Electrostatically robust CoFeOF nanosheet against chloride for green-H2 production in alkaline seawater electrolysis

Designing an inherently active and anti-corrosive catalyst to produce green hydrogen efficiently with a high stability is the key step in seawater splitting. Herein, a novel and highly active bifunctional electrode comprising CoFe-oxyfluorides (CoFeOF) nanosheets anchored on a nickel foam (NF) is designed via a simple hydrothermal route. The fabricated CoFeOF/NF electrode exhibits an exceptionally active and robust electrocatalysis in 1.0 M−based alkaline freshwater, artificial seawater, and natural seawater. In particular, the CoFeOF/NF electrodes drive the alkaline water electrolysis under 10 and 100 mAcm−2 at 236 and 280 mV (OER overpotential), 93 and 199 mV (HER overpotential) in freshwater; 230 mV and 290 mV (OER overpotential), 164 and 267 mV (HER overpotential) in artificial seawater; 220 and 280 mV (OER overpotential), 162 and 254 mV (HER overpotential) in natural seawater, respectively. More importantly, the two identical CoFeOF/NF || CoFeOF/NF electrode-based electrolyzer demonstrates a robust durability at a high current load of 400 mA.cm−2 for 145 h even in the natural seawater-based electrolyte. Based on this finding, it is anticipated that the highly electronegative oxygen and fluoride ions of the CoFeOF electrostatically suppress the highly corrosive chloride ions at the vicinity of the electrode, thereby inhibiting the corrosion of the CoFeOF/NF during the OER even at a high current load in seawater. This indicates the industrial potentiality of the CoFeOF/NF electrode in green-hydrogen generation sustainably via electrolysis of the abundantly available seawater.