Fig. 3.

a Schematic diagram of conventional alkaline electrolyzer. Reproduced with permission from Ref. [68]. Copyright 2012 Elsevier Inc., b schematic diagram of the formation of the catalyst film, c schematic diagram of cathode deactivation caused by the deposition of trace metal impurities and the change of the overall voltage in the electrolytic cell. Reproduced with permission from Ref. [69]. Copyright 2018 Elsevier Inc