Efficient NiFe-based oxygen evolution electrocatalysts and origin of their distinct activity

Efficient oxygen evolution reaction (OER) electrocatalyst is essential for water electrolysis. Herein, high-performance NiFe-based layered double hydroxides (LDH), phosphide and sulfide OER pre-catalysts were fabricated and their distinct activity was unveiled. The as-prepared NixFe1−xS exhibits ultralow OER overpotential of 122 mV at 10 mA cm−2 in 1 M KOH. The alkali-electrolyzer using NixFe1−xS electrodes achieve superior performance exhibiting a voltage of 1.46 V at 10 mA cm−2. Experimental analysis reveals that, during OER, Fe dissolution into electrolyte occurs for NiFe LDH and NixFe1−xP, which were both converted into NiOOH, well explaining their similar activity. Interestingly, Fe dissolution is significantly mitigated in NixFe1−xS, forming partially oxidized Fe2O3/FeOOH species. Theoretical calculations confirmed that Fe2O3/FeOOH is responsible for the enhanced OER energetics of NixFe1−xS. These observations provide new insights on the distinct activity of NiFe-based electrocatalysts, guiding their rational design as well.