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 performance 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 °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.