Performance analysis of polymer-electrolyte water electrolysis cell at a small-unit test cell and performance prediction of large stacked cell

Recently the hydrogen energy system has been proposed as a countermeasure for the depletion of fossil fuel and global warming. The polymer electrolyte electrolysis cell (PEEC) can efficiently produce pure hydrogen under high current density. To design a PEEC properly and to optimize its operating conditions we have measured and analyzed the PEEC performance. Using measured overpotentials we have made a two-dimensional simulation code for PEEC. Calculated results show that the profile of current density and temperature are constant along the water flow direction, because the exothermic heat from overpotentials is almost canceled out by the endothermic heat of both entropy change and evaporation, and by heat transfer to the constant-temperature separators, resulting in a constant water-electrolyzing potential along the flow direction. The current densities measured at a segmented-electrode cell agreed well with the calculated values. By applying this simulation code to a large unit-cell with adiabatic boundary conditions, we have predicted the performance of a large stacked PEEC having an electrode length of 1 m. The predicted cell temperature and current density increase only a little along the flow direction. Under operating conditions with high pressure, the endothermic heat of water evaporation decreases greatly and the cell temperature is apt to increase downstream compared to the atmospheric operation.