Hydrogen crossover in proton exchange membrane electrolysers: The effect of current density, pressure, temperature, and compression

In this paper, the hydrogen crossover through the membrane, which is a major concern from the safety, durability, and efficiency viewpoints, in proton exchange membrane (PEM) electrolysers, is investigated. It is well-documented that hydrogen crossover rate increases by pressure, temperature, and current density. However, how current density affects the hydrogen crossover rate is yet to be fully understood. The effect of current density on hydrogen crossover is usually attributed to hydrogen supersaturation and enhanced hydrogen pressure on the membrane due to the pressure drop through the catalyst layer and liquid/gas diffusion layer (LGDL). However, other parameters, as suggested by recent research studies, can have an important role to play. Here, by developing an analytical model, the effects of several parameters are investigated. The findings from this study suggest that hydrogen crossover is affected by the increase in the membrane temperature, hydrogen supersaturation, and compression of the LGDL. The effect of membrane temperature increase with current density on hydrogen crossover was found to be pronounced at current densities above 2 A cm−2. The increase in hydrogen supersaturation with current density was found to be the main cause of hydrogen crossover during electrolysis. Stack compression increases the hydrogen crossover rate mainly by reducing the mass transfer coefficient and hence the hydrogen supersaturation. The effect of increased hydrogen pressure on the membrane is more noticeable at low operating pressures; however, in general, does not have a major impact on the hydrogen crossover. It is also suggested that the hydrogen length of the diffusion path should also include the ionomer of the CL in addition to the membrane thickness. The findings of this research help with a better understanding of the hydrogen crossover during PEM electrolysis that can be considered during material selection and design of the cell components. This helps with reducing the crossover rate to improve efficiency and durability and ensure safe operations.