Temperature optimization for improving polymer electrolyte membrane-water electrolysis system efficiency

Most of the hydrogen produced today is made using fossil fuels, making a significant contribution to global CO$_2$ emissions. Although polymer electrolyte membrane water-electrolyzers can produce green hydrogen by means of excess electricity generated from renewable energy sources, their operation is still not economical. According to industry experts, the necessary cost reductions can be achieved by 2030 if system efficiency can be improved. The commonly stated idea is to improve efficiency by increasing the stack temperature, which requires the development of more resistant materials. This study investigates not only the efficiency of an electrolysis cell, but of the entire electrolysis process, including gas compression of hydrogen. The results indicate that an optimal stack temperature exists for every operating point. It is shown that the optimal temperature depends solely on the electrode pressure and cell voltage and can be analytically calculated. In addition, the temperature optimization leads to significantly reduced hydrogen permeation at low current densities. In combination with the pressure optimization, the challenging safety issues of pressurized electrolysis can be eliminated for the entire load range and, at the same time, the efficiency of the overall system be maximized