• Energy Research

AbstractA two‐dimensional, non‐isothermal, two‐phase model of a polymer electrolyte fuel cell (PEFC) is presented. The model is developed for conditions where variations in the streamwise direction are negligible. In addition, experiments were conducted with a segmented cell comprised of net flow fields. The, experimentally obtained, current distributions were used to validate the PEFC model developed. The PEFC model includes species transport and the phase change of water, coupled with conservation of momentum and mass, in the porous backing of the cathode, and conservation of charge and heat throughout the fuel cell. The current density in the active layer at the cathode is modelled with an agglomerate model, and the contact resistance for heat transfer over the material boundaries is taken into account. Good agreement was obtained between the modelled and experimental polarization curves. A temperature difference of 6 °C between the bipolar plate and active layer on the cathode, and a liquid saturation of 6% at the active layer in the cathode were observed at 1 A cm–2.

AbstractA two‐dimensional, non‐isothermal, two‐phase model of a polymer electrolyte fuel cell (PEFC) is presented. The model is developed for conditions where variations in the streamwise direction are negligible. In addition, experiments were conducted with a segmented cell comprised of net flow fields. The, experimentally obtained, current distributions were used to validate the PEFC model developed. The PEFC model includes species transport and the phase change of water, coupled with conservation of momentum and mass, in the porous backing of the cathode, and conservation of charge and heat throughout the fuel cell. The current density in the active layer at the cathode is modelled with an agglomerate model, and the contact resistance for heat transfer over the material boundaries is taken into account. Good agreement was obtained between the modelled and experimental polarization curves. A temperature difference of 6 °C between the bipolar plate and active layer on the cathode, and a liquid saturation of 6% at the active layer in the cathode were observed at 1 A cm–2.

In polymer electrolyte fuel cells (PEFCs) gas diffusion backings (GDBs) have a significant effect on water management and cell performance. In this study, methods for characterizing GDB performance by fuel cell testing and ex situ measurements are presented. The performance of four different commercial GDB materials was tested and significant differences were found between the materials. While the performance and behavior are almost similar in the single-phase region, the flooding behavior of different GDBs in the two-phase region varies widely. The results show that using high clamping pressures increases cell flooding, but the increase varies from material to material. Increased flooding is caused by the combination of decreased porosity and a temperature difference between GDB and current collector. Furthermore, it was observed that the decrease in porosity due to cell compression and corresponding increase in mass-transfer resistance should be studied in the single-phase region, because flooding of the GDB easily becomes the dominating source of mass-transfer resistance. In addition, a literature review on GDB studies and characterization methods was carried out. The review revealed a lack of an established GDB testing regime and the absence of a relation between physical properties of the GDB and fuel cell performance.

In polymer electrolyte fuel cells (PEFCs) gas diffusion backings (GDBs) have a significant effect on water management and cell performance. In this study, methods for characterizing GDB performance by fuel cell testing and ex situ measurements are presented. The performance of four different commercial GDB materials was tested and significant differences were found between the materials. While the performance and behavior are almost similar in the single-phase region, the flooding behavior of different GDBs in the two-phase region varies widely. The results show that using high clamping pressures increases cell flooding, but the increase varies from material to material. Increased flooding is caused by the combination of decreased porosity and a temperature difference between GDB and current collector. Furthermore, it was observed that the decrease in porosity due to cell compression and corresponding increase in mass-transfer resistance should be studied in the single-phase region, because flooding of the GDB easily becomes the dominating source of mass-transfer resistance. In addition, a literature review on GDB studies and characterization methods was carried out. The review revealed a lack of an established GDB testing regime and the absence of a relation between physical properties of the GDB and fuel cell performance.

A 50 kW PEMFC pilot plant has been operated 4400 h using hydrogen originating from a sodium chlorate production process after standard industry purification processes were applied. The first stage of the fuel cell system operation was performed using anode gas recirculation, while in the other stages an open anode configuration was applied. The fuel cell system did not show extensive degradation despite the low quality of the hydrogen and frequent shut-downs. The average degradation rate was 2–3 μV per hour at low and medium currents (10–150 A). The main causes for any unreliability were found to be hydrogen supply side system components, namely pressure reducers and valves. Recommendations are given for the improvement of both PEMFC power plant design and operation for industrial hydrogen applications.

A 50 kW PEMFC pilot plant has been operated 4400 h using hydrogen originating from a sodium chlorate production process after standard industry purification processes were applied. The first stage of the fuel cell system operation was performed using anode gas recirculation, while in the other stages an open anode configuration was applied. The fuel cell system did not show extensive degradation despite the low quality of the hydrogen and frequent shut-downs. The average degradation rate was 2–3 μV per hour at low and medium currents (10–150 A). The main causes for any unreliability were found to be hydrogen supply side system components, namely pressure reducers and valves. Recommendations are given for the improvement of both PEMFC power plant design and operation for industrial hydrogen applications.

Ejectors are durable and inexpensive equipment for realizing hydrogen recirculation in proton exchange membrane fuel cell (PEMFC) systems. In the present work, a hydrogen recirculation ejector targeted for high turndown ratio operation in a 5 kWe PEMFC system was designed, manufactured with 3D-printing, and characterized experimentally with both air and humid hydrogen. The ejector was modeled at the experimental conditions with computational fluid dynamics (CFD) assuming 2D axisymmetric flow and with three turbulence models. A systematic comparison of experimental and simulation results was conducted with humid hydrogen at conditions covering the entire operating map up to 6 bar gauge primary pressure. The simulation results deviate on average 60%-70% from the experimental results, the deviation being less pronounced at conditions relevant in PEMFC applications. The SST k-? turbulence model was identified to agree best overall with the experimental data while the RNG and Realizable k-e turbulence models were observed to accurately predict the position of maximum ejector efficiency. Hence, the SST k-? model is more useful for predicting ejector performance while one of the two k-e models should be adopted when optimizing ejector design.

Ejectors are durable and inexpensive equipment for realizing hydrogen recirculation in proton exchange membrane fuel cell (PEMFC) systems. In the present work, a hydrogen recirculation ejector targeted for high turndown ratio operation in a 5 kWe PEMFC system was designed, manufactured with 3D-printing, and characterized experimentally with both air and humid hydrogen. The ejector was modeled at the experimental conditions with computational fluid dynamics (CFD) assuming 2D axisymmetric flow and with three turbulence models. A systematic comparison of experimental and simulation results was conducted with humid hydrogen at conditions covering the entire operating map up to 6 bar gauge primary pressure. The simulation results deviate on average 60%-70% from the experimental results, the deviation being less pronounced at conditions relevant in PEMFC applications. The SST k-? turbulence model was identified to agree best overall with the experimental data while the RNG and Realizable k-e turbulence models were observed to accurately predict the position of maximum ejector efficiency. Hence, the SST k-? model is more useful for predicting ejector performance while one of the two k-e models should be adopted when optimizing ejector design.