An inverse geometry design problem for optimization of single serpentine flow field of PEM fuel cell

The cathode flow-field design of a proton exchange membrane fuel cell (PEMFC) determines its reactant transport rates to the catalyst layer and removal rates of liquid water from the cell. This study optimizes the cathode flow field for a single serpentine PEM fuel cell with 5 channels using the heights of channels 2–5 as search parameters. This work describes an optimization approach that integrates the simplified conjugated-gradient scheme and a three-dimensional, two-phase, non-isothermal fuel cell model. The proposed optimal serpentine design, which is composed of three tapered channels (channels 2–4) and a final diverging channel (channel 5), increases cell output power by 11.9% over that of a cell with straight channels. These tapered channels enhance main channel flow and sub-rib convection, both increasing the local oxygen transport rate and, hence, local electrical current density. A diverging, final channel is preferred, conversely, to minimize reactant leakage to the outlet. The proposed combined approach is effective in optimizing the cathode flow-field design for a single serpentine PEMFC. The role of sub-rib convection on cell performance is demonstrated.     

Numerical and experimental study of three-dimensional fluid flow in the bipolar plate of a PEM electrolysis cell

The bipolar plate is one of the key components in proton exchange membrane (PEM) electrolysis cell stacks for hydrogen production. Bipolar plates of electrolysis cells must be properly designed to distribute reactant (water) evenly, and efficient PEM electrolysis cell stacks will require optimized bipolar plates. Numerical simulations and experimental measurements of three-dimensional water flow were performed for the purpose of examining pressure and velocity distributions in the bipolar plate of a PEM electrolysis cell. For the studied flow range, the computed pressure drops agree very favorably with the measurements. Results show that pressure decreases from the inlet tube to the exit tube along the diagonal direction. Both velocity and temperature distributions are very non-uniform in the channels. A minimum of the peak values of mainstream velocity component in the channels develops in the center of the test plate. The maximum of these peak values appears in the channel near the exit tube. For the studied flow levels, these lines along which the mainstream velocity component is a peak in the channel almost overlay with each other, except that minor difference can be noticed in the channel near the exit tube.     

Effect of humidity of reactants on the cell performance of PEM fuel cells with parallel and interdigitated flow field designs

This study investigates the effects of the relative humidity (RH) of the reactants on the cell performance and local transport phenomena in proton exchange membrane fuel cells with parallel and interdigitated flow fields. A three-dimensional model was developed taking into account the effect of the liquid water formation on the reactant transport. The results indicate that the reactant RH and the flow field design all significantly affect cell performance. For the same operating conditions and reactant RH, the interdigitated design has better cell performance than the parallel design. With a constant anode RH = 100%, for lower operating voltages, a lower cathode RH reduces cathode flooding and improves cell performance, while for higher operating voltages, a higher cathode RH maintains the membrane hydration to give better cell performance. With a constant cathode RH = 100%, for lower operating voltages, a lower anode RH not only provides more hydrogen to the catalyst layer to participate in the electrochemical reaction, but also increases the difference in the water concentrations between the anode and cathode, which enhances back-diffusion of water from the cathode to the anode, thus reducing cathode flooding to give better performance. However, for higher operating voltages, the cell performance is not dependent on the anode RH.     

Effects of modified flow field on optimal parameters estimation and cell performance of a PEM fuel cell with the Taguchi method

The study applies a three-dimensional model simulating the transport phenomenon and electrochemical reactions of full scale serpentine channels to determine the best arrangement of cuboid rows at the axis in the anode and cathode channels. With the best arrangement of the cuboid rows in the channels, the Taguchi methodology is used in the experiment to obtain the optimal operating parameters for three objectives with the minimum pressure drops in anode and cathode channels, and maximum electrical power. The results show that the interactions of flow fields between each cuboid and the current collector surface generate less overall deflection effect and force more reactant gases into the catalyst layer to have more uniform current density distributions. The electrical power is 30% greater for the three objectives optimization than for minimum pressure drops optimization and the pressure drops 275% less for the three objectives optimization than for maximum electrical power optimization.     

Effects of serpentine flow field with outlet channel contraction on cell performance of proton exchange membrane fuel cells

A serpentine flow field with outlet channels having modified heights or lengths was designed to improve reactant utilization and liquid water removal in proton exchange membrane (PEM) fuel cells. A three-dimensional full-cell model was developed to analyze the effects of the contraction ratios of height and length on the cell performance. Liquid water formation, that influences the transport phenomena and cell performance, was included in the model. The predictions show that the reductions of the outlet channel flow areas increase the reactant velocities in these regions, which enhance reactant transport, reactant utilization and liquid water removal; therefore, the cell performance is improved compared with the conventional serpentine flow field. The predictions also show that the cell performance is improved by increments in the length of the reduced flow area, besides greater decrements in the outlet flow area. If the power losses due to pressure drops are not considered, the cell performance with the contracted outlet channel flow areas continues to improve as the outlet flow areas are reduced and the lengths of the reduced flow areas are increased. When the pressure losses are also taken into account, the optimal performance is obtained at a height contraction ratio of 0.4 and a length contraction ratio of 0.4 in the present design.     

Secondary flow on the performance of PEMFC with blocks in the serpentine flow field

A three-dimensional, two-phase, steady-state numerical model of PEMFC with serpentine flow field was set up. The rectangular or triangular blocks were arranged in the cathode channel to improve cell performance. The results showed that the arranged blocks in the channel can effectively enhance the mass transfer of the reactant, thus improve cell performance. The triangular block has better cell performance in comparison with the rectangular block. The block arranged in the rear of the turn has the best cell performance. The reason for the better cell performance of the arranged block is the combination of the under-rib flow and the secondary flow generated by the block. The secondary flow generated by the block is the main reason for the region near the block. Meanwhile, the under-rib flow is the main reason for the region far away from the block.     

Electrochemical performances of PEM water electrolysis cells and perspectives

Proton Exchange Membrane (PEM) water electrolysis is potentially interesting for the decentralized production of hydrogen from renewable energy sources. The European Commission (EC) is actively supporting different projects within the 6th and 7th Framework Programmes. The purpose of this paper is to provide a summary of most significant scientific and technological achievements obtained at the end of the GenHyPEM project (FP6, 2005-2008), and to discuss future perspectives. Using carbon-supported platinum at the cathode for the hydrogen evolution reaction (HER) and iridium at the anode for the oxygen evolution reaction (OER), efficient membrane - electrode assemblies have been prepared and characterized using cyclic voltametry and electrochemical impedance spectroscopy. Charge densities and impedances of lab-scale PEM cells have been measured and used as references to optimize the performances of a GenHy^®1000 PEM water electrolyser (1 Nm³ H₂/h) and then to extend the production capacity up to 5 Nm³ H₂/h. Different non-noble electrocatalysts have been successfully tested to replace platinum at the cathode. Some current limitations and future perspectives of the technology are outlined and discussed.     

Local transport phenomena and cell performance of PEM fuel cells with various serpentine flow field designs

The flow field design in bipolar plates is very important for improving reactant utilization and liquid water removal in proton exchange membrane fuel cells (PEMFCs). A three-dimensional model was used to analyze the effect of the design parameters in the bipolar plates, including the number of flow channel bends, number of serpentine flow channels and the flow channel width ratio, on the cell performance of miniature PEMFCs with the serpentine flow field. The effect of the liquid water formation on the porosities of the porous layers was also taken into account in the model while the complex two-phase flow was neglected. The predictions show that (1) for the single serpentine flow field, the cell performance improves as the number of flow channel bends increases; (2) the single serpentine flow field has better performance than the double and triple serpentine flow fields; (3) the cell performance only improves slowly as the flow channel width increases. The effects of these design parameters on the cell performance were evaluated based on the local oxygen mass flow rates and liquid water distributions in the cells. Analysis of the pressure drops showed that for these miniature PEMFCs, the energy losses due to the pressure drops can be neglected because they are far less than the cell output power.     

A comprehensive review on PEM water electrolysis

Hydrogen is often considered the best means by which to store energy coming from renewable and intermittent power sources. With the growing capacity of localized renewable energy sources surpassing the gigawatt range, a storage system of equal magnitude is required. PEM electrolysis provides a sustainable solution for the production of hydrogen, and is well suited to couple with energy sources such as wind and solar. However, due to low demand in electrolytic hydrogen in the last century, little research has been done on PEM electrolysis with many challenges still unexplored. The ever increasing desire for green energy has rekindled the interest on PEM electrolysis, thus the compilation and recovery of past research and developments is important and necessary. In this review, PEM water electrolysis is comprehensively highlighted and discussed. The challenges new and old related to electrocatalysts, solid electrolyte, current collectors, separator plates and modeling efforts will also be addressed. The main message is to clearly set the state-of-the-art for the PEM electrolysis technology, be insightful of the research that is already done and the challenges that still exist. This information will provide several future research directions and a road map in order to aid scientists in establishing PEM electrolysis as a commercially viable hydrogen production solution.     

Numerical modeling of three-dimensional two-phase gas–liquid flow in the flow field plate of a PEM electrolysis cell

Numerical simulations were performed for three-dimensional two-phase water/oxygen flow in the flow field plate at the anode side of a PEM electrolysis cell. The mixture model was used to simulate two phases for the purpose of examining flow features in the flow field plate in order to effectively guide the design of electrolysis cells. The water flow rate was maintained as a constant of 260 mL/min, while the flow rate of oxygen generation was assumed to change from 0 to 14 mg/s. The obtained results including the velocity, pressure, and volume fraction distributions are presented and discussed. It is found that the obtained results for single-phase flow cases cannot be linearly extrapolated into the two-phase flow cases. The irregular velocity profile (locally low velocity magnitude near the exit port section) is not observed when the flow rate of oxygen generation is relatively low. As the mass flow rate of oxygen generation increases, reverse flow develops inside the flow channels.     

Modeling two-phase flow in PEM fuel cell channels

This paper is concerned with the simultaneous flow of liquid water and gaseous reactants in mini-channels of a proton exchange membrane (PEM) fuel cell. Envisaging the mini-channels as structured and ordered porous media, we develop a continuum model of two-phase channel flow based on two-phase Darcy's law and the M² formalism, which allow estimate of the parameters key to fuel cell operation such as overall pressure drop and liquid saturation profiles along the axial flow direction. Analytical solutions of liquid water saturation and species concentrations along the channel are derived to explore the dependences of these physical variables vital to cell performance on operating parameters such as flow stoichiometric ratio and relative humility. The two-phase channel model is further implemented for three-dimensional numerical simulations of two-phase, multi-component transport in a single fuel-cell channel. Three issues critical to optimizing channel design and mitigating channel flooding in PEM fuel cells are fully discussed: liquid water buildup towards the fuel cell outlet, saturation spike in the vicinity of flow cross-sectional heterogeneity, and two-phase pressure drop. Both the two-phase model and analytical solutions presented in this paper may be applicable to more general two-phase flow phenomena through mini- and micro-channels.     

Efficient hydrogen production from aqueous methanol in a PEM electrolyzer with porous metal flow field: Influence of PTFE treatment of the anode gas diffusion layer

In a proton exchange membrane (PEM) methanol electrolyzer, the even supply of reactant to and the smooth removal of carbon dioxide from the anode are very important in order to achieve a high hydrogen production performance. An appropriate design of flow field and gas diffusion layer (GDL) is a key factor in satisfying the above requirements. Previous research has shown that hydrogen production performance of the PEM methanol electrolyzer cell was largely improved with a porous flow field made of sintered spherical metal powder compared with a conventional groove type flow field. Based on this improvement, the current study investigated the influence of polytetrafluoroethylene (PTFE) treatment of the anode GDL on hydrogen production performance of the PEM methanol electrolyzer with porous metal flow fields. Influences of operating conditions such as methanol concentration and cell temperature with the flow field were also investigated.     

Novel serpentine-baffle flow field design for proton exchange membrane fuel cells

An appropriate flow field in the bipolar plates of a fuel cell can effectively enhance the reactant transport rates and liquid water removal efficiency, improving cell performance. This paper proposes a novel serpentine-baffle flow field (SBFF) design to improve the cell performance compared to that for a conventional serpentine flow field (SFF). A three-dimensional model is used to analyze the reactant and product transport and the electrochemical reactions in the cell. The results show that at high operating voltages, the conventional design and the baffled design have the same performance, because the electrochemical rate is low and only a small amount of oxygen is consumed, so the oxygen transport rates for both designs are sufficient to maintain the reaction rates. However, at low operating voltages, the baffled design shows better performance than the conventional design. Analyses of the local transport phenomena in the cell indicate that the baffled design induces larger pressure differences between adjacent flow channels over the entire electrode surface than does the conventional design, enhancing under-rib convection through the electrode porous layer. The under-rib convection increases the mass transport rates of the reactants and products to and from the catalyst layer and reduces the amount of liquid water trapped in the porous electrode. The baffled design increases the limiting current density and improves the cell performance relative to conventional design.     

Numerical study of cell performance and local transport phenomena in PEM fuel cells with various flow channel area ratios

Three-dimensional models of proton exchange membrane fuel cells (PEMFCs) with parallel and interdigitated flow channel designs were developed including the effects of liquid water formation on the reactant gas transport. The models were used to investigate the effects of the flow channel area ratio and the cathode flow rate on the cell performance and local transport characteristics. The results reveal that at high operating voltages, the cell performance is independent of the flow channel designs and operating parameters, while at low operating voltages, both significantly affect cell performance. For the parallel flow channel design, as the flow channel area ratio increases the cell performance improves because fuel is transported into the diffusion layer and the catalyst layer mainly by diffusion. A larger flow channel area ratio increases the contact area between the fuel and the diffusion layer, which allows more fuel to directly diffuse into the porous layers to participate in the electrochemical reaction which enhances the reaction rates. For the interdigitated flow channel design, the baffle forces more fuel to enter the cell and participate in the electrochemical reaction, so the flow channel area ratio has less effect. Forced convection not only increases the fuel transport rates but also enhances the liquid water removal, thus interdigitated flow channel design has higher performance than the parallel flow channel design. The optimal performance for the interdigitated flow channel design occurs for a flow channel area ratio of 0.4. The cell performance also improves as the cathode flow rate increases. The effects of the flow channel area ratio and the cathode flow rate on cell performance are analyzed based on the local current densities, oxygen flow rates and liquid water concentrations inside the cell.     

Numerical and experimental investigation of cascade type serpentine flow field of reactant gases for improving performance of PEM fuel cell

The distribution of reactant gases in polymer electrolyte membrane fuel cells (PEMFCs) plays a pivotal role in current density distribution, temperature distribution, and water concentration. Problems such as flooding or drying of the membrane are caused by the non-uniformity of the above mentioned parameters resulting in a reduced membrane electrode assembly (MEA) life time. In this study, a new cascade type serpentine flow field is introduced and the concept of design is explained. The simulation results are in good agreement with the literature. The optimal channel to rib ratio is obtained using simulation results. The results show that the proposed flow field produces a uniform current density and local stoichiometry as well as an improved water management. It is also determined that the two phase numerical method can estimate experimental results correctly.     

Is iridium demand a potential bottleneck in the realization of large-scale PEM water electrolysis?

Proton exchange membrane water electrolysis (PEMWE) is a key technology for future sustainable energy systems. Proton exchange membrane (PEM) electrolysis cells use iridium, one of the scarcest elements on earth, as catalyst for the oxygen evolution reaction. In the present study, the expected iridium demand and potential bottlenecks in the realization of PEMWE for hydrogen production in the targeted GW a^?1 scale are assessed in a model built on three pillars: (i) an in-depth analysis of iridium reserves and mine production, (ii) technical prospects for the optimization of PEM water electrolyzers, and (iii) PEMWE installation rates for a market ramp-up and maturation model covering 50 years. As a main result, two necessary preconditions have been identified to meet the immense future iridium demand: first, the dramatic reduction of iridium catalyst loading in PEM electrolysis cells and second, the development of a recycling infrastructure for iridium catalysts with technical end-of-life recycling rates of at least 90%.     

Experimental investigation on water and heat management in a PEM fuel cell using response surface methodology

Water and heat management are the most critical issues for the performance of proton exchange membrane (PEM) fuel cells. They can be provided by keeping hydrogen flow rate, oxygen flow rate, cell temperature and humidification temperature under control. In this study, the effects of these parameters on the power density of proton exchange membrane (PEM) fuel cell which has 25 cm² active area have been examined experimentally using hydrogen on the anode side and oxygen on the cathode side. Response Surface Methodology (RSM) has been applied to optimize these operation parameters of proton exchange membrane (PEM) fuel cell. The test responses are the maximum output power density. ANOVA (analysis of variance) analyses are used to compute the effects and the contributions of the various factors to the fuel cell maximal power density. The use of this design shows also how it is possible to reduce the number of experiments. Hydrogen flow rate, oxygen flow rate, humidification temperature and cell temperature were the main parameters to have been varied between 2.5–5 L/min, 3–5 L/min, 40–70 °C and 40–80 °C in the analyses. The maximum power density was found as 241.977 mW/cm².     

PEM steam electrolysis at 130 °C using a phosphoric acid doped short side chain PFSA membrane

Steam electrolysis test with a phosphoric acid doped Aquivion™ membrane was successfully conducted and current densities up to 775 mA cm⁻² at 1.8 V was reached at 130 °C and ambient pressure. A new composite membrane system using a perfluorosulfonic acid membrane (Aquivion™) as matrix and phosphoric acid as proton conducting electrolyte was developed. Traditional perfluorosulfonic acid membranes do not possess sufficient dimensional stability and proton conductivity to be used at elevated temperatures and ambient pressures. The elevated temperature, high potentials and acidic conditions implied that a new and highly corrosion resistant construction material was needed. Tantalum coated stainless steel felt was tested and found suitable as the anode gas diffusion layer.     

Optimization of blocked flow field performance of proton exchange membrane fuel cell with auxiliary channels

The flow field optimization design is one of the important methods to improve the performance of proton exchange membrane fuel cell (PEMFC). In this study, a new structure with staggered blocks on the parallel flow channels of PEMFC and auxiliary flow channels under the ribs is proposed. Through numerical calculation method, the effect of blocks auxiliary flow field (BAFF) on pressure drop, reactant distribution and liquid water removal in the fuel cells are investigated. The results show that when the operating voltage is 0.5 V, the current density of BAFF is 21.74% higher than that of the straight parallel flow field (SPFF), and the power density reaches 0.65 W cm^?2. BAFF improves performance by equalizing the pressure drop across sub-channels, promoting the uniform distribution of reactant, and enhancing transport across the ribs. In addition, through parameter analysis, it is found that BAFF can discharge liquid water in time at the conditions of high humidification, high current density and low temperature, which ensures the output performance of the fuel cell and improves the durability of the fuel cell. This paper provides new ideas for the improvement of PEMFC flow field design, which is beneficial to the development of PEMFC with high current density.