Optimal operating parameters for advanced alkaline water electrolysis

Advanced zero-gap alkaline electrolyzers can be operated at a significantly higher current density than traditional alkaline electrolyzers. We have investigated how their perfor-mance is influenced by diaphragm thickness, temperature and pressure. For this a semi -empirical current-voltage model has been developed based on experimental data of a 20 Nm3/h electrolyzer. The model was extrapolated to thinner diaphragm thicknesses and higher temperatures showing that a nominal current density of 1.8 A cm-2 is possible with a 0.1 mm diaphragm at 100 degrees C. However, these operating parameters also lead to increased gas crossover, which limits the ability to operate at low loads. A gas crossover model has been developed, which shows that crossover is mainly driven by diffusive transport of hydrogen, caused by a high local supersaturation at the diaphragm surface. To enable a low minimum load of 10% the operating pressure should be kept below 8 bara.(c) 2022 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).

Automated summary

Advanced zero-gap alkaline electrolyzers can achieve higher current density by adjusting diaphragm thickness, temperature, and pressure. Thinner diaphragms and higher temperatures are found to enable higher current density, but also result in increased gas crossover.