• Energy Research

Abstract In the present work, a two-dimensional, transient, isothermal, two-phase, multicomponent transport model was considered for the anode-side electrode of a PEMFC. The governing equations of two-phase flow in the PEM fuel cell were discretized by finite volume method, and the SIMPLE algorithm was used to handle the pressure-velocity coupling. The discretized governing equations of the model were numerically solved on a non-uniform grid with an in-house developed code. The simulation was performed for velocity, pressure, concentration of species, and liquid water saturation in the anode side of the PEMFC. At first, the steady-state and transient effects of introducing the CO-contaminated hydrogen on the cell performance were investigated. Then, a comprehensive investigation of the commonly used mitigation techniques including the effect of air or oxygen bleeding, elevation of temperature and the effect of using CO-tolerant catalysts (PtRu/C), was conducted. The numerical results of the model were compared and validated with the experimental data. The results indicated that even using a low CO concentration, leads to significant degradation of the fuel cell output current density (about 30% of the output current was lost within 30 min when the hydrogen is pre-mixed with 15 ppm of CO as the fuel). Injecting a small amount of air into the anode stream, resulted in fast recovery of the lost current density (by injecting about 5% air into the fuel, 80% of the output current was recovered within 2 min at 53 ppm CO). Higher air bleeding ratio only resulted in minor improvement of the cell performance. Increasing the cell temperature; also using PtRu/C instead of Pt/C (at low temperatures) led to improving the cell performance. The use of PtRu/C at a high operating temperatures only resulted in minor improvement of the cell performance.

Abstract In this study, the effects of different non-uniform catalyst loading distributions that vary in both lateral and longitudinal directions on the performance of Polymer Electrolyte Membrane Fuel Cell (PEMFC) were numerically examined in detail. A two-phase, multi-component, transient and three-dimensional model was employed for simulating the performance of the cathode half-cell of the PEMFC. At the first step, the best longitudinal catalyst loading distribution was found. At the second step, several lateral distributions were superimposed to the noted longitudinal catalyst loading distribution and the performance of the PEMFC was evaluated for each distribution. Numerical results showed 3.1% enhancement for the longitudinal catalyst loading distributions; while 8% improvement was observed with a non-uniform catalyst loading distribution in both longitudinal and lateral directions. Results indicated that when lateral distribution is employed, liquid water saturation in the rib side is reduced. In the best longitudinal distribution, the ratio of platinum loading in longitudinal direction was 1.857 and the ratio of platinum catalyst from the center region of the catalyst layer to the rib side is varied in a wide range. In the case of the noted ratio more than 30, the enhancement in the PEMFC performance was insignificant. Finally, the effect of catalyst loading distribution was investigated on the polarization curves. It was found that the catalyst loading distribution is most effective at the high current densities while it has a minor effect at low current densities.

Abstract In this study, two-phase flow in a Polymer Electrolyte Membrane (PEM) fuel cell with the converging-diverging flow field was investigated using numerical simulation. A transient, three-dimensional, two-phase flow, and multi-component model, as well as an agglomerate model for oxygen reduction in the cathode catalyst layer, was employed to simulate the performance of the cathode half-cell. The numerical implementation was conducted by developing a new solver in OpenFOAM by the author. An augmentation about 28.2% was observed in the oxygen mass fraction at GDL/Channel interface for a PEM fuel cell with a converging-diverging angle of 0.3° in comparison with the reference cell (straight channels). Moreover, the average of liquid water saturation was decreased by 3.61% in the middle cross-section of gas channels and 9.4% near to the outlet region for reviewed converging-diverging cases. Finally, to investigate the improvement of the cell performance, polarization curve and net output power were presented. It was found that the using converging-diverging flow field was more effective at high current densities, while it had a minor effect at low current densities. The net output power of the PEM fuel cell with converging-diverging channels was enhanced by more than 10% compared with the base cell.