Tuning Mixed Nickel Iron Phosphosulfide Nanosheet Electrocatalysts for Enhanced Hydrogen and Oxygen Evolution

Highly efficient earth-abundant electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are of great importance for renewable energy conversion systems. Herein, guided by theoretical calculations, we demonstrate highly efficient water splitting in alkaline solution using quarternary mixed nickel iron phosphosulfide (Ni1–xFexPS3) nanosheets (NSs), even though neither NiPS3 nor FePS3 is a good HER (or OER) electrocatalyst. With tuned electronic structure and improved electrical conductivity induced by mixing appropriate amount of Fe into NiPS3, Ni0.9Fe0.1PS3 NSs display excellent HER activity (an overpotential of 72 mV vs reversible hydrogen electrode (RHE) at a geometric catalytic current density of −10 mA cm–2 and a Tafel slope of 73 mV dec–1), which is among the best HER catalysts under alkaline conditions. Ni0.9Fe0.1PS3 NSs also show a good apparent OER activity (an overpotential of 329 mV vs RHE at a catalytic current density of 20 mA cm–2 and a Tafel slope of 69 mV dec–1), although structural investigation indicates the formation of Ni(Fe)OOH and Ni(Fe)(OH)2 layers on the catalyst surface after OER reactions as likely the real active species. These mixed nickel iron phosphosulfide non-precious-metal electrocatalysts with enhanced intrinsic activity and long-term stability and durability should have great potential in overall water-splitting applications.