at part-load operation displays increases in electrical efficiency and decreases in CHP efficiency, as well as a more uniform PEN temperature profile. Modeling comparisons between the responses of systems consisting of either dynamic or steady-state BOP component models are reported. A fully dynamic system-level model displays anodic fuel depletion effects and waste heat recovery transients not captured by the steady-state models. The dynamics influence the ability of an SOFC system to load follow indicating when thermal and electric storage may be necessary.

Commentary by Dr. Valentin Fuster
2014;():V001T03A002. doi:10.1115/FuelCell2014-6670.

Detailed analysis of exergy on the integrated gasification combined cycle (IGCC) incorporated with a solid oxide fuel cell (SOFC) was conducted to explore the performance characteristics of the system. The exergy destruction and exergy efficiency were analyzed at different syngas mixture compositions by varying the compressor pressure ratio. SOFC-gas turbine system included gasifier, gas cooler, SOFC, compressor and gas turbine, combustion chamber and heat recovery system generator. Results showed that using hydrogen-enriched syngas mixture increased the net power and the exergy efficiency. The highest exergy destruction occurred at the gasifier, and combustion chamber.

Commentary by Dr. Valentin Fuster
2014;():V001T03A003. doi:10.1115/FuelCell2014-6693.

The adoption of solid oxide fuel cell (SOFC) technology in power generation has been limited, in no small part, by material degradation issues affecting the stack lifetime, and hence, the economic viability. A numeric study was conducted to determine if the life of an SOFC could be extended when integrated with a recuperated gas turbine system. Dynamic modeling tools developed at the National Energy Technology Laboratory (NETL) for real-time applications were applied to evaluate life to failure for both a standalone SOFC and a hybrid SOFC gas turbine. These models were modified using empirical relations to experimental degradation data to incorporate degradation as a function of current density and fuel utilization. For the control strategy of shifting power to the turbine as fuel cell voltage degrades, the SOFC life could be extended dramatically, significantly impacting the economic potential of the technology.

Commentary by Dr. Valentin Fuster
2014;():V001T03A004. doi:10.1115/FuelCell2014-6713.

A Proton Exchange Membrane Fuel Cell Combined Heat and Power system (PEMFC-CHP) fuelled by the hydrogen-rich gas reformed from biogas may be seen as an efficient and sustainable technology. This system can provide electrical and thermal energy dynamically to residential applications. In this study, an assessment of the economic performance of an integrated biogas plant and PEMFC-CHP for Swedish electricity and heat prices is presented. The economic factors considered are the capital and operation & maintenance (O&M) costs of the biogas plant and the PEMFC-CHP, the price of heat and electricity, and the value of the digestate as fertilizer. The analysis includes two cases: 1) both biogas plant and PEMFC-CHP are located on the farm. The farm sells the electricity and heat to the power grid and district heating system, respectively; 2) the PEMFC-CHP is located in a centralized-biogas plant, not on the farm. The manure is transported from farms to the plant. The plant also sells the electricity and heat to the power grid and district heating system. The results show that the farm-based and the centralized biogas plant have almost the same biogas production cost. The electricity cost of today, expected for 2020, and for the break-even of this integrated system are 530, 305 and 197 €/MWh, respectively. With the current trend of the fuel cell industry development, this break-even price may be reached in the near future.

Commentary by Dr. Valentin Fuster

Fuels and Infrastructure for Fuel Cell and Hydrogen Energy Systems

2014;():V001T04A001. doi:10.1115/FuelCell2014-6399.

Compact and efficient fuel reforming system design is a major challenge because of strict requirements of efficient heat distribution on both the reforming and combustion side. As an alternative to traditional packed bed tubular reformers, catalytic flat plate fuel reformer offers better heat integration by combining the combustion reaction on one side and reforming reaction on the other side. In this study, with the help of a two-dimensional computational fluid dynamics (CFD) model, a catalytic flat plate fuel reformer is built and investigated its performance experimentally. The CFD model simulation results help to capture the effect of design parameters such as catalyst layer thickness, reaction rates, inlet temperature and velocity, and channel height. The CFD model study results also help to design and built the actual reformer in such a way that eliminate the limitations or uncertainties of heat and mass transfer coefficients. In our study, we experimentally evaluated the catalytic flat plate fuel reformer performance using natural gas. The effect of reformate gas on the current-voltage characteristics of a 5kW high temperature PEM fuel cell (HTPEMFC) stack is investigated extensively. The results shows that the overall system performance increases in terms of current-voltage characteristics of HTPEMFC while fed with reformate directly from the catalytic flat plate reformer.

Commentary by Dr. Valentin Fuster
2014;():V001T04A002. doi:10.1115/FuelCell2014-6431.

The Environmental Protection Agency (EPA) has estimated that 5% of air pollutants originate from small internal combustion engines (ICE) used in non-automotive applications. While there have been significant advances towards developing more sustainable systems to replace large ICEs, few designs have been implemented with the capability to replace small ICEs such as those used in the residential sector for lawn and garden equipment. Replacing these small residential internal combustion engines presents a unique opportunity for early market penetration of fuel cell technologies. This paper describes the initial efforts to build an innovative residential-scale fuel cell system using propane as its fuel source, and the deployment of this technology in a commonly used device found throughout the U.S. There are three main components to this program, including the development of the propane reforming system, fuel cell operation, and the overall system integration. This paper presents the reforming results of propane catalytic partial oxidation (cPOx). The primary parameters used to evaluate the reformer in this experiment were reformate composition, carbon concentration in the effluent, and reforming efficiency as a function of catalyst temperature and O2/C ratio. When including the lower heating value (LHV) for product hydrogen and carbon monoxide, maximum efficiencies of 84% were achieved at an O2/C ratio of 0.53 and a temperature of 940°C. Significant solid carbon formation was observed at catalyst temperatures below 750°C.

Topics: Fuel cells , oxidation
Commentary by Dr. Valentin Fuster
2014;():V001T04A003. doi:10.1115/FuelCell2014-6509.

Transient impacts on the performance of solid oxide fuel cell / gas turbine (SOFC/GT) hybrid systems were investigated using hardware-in-the-loop simulations (HiLS) at a test facility located at the U.S. Department of Energy, National Energy Technology Laboratory. The work focused on applications relevant to polygeneration systems which require significant fuel flexibility. Specifically, the dynamic response of implementing a sudden change in fuel composition from syngas to methane was examined. The maximum range of possible fuel composition allowable within the constraints of carbon deposition in the SOFC and stalling/surging of the turbine compressor system was determined.

It was demonstrated that the transient response was significantly impact the fuel cell dynamic performance, which mainly drives the entire transient in SOFC/GT hybrid systems. This resulted in severe limitations on the allowable methane concentrations that could be used in the final fuel composition when switching from syngas to methane. Several system performance parameters were analyzed to characterize the transient impact over the course of two hours from the composition change.

Commentary by Dr. Valentin Fuster
2014;():V001T04A004. doi:10.1115/FuelCell2014-6563.

Thermal management in the fuel cell component of a direct fired solid oxide fuel cell gas turbine (SOFC/GT) hybrid power system, especially during an imposed load transient, can be improved by effective management and control of the cathode air mass flow. The response of gas turbine hardware system and the fuel cell stack to the cathode air mass flow transient was evaluated using a hardware-based simulation facility designed and built by the U.S. Department of Energy, National Energy Technology Laboratory (NETL).

The disturbances of the cathode air mass flow were accomplished by diverting air around the fuel cell system through the manipulation of a hot-air bypass valve in open loop experiments. The dynamic responses of the SOFC/GT hybrid system were studied in this paper.

The evaluation included distributed temperatures, current densities, heat generation and losses along the fuel cell over the course of the transient along with localized temperature gradients. The reduction of cathode air mass flow resulted in a sharp decrease and partial recovery of the thermal effluent from the fuel cell system in the first 10 seconds. In contrast, the turbine rotational speed did not exhibit a similar trend. The collection of distributed fuel cell and turbine trends obtained will be used in the development of controls to mitigate failure and extend life during operational transients.

Commentary by Dr. Valentin Fuster
2014;():V001T04A005. doi:10.1115/FuelCell2014-6595.

Fuel cells produce exhaust waste heat that can be harnessed to either meet local heating needs or produce additional electricity via an appropriately chosen bottoming cycle. Power production can often be more economically attractive than heating due to the much higher value of electricity than heat on an equivalent energy basis, especially given fuel cell incentives and subsidies that are based on the net electrical output of the (combined cycle) fuel cell power plant. In this paper we review the application of the Organic Rankin Cycle (ORC) for power production from fuel cell waste heat, with emphasis on the resulting improvements in overall power plant power output, efficiency, economics (e.g., cents/kWh maintenance costs), and emissions levels (e.g., lb/MWh emissions). We also highlight a much less obvious advantage of ORC bottoming of fuel cells; namely, its ability to partially compensate for fuel cell stack degradation over time, and corresponding potential to extend the time required between fuel cell stack overhauls. We will also review the relative difficulty of several well established commercial applications of the ORC for power production from waste heat — such as power production from gas turbine exhaust, etc. — in comparison to fuel cell applications. We conclude that not only is the ORC ideal for fuel cell bottoming, but also that fuel cells are a nearly ideal commercial application area for the ORC. In closing, we summarize a recently completed project believed to be the world’s first commercial application of ORC technology to a fuel cell power plant. This project was completed in less than a year after its initiation, and utilizes a single ORC in conjunction with five fuel cells, all located within a fuel cell park that produces nearly 15 MW of electricity.

Commentary by Dr. Valentin Fuster
2014;():V001T04A006. doi:10.1115/FuelCell2014-6624.

Catalytic autothermal reforming (ATR) is one promising technology to effectively produce hydrogen and syngas from heavy hydrocarbon fuels for fuel cell applications. The present study describes the development of a cylindrical 1.5 kWe scale autothermal reformer for on-board SOFCs. NiO-Rh bimetallic catalysts supported on 400 cpsi cordierite monoliths were experimentally examined in the reformer. Promoters including cerium, potassium and lanthanum were introduced in the catalysts preparation to improve their performance. Dodecane (C12H26) was used as a surrogate for desulfurized commercial Jet-A fuel (C11.6H22.3) to study the hydrogen selectivity and efficiency of ATR reactions with different catalysts. Gas chromatography (GC) equipped with TCD detector was used to monitor the concentration of H2, CO, CO2 and N2 in the reformate. The catalysts screening tests were performed at the same operation conditions including inlet temperatures, reactor temperature, steam to carbon ratio and oxygen to carbon ratio. The best catalyst was reported to have efficiency about 85 percent. The optimized reactor operation temperature was reported as 700 °C.

Commentary by Dr. Valentin Fuster
2014;():V001T04A007. doi:10.1115/FuelCell2014-6649.

This article details analysis of hydrogen (H2) production based on polymer electrolyte membrane (PEM) electrolysis. This work identifies primary constraints to the success of this production pathway, primary cost drivers, and remaining Research and Development (R&D) challenges. This research assesses the potential to meet U.S. Department of Energy (DOE) H2 production and delivery (P&D) cost goals of $2 to $4/gasoline gallon equivalent (dispensed, untaxed) by 2020. Pathway analysis is performed using the DOE’s main H2A modeling tool, namely, the H2A Production model, which encapsulates the standard methods of energy, emissions, and cost analysis developed by DOE’s H2 and fuel cell technology teams. PEM electrolysis production pathways are analyzed for a distributed, forecourt H2 production system of 1,500 kilograms (kg) of H2 per day, and for a central, large, plant size H2 production system of 50,000 kg H2/day, for both current and future cases. The analysis is based in part on data from a technical and economic survey completed by four different PEM electrolyzer companies.

Model results indicate that, for PEM electrolysis, the primary cost drivers are the electricity expenditures to run the electrolyzer and the capital cost of the electrolyzer. In the future within the electrolyzer system, the balance of plant is expected to be a greater source of cost than the electrolyzer stack due to stack reductions facilitated by operation at higher current densities whereas the balance of plant remains similarly sized for the given flow. This balance between size and cost of the stack versus balance of plant could also increase difficulties in meeting efficiency improvements in the future. The H2 cost reduction is estimated to be greater moving from a Current case to a Future case, compared with moving from a Forecourt case to a Central case.

Commentary by Dr. Valentin Fuster

Materials Sets and Requirements for Fuel Cells

2014;():V001T05A001. doi:10.1115/FuelCell2014-6671.

The molten carbonate fuel cell (MCFC) is considered one of the best technologies for stationary power. This is due to its high efficiency, medium–high operating temperature, and low emissions. The MCFC operates at a temperature range from 600oC to 700oC and normally is combined with the gas turbine (GT) as a topping cycle. This work investigates the impact of Platinum/Graphene (Pt/G) on a combined cycle of MCFC-GT by applying the first and second laws of thermodynamics. The maximum work output of the hybrid cycle is ultimately calculated to be 1350 kW. The overall exergy efficiency achieved is 59.82%. Our findings reveal that there is an average 23% gain in the maximum work output, energy and exergy efficiencies when Pt/G is used as the cathode material compared to other materials such as Platinum/Carbon (Pt/C) and Platinum/Carbon cloth (Pt/CC).

Topics: Carbon , Fuel cells , Graphene
Commentary by Dr. Valentin Fuster

Modeling, Design, and Optimization for Fuel Cells

2014;():V001T06A001. doi:10.1115/FuelCell2014-6323.

The gas diffusion layers (GDLs) are key components in proton exchange membrane fuel cells and understanding fluid flow through them plays a significant role in improving fuel cell performance. We used a combination of multiple-relaxation time (MRT) lattice Boltzmann method (LBM) and X-ray micro tomography imaging technology to compare results on dependence of the permeability calculation on the different system size of the computational gas diffusion layer sample. The micro-structures of the carbon paper (HP_1.76) and carbon cloth (HP_1.733) GDL were all digitizing 3D images acquired by X-ray computed micro-tomography at a resolution of 1.76 and 1.733 microns meter respectively, and the fluid flow was simulated by applying pressure gradient in both the through-plane and in-plane direction respectively. The lattice Boltzmann method for permeability calculation has already been tested in our previous work. In this work, we will focus on the permeability calculation of the realistic gas diffusion layer samples depend on the different size samples. The results show the permeability increases with fluctuations as the porosity rises. All the permeability and porosity converge to the value of large size sample that can be regarding a representative volume element. As the porosity and permeability of these Porous samples differs significantly for each other, the anisotropic permeability is nearly same for each one. We can choose part of the sample to calculate the characters if the sample is too big to calculate. We systematically study the effect of system size and periodic boundary condition and validate Darcy’s law from the linear dependence of the flux on the body force exerted.

Commentary by Dr. Valentin Fuster
2014;():V001T06A002. doi:10.1115/FuelCell2014-6334.

Activation overpotentials, due to the reaction kinetics at the surface of the electrodes are the dominant losses in low current densities in proton exchange membrane (PEM) fuel cells. Although the Butler-Volmer equation can be employed to model the reactions at the anode and cathode, there are still ambiguities regarding the estimation and modeling of the activation losses. In this paper, the Butler-Volmer equation for both the anode and cathode is simplified. It is shown that the anode activation overpotential can be modeled using the linearized Butler-Volmer equation. The cathode activation overpotential is determined using Tafel equation. The both equations are discussed to be very accurate in the entire range of fuel cell performance. The total activation overpotential is then determined.

Commentary by Dr. Valentin Fuster
2014;():V001T06A003. doi:10.1115/FuelCell2014-6335.

In this work, a PEM fuel cell 2D-model was developed to investigate the heterogeneities existing at the surface of a cell. A study on the effects of the operating conditions on the performance and durability was carried out. An experimental validation was conducted.

Commentary by Dr. Valentin Fuster
2014;():V001T06A004. doi:10.1115/FuelCell2014-6358.

Degradation tests of two phosphoric acid (PA) doped PBI membrane based HT-PEM fuel cells were reported in this paper to investigate the effects of start/stop and the presence of methanol in the fuel to the performance degradation. Continuous tests with H2 and simulated reformate which was composed of H2, water steam and methanol as the fuel were performed on both single cells. 12-h-startup/12-h-shutdown dynamic tests were performed on the first single cell with pure dry H2 as the fuel and on the second single cell with simulated reformate as the fuel. Along with the tests electrochemical techniques such as polarization curves and electrochemical impedance spectroscopy (EIS) were employed to study the degradation mechanisms of the fuel cells. Both single cells showed an increase in the performance in the H2 continuous tests, because of a decrease in the ORR kinetic resistance probably due to the redistribution of PA between the membrane and electrodes. EIS measurement of first fuel cell during the start/stop test showed that the mass transfer resistance and ohmic resistance increased which can be attributed to the corrosion of carbon support in the catalyst layer and degradation of the PBI membrane. During the continuous test with simulated reformate as the fuel the ORR kinetic resistance and mass transfer resistance of both single cells increased. The performance of the second single cell experienced a slight decrease during the start/stop test with simulated reformate as the fuel.

Commentary by Dr. Valentin Fuster
2014;():V001T06A005. doi:10.1115/FuelCell2014-6361.

The performance of three alkaline direct ethanol fuel cells (ADEFCs) is investigated. All three use identical anode and cathode electrodes, but one uses an anion exchange membrane (AEM) and the other two use non-permselective porous separators. Ethanol was chosen as the fuel because of its low toxicity, low carbon footage and market readiness. A direct comparison between ADEFCs with and without AEM is reported. The performance of each cell is studied under different operation conditions of temperature, reactants flow rate, ethanol and KOH concentrations. The results show that with low cost porous separator, the ADEFC can reach similar power output as those using expensive AEMs. With 1 M ethanol and 1 M KOH aqueous solution, the maximum power densities of 26.04 mW/cm2 and 24.0 mW/cm2 are achieved for the ADEFC employing AEM and non-woven fabric separator, respectively. This proves the feasibility of replacing AEM with non-permselective separators. The results suggest that improving the cathode structure in order to provide a better oxygen supply is a key factor to enhance the performance of an anion exchange membrane free ADEFC.

Commentary by Dr. Valentin Fuster
2014;():V001T06A006. doi:10.1115/FuelCell2014-6378.

As fuel cells are increasingly commercialized for various applications, harmonized and industry-relevant test procedures are necessary to benchmark tests and to ensure comparability of stack performance results from different parties. This paper reports the results of parametric sensitivity tests performed based on test procedures proposed by a European project, Stack-Test. The sensitivity of a Nafion-based low temperature PEMFC stack’s performance to parametric changes was the main objective of the tests. Four crucial parameters for fuel cell operation were chosen; relative humidity, temperature, pressure, and stoichiometry at varying current density. Furthermore, procedures for polarization curve recording were also tested both in ascending and descending current directions.

Commentary by Dr. Valentin Fuster
2014;():V001T06A007. doi:10.1115/FuelCell2014-6388.

Microbial fuel cells (MFCs) are promising for simultaneous treatment of wastewater and energy production. In this study, a mathematical model for microbial fuel cells with air cathodes was developed and demonstrated by integrating biochemical reactions, Butler–Volmer expressions and mass/charge balances. The model developed is focused on describing and understanding the steady-state polarization curves of the microbial fuel cells with various levels and methods of anode-biofilm growth with air cathodes. This polarization model combines enzyme kinetics and electrochemical kinetics, and is able to describe measured polarization curves for microbial fuel cells with different anode-biofilm growth. The MFC model developed has been verified with the experimental data collected. The simulation results provide insights into the limiting physical, chemical and electrochemical phenomena and their effects on cell performance. For example, the current MFC data demonstrated performance primarily limited by cathode electrochemical kinetics.

Commentary by Dr. Valentin Fuster
2014;():V001T06A008. doi:10.1115/FuelCell2014-6407.

Mechanical reliabilities of membrane electrode assemblies (MEA) in polymer electrolyte fuel cells (PEFCs) are a major concern to fuel cell vehicles. Especially, MEAs are designed to be thinner for obtaining higher generating performance and reducing cost. Proton exchange membranes (PEM) in MEA are especially important parts. When PEFCs generate power, MEAs are in high temperature and water is generated. Hygro-thermal cyclic conditions induce the mechanical stress in MEA and cracks are formed on catalyst layers. Once cracks form on catalyst layers, cracks may propagate into PEM or on the interface between the catalyst layer and PEM. The failures of PEM induce the leak of fuel gases and result in the shortage of output power. Therefore, in order to ensure the durability of thin MEAs, it is important to know the fracture resistance of PEM.

The deformation of PEM is constrained by coated catalyst layers and crack propagates into thickness direction of PEM under the constrained condition. However, there are no available data for the fracture resistance of cracks propagating into thickness direction in MEA, because of the difficulty of measurements. Therefore, in this paper, we try to measure the fracture resistance of cracks propagating into thickness direction in PEM under several environmental conditions. Elastic-plastic fracture toughness tests for PEM were carried out in temperature and humidity controlled chamber. The results showed that the fracture resistances of crack propagation into thickness direction of PEM were strongly affected by temperature and humidity conditions.

Commentary by Dr. Valentin Fuster
2014;():V001T06A009. doi:10.1115/FuelCell2014-6445.

Direct methanol fuel cells (DMFC) are becoming a choice of a power source in the field of power electronics, and portable devices because of their high energy density. The benefits of using a fuel cell towards the environment will be enhanced if the fuel used for its application comes from renewable sources such as ethanol. A method of modeling of the performance of DMFC was developed and validated with the experimental data obtained from a passive DMFC operated under varying methanol and ethanol concentrations. Impedance spectroscopy was employed to measure ohmic, activation and mass transport losses for all concentrations. Improved performance of the cell was observed when the concentrations of the solutions were closer to stoichiometric values. The model predicted results were compared to the corresponding experimental values and found satisfactory.

Commentary by Dr. Valentin Fuster
2014;():V001T06A010. doi:10.1115/FuelCell2014-6480.

Proton exchange membrane fuel cells (PEMFCs) are useful systems because they operate at lower temperatures than other types of fuel cells. This characteristic causes water management issues. To elucidate effects of water on PEMFC performance, we developed a temperature sensor using micro-electro-mechanical systems (MEMS) techniques. This sensor was placed between the catalyst layer (CL) and the microporous layer (MPL) at the cathode. Slight effects on total cell performance were observed with the insertion of the sensor. This sensor can be applicable to typical PEMFCs without any special equipment such as a transparent separator. In-situ measurement with a temperature sensor showed that the maximum temperature rise at the cathode CL (CCL) was about 9 °C at 1.1 A/cm2. The temperature sensor also showed temperature gradients between the ribs and channels. In addition, we developed a capacitance-type humidity sensor and inserted it in the channel. In-situ measurement with a humidity sensor showed a relative humidity (RH) change in the channel. This sensor can detect not only RH but also accumulated water in the channel. Liquid water appeared in the channel at 0.7 A/cm2.

Commentary by Dr. Valentin Fuster
2014;():V001T06A011. doi:10.1115/FuelCell2014-6484.

Proton exchange membrane (PEM) fuel cells produce power with water and heat as inevitable byproducts. Accumulated liquid water within gas channel blocks the reactant flow and cause pressure drop along the gas channel. It is of extreme importance to accurately predict the liquid and gas two-phase flow pressure drop in PEM fuel cell flow channels. This pressure drop can be considered as an in-situ diagnostic tool that reveals information about the amount of liquid water accumulated within the flow channels. In this paper, the two-phase flow pressure drops are measured in ex-situ PEM fuel cell parallel flow channels. The pressure drops were measured for air mass fluxes of 2.4–6.3kg/m2s and water mass fluxes of 0.0071–1.28kg/m2s. These mass fluxes correspond to 2–5.33m/s and 7.14 × 10−6 – 0.0012m/s air and water superficial velocities, respectively. The measured two-phase flow pressure drops are then compared with different two-phase flow pressure drop models. Qualitative and quantitative comparison between the experimental results and existing models is provided in this work.

Commentary by Dr. Valentin Fuster
2014;():V001T06A012. doi:10.1115/FuelCell2014-6507.

Higher efficiency operation of PEM fuel cells needs an advanced passive way to remove product water. Water flooding in gas flow channels reduces efficiency and needs to be mitigated by a support of balance of plant design and components which results in parasitic power losses. ElectroChem’s Integrated Flow Field (IFF) design with the integration of hydrophobic and hydrophilic matrix has been proven to solve these challenges with no impact on the performance. The hydrophobic and hydrophilic matrix facilitates two phase (gas and liquid) flow to and away from the interface between the electrode membrane assembly and the flow field. A phase-separation feature of the IFF allowed the fuel cells to operate on a flow rate at its consumption rate. The IFF fuel cell has demonstrated operation at the ideal one stoichiometric ratio with 100% gas utilization and orientation independent. The IFF also served as gas humidifier through the creation of simultaneous distribution of gas and water within the cell. The self-humidification capability keeps the cell operating without the humidity of the input gas. The IFF design also enhanced the performance of water electrolysis which is a reverse process of fuel cell. The IFF supported the passive water feed to the cell and gas separation from the cell.

Commentary by Dr. Valentin Fuster
2014;():V001T06A013. doi:10.1115/FuelCell2014-6529.

This work presents the use of non-commercial software for the design and development of a multiphysics model for some aspects of a proton exchange membrane fuel cell’s (PEMFC) operation and performance. Developing the model this way gives users greater freedom to adjust and improve upon the model than with common commercial modeling software packages. By using the non-commercial partial differential equation (PDE) solver FreeFem++, which utilizes a high-level programming language based on C++, we developed a model in which the set of equations representing the mechanisms that govern PEMFC operation and the algorithms for solving it can be freely tweaked, updated or overhauled by users.

We discuss our choice of software and describe the advantages and limitations of our modeling approach, such as the flexibility provided by its open nature at the cost of added programming complexity compared to commercial packages. We also note how the geometry of the cell being modeled can easily be controlled through a set of user-defined parameters, or scripted to change for successive model runs as part of an optimization procedure or sensitivity analysis. We present results from a two-dimensional model for the cathode side in order to demonstrate the practicality of this approach.

Commentary by Dr. Valentin Fuster
2014;():V001T06A014. doi:10.1115/FuelCell2014-6565.

To achieve optimal performance of proton exchange membrane (PEM) fuel cells, effective water management is crucial. Cells need to be fabricated to operate over wide ranges of current density and cell temperature. To investigate these design and operational conditions, the present experiment utilized neutron radiography for measurement of in-situ water volumes of operating PEM fuel cells under varying operating conditions. Fuel cell performance was found to be generally inversely correlated to liquid water volume in the active area. High water concentrations restrict narrow flow field channels, limiting the reactant flow, and causing the development of performance-reducing liquid water blockages (slugs). The analysis was performed both quantitatively and qualitatively to compare the overall liquid water volume within the cell to the flow field geometry. The neutron image analysis results revealed interesting trends related to water volume as a function of time. At temperatures greater than 25°C, the total liquid water volume at start-up in the active area was the lowest at 1.5 A/cm2. At 25°C, 0.1 A/cm2 performed with the least amount of liquid water accumulation. However, as the reaction progressed at temperatures above 25°C, there was a crossover point where 0.1 A/cm2 accumulated less water than 1.5 A/cm2. The higher the temperature, the longer the time required to reach this crossover point. Results from the current density analysis showed a minimization of water slugs at 1.5 A/cm2, while the temperature analysis showed unexpectedly that, independent of current density, the condition with lowest water volume was always 35°C.

Commentary by Dr. Valentin Fuster
2014;():V001T06A015. doi:10.1115/FuelCell2014-6572.

Several experiments have proved that water in liquid phase can be present at the anode of a PEM fuel cell due to vapor condensation resulting in mass transport losses. Nevertheless, it is not yet well understood where exactly water tends to cumulate and how the design of the gas channel (GC) and gas diffusion layer (GDL) could be improved to limit water cumulation. In the present work a three-dimensional lattice Boltzmann based model is implemented in order to simulate the water cumulation at the GC-GDL interface at the anode of a PEM fuel cell. The numerical model incorporates the H2-H2O mixture equation of state and spontaneously simulates phase separation phenomena. Different simulations are carried out varying pressure gradient, pore size and relative height of the GDL. Results reveal that, once saturation conditions are reached, water tends to cumulate in two main regions: the upper and side walls of the GC and the GC-GDL interface, resulting in a limitation of the reactant diffusion from the GC to the GDL. Interestingly, the cumulation of liquid water at the interface is found to diminish as the relative height of the GDL increases.

Commentary by Dr. Valentin Fuster
2014;():V001T06A016. doi:10.1115/FuelCell2014-6574.

Temperature and relative humidity cycles play an important role in the initiation and propagation of mechanical damage in the PEM fuel cell membrane electrode assembly (MEA). However, there have been few studies on the mechanical damage evolution in PEM fuel cells due to humidity and temperature variations. In this study, we investigate the damage propagation in the MEA, with a special focus on the membrane/CL interface. A finite element model based on cohesive zone theory is developed to describe the effect of relative humidity (RH) amplitude on mechanical damage propagation in the MEA. Results showed that having larger RH variation in the applied cycles can result in up to 3.4 times higher fatigue stresses at the interface, and hence a considerably faster rate for delamination propagation.

Commentary by Dr. Valentin Fuster
2014;():V001T06A017. doi:10.1115/FuelCell2014-6635.

Proton Exchange Membrane (PEM) fuel cells require effective water transport away from the cathode to ensure stable operation. Many existing water management strategies involve active methods, reducing system efficiency by introducing parasitic losses. In the present work, we report on the improved design and fabrication of a passive water management scheme involving UV-catalyzed porous polymer wicks. The design features two connected porous domains consisting of a methacrylate-based transport layer and polyvinyl alcohol storage layer.

In our previous prototype, large water transport lengths (∼12 mm) prevented adequate removal of generated water. The capillary pressure drop across the two porous domains was insufficient to drive a flow rate matched to the rate of generation. Thus, the current design produces a shorter transport distance (∼3 mm) by developing a new vertical design. An independently produced SU-8 photolithographic mold is incorporated to improve the fabrication process.

Commentary by Dr. Valentin Fuster
2014;():V001T06A018. doi:10.1115/FuelCell2014-6650.

This paper presents results from an investigation concerning load-induced degradation, recovery, and control of solid oxide fuel cells (SOFCs). In this study, commercially available SOFCs were subject to extended over-current conditions, followed by periods of open-circuit operation. During times of current loading, degradation was observed in the cells’ electrical performance through polarization and electrochemical impedance spectroscopy (EIS) measurements. These measurements showed an increase in the polarization curve’s ohmic region slope, i.e. large-signal resistance, as well as an increase in the cell’s small-signal low-frequency impedance. The degradation was temporary however, as the electrical performance recovered during times of open-circuit operation. These results, attributed to electrochemically-induced oxidation and reduction of nickel in the anode, suggest the degradation phenomenon is controllable via the electrical terminals. As such, an additional test was performed on an SOFC powering a pulse-width modulated load, with the load’s duty-cycle negatively proportional to the cell’s large-signal resistance. Polarization and EIS measurements taken during this test showed that despite the controlled load, degradation occurred throughout the test. However, post-test scanning electron microscope images revealed cracks in the cell’s cathode along the boundary between the active and bulk layers. This type of cracking was not observed in the original degradation and recovery tests, suggesting that the degradation observed in the controlled load test was irreversible and caused by a separate phenomenon.

Commentary by Dr. Valentin Fuster

Production and Scale-Up of Electrochemical Systems

2014;():V001T07A001. doi:10.1115/FuelCell2014-6398.

With the ever-increasing addition of wind and solar renewable energy to the traditional electric grid, the need for energy storage also grows. A recent study projects the value of energy storage for wind and solar integration worldwide to exceed $30 Billion by 2023 [1]. Hydrogen from electrolysis is a promising technology for renewable energy capture as it has the capability to store massive amounts of energy in a relatively small volume. In addition, electrolysis can also provide ancillary services to the grid such as frequency regulation and load shifting resulting in multiple value streams. The hydrogen produced can alternatively be injected into the natural gas pipeline (thus making that energy carrier more green), in the production of high value chemicals such as ammonia, in upgrading of methanization-produced biogas, or used as a transportation fuel.

Europe in particular has been committed to these pathways and making heavy investment in both materials research and system design and development as well as technology demonstration. In Germany, hydrogen is looked upon as a key part of the energy storage solution under “Energiewende,” their national sustainable energy transition plan. Hydrogen provides a unique link between the electric and gas grid infrastructures (often referred to as “Power-to-Gas”). Germany is also considered the global leader in biogas energy generation, with 18,244 GWh of generation in 2012 forecasted to grow to 28,265 GWh by 2025 [2].

Water electrolysis has benefits over other hydrogen generation technologies due to the lack of carbon footprint when integrated with a renewable source of energy. Specifically, proton exchange membrane (PEM) electrolysis is a promising technology for hydrogen generation applications because of the lack of corrosive electrolytes, small footprint, and ability to generate at high pressure, requiring only water and an energy source. Several companies have already announced plans to develop megawatt (MW) commercial scale PEM electrolysis units in the 2014–2015 timeframe for these applications. There have also been recent announcements of large scale renewable energy storage project based on electrolysis.

Commentary by Dr. Valentin Fuster
2014;():V001T07A002. doi:10.1115/FuelCell2014-6643.

A design for manufacture and assembly (DFMA™) analysis is applied to future bus and automotive fuel cell vehicle (FCV) system designs. This DFMA™ analysis is used to identify (1) optimal fuel cell system (FCS) operating parameters for system cost minimization, (2) FCV designs appropriate for volume manufacture, (3) FCV manufacturing supply chain designs, (4) projected future capital costs of FCVs at varying manufacturing rates, and (5) primary cost drivers. This DFMA™ analysis focuses on the FCS drive train. It excludes fuel storage, the electric drive drain, and all other parts of the vehicle (chassis, exterior, etc.). These FCSs are envisioned to use low temperature proton exchange membrane (LT PEM) stacks to convert hydrogen fuel into electric power. Models are developed to minimize LT PEM fuel cell system costs by finding the cost optimal combination of (1) stack operating pressure, (2) cell voltage, (3) platinum (Pt) catalyst loading, (4) stoichiometric ratio of oxygen, and (5) coolant stack exit temperature. A multi-variable Monte Carlo sensitivity analysis indicates, with 90% confidence, that a FCS producing peak net 160 kilowatt-electric (kWe) for a bus application and produced at a rate of 1,000 FCS/year (yr) is expected to cost between $251/kWe and $334/kWe. Similarly, a peak net 80 kWe automotive FCS manufactured at a rate of 500,000 FCSs/year is estimated to cost between $51/kWe and $65/kWe, with 90% confidence. Total FCS costs are the sum of PEM stack and balance of plant (BOP) costs. The BOP components represent 32% of the bus FCS costs and 48% of the automotive system cost.

Commentary by Dr. Valentin Fuster


2014;():V001T08A001. doi:10.1115/FuelCell2014-6368.

Hydrogen is a resource that provides energy and forms water only after reacting with oxygen. Because there are no emissions such as greenhouse gases when hydrogen is converted to produce energy, it is considered one of the most important energy resources for addressing the problems of global warming and air pollution. Additionally, hydrogen can be useful for constructing “smart grid” infrastructure because electrical energy from other renewable energy sources can be stored in the form of chemical energy by electrolyzing water, creating hydrogen.

Among the many hydrogen generation systems, solid oxide electrolysis cells (SOECs) have attracted considerable attention as advanced water electrolysis systems because of their high energy conversion efficiency and low use of electrical energy. To find the relationship between operating conditions and the performance of SOECs, research has been conducted both experimentally, using actual SOEC cells, and numerically, using computational fluid dynamics (CFD). In this investigation, we developed a 3-D simulation model to analyze the relationship between the operating conditions and the overall behavior of SOECs due to different contributions to the over-potential.

All SOECs involve the transfer of mass, momentum, species, and energy, and these properties are correlated. Furthermore, all of these properties have a direct influence on the concentration of the gases in the electrodes, the pressure, the temperature and the current density. Therefore, the conservation equations for mass, momentum, species, and energy should be included in the simulation model to calculate all terms in the transfer of mass, heat and fluid. In this simulation model, the transient term was neglected because the steady state was assumed.

All governing equations were calculated using Star-CD (CD Adapco, U.S). The source terms in the governing equations were calculated with in-house code, i.e., user defined functions (UDF), written in FORTRAN 77, and these were linked to the Star-CD solver to calculate the transfer processes. Simulations were performed with various cathode inlet gas compositions, anode inlet gas compositions, cathode thickness, and electrode porosity to identify the main parameters related to performance.

Commentary by Dr. Valentin Fuster

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