Decoupling the Pressure-Induced performance Gains in PEMFC stacks: Dominance of Charge-Transfer Resistance over a 10-200kPa Range

Abstract Appropriate operating conditions are considered one of the key factors for ensuring long-term stability, long lifetime, and high efficiency of proton exchange membrane fuel cells(PEMFCs). In this study, the influence of gas inlet pressure on the performance, high-frequency resistance (HFR), impedance, and flow resistance of a PEMFC stack is systematically investigated over a wide pressure range of 10–200 kPa. The experiments are conducted on an 8-cell stack (containing 3 active cells and 5 dummy cells). The operating conditions are controlled at a current density of 1000 mA/cm², a gas relative humidity of 40%, and a cell temperature of 70°C, while the gas pressure is gradually adjusted, and its effects on various indicators are analyzed. The results indicate that the cell performance is significantly improved by increasing the gas pressure; however, the performance gain is first increased and then diminished. Specifically, the average voltage is increased by 69 mV when the pressure is raised from 30/30 to 100/100 kPa, but only by 12 mV when the pressure is further increased from 100/100 to 200/200 kPa. The performance improvement induced by pressure is attributed to the optimization of reversible voltage, ohmic resistance, charge transfer resistance, and mass transfer resistance, among which the most significant contribution is made by the reduction in charge transfer resistance.