Investigating the Effect of Water and Oxygen Distributions on Consistency of Current Density Using a Quasi-Three-Dimensional Model of a PEM Fuel Cell

Activation loss, mass transfer loss and ohmic loss are the three main voltage losses of the polymer electrolyte membrane fuel cell. While the former two types are relevant to concentration of oxygen in catalyst layer and the later one is associated with the water content in membrane. Distributions of water content and oxygen in a single cell are inconsistent which cause that current densities in each segment of the single cell are different. For the dry inlet gas, the water in the segments near the gas inlet channel will be carried to the segments near the gas outlet channel, which causes high ohmic loss of the segments near the gas inlet channel. In this work, a transfer non-isothermal quasi-three-dimensional model is developed to investigate inconsistency of current densities. Comprehensive physical and chemical phenomena inside the cell are included, especially the mass transfer of hydrogen, oxygen, vapor and liquid water in gas channels, gas diffusion layer and catalyst layer and non-frozen membrane water in ionomer. The results show that the distributions of water and oxygen significantly influence the distribution of current densities. For unsaturated humidity inlet gas, ohmic losses of the segments near inlet of the cathode gas channel are high, which leads to low current densities in these segments under high voltage conditions. Under low voltage conditions, the current densities of the segments in outlet of the cathode gas channel are low for low oxygen concentrations, causing mass transfer losses in these segments to increase. The counter-flow pattern shows a more consistency than the co-flow pattern.