Kinetics and utilization studies of the oxygen reduction and hydrogen oxidation reactions in a proton exchange membrane fuel cell.

摘要

The current/voltage relation of a proton exchange membrane fuel cell (PEMFC) has been austerely studied through carefully designed experiments to support models developed theoretically using kinetic, thermodynamic and mass transport principles.; In order to develop a complete model description of voltage losses for a PEMFC gas phase mass transport free environment, individual experiments on; (i) the kinetics of the hydrogen oxidation reaction (HOR); (ii) the kinetic dependence of the oxygen reduction reaction (ORR), occurring on a PVC catalyst, on oxygen partial pressure and cell temperature; (iii) the voltage loss associated with proton transport and distribution of the oxygen reduction reaction in a porous proton exchange membrane fuel cell cathode; (iv) the effect of relative humidity, or water content, on the kinetics of the oxygen reduction reaction were performed.; These studies revealed that; (i) the voltage loss associated with the HOR is negligible due to its very high exchange current density (235--600 mA/cm2), (ii) the exchange current density, activation energy, and reaction order for the ORR are 2.5 x 10-8 A/cm2, 67 kJ/mol, and 0.5 respectively, (iii) the voltage loss resulting from a balance of proton transport and oxygen reduction reaction kinetics can be precisely predicted using a simple figure (4.2), which was developed from a solution to the conservation of charge equation in the cathode electrode and (iv) the effect of RH on ORR kinetics is negligible above 60% relative humidity. A PEMFC model that can accurately depict the voltage loss associated with each of the above material/process relationships was developed using differential cell experiments (i.e., experiments in which concentrations of reactants and products varied in only the through plane direction) and corresponding simplified 1-D models.