Ultralow FeIII Ion Doping Triggered Generation of Ni3S2 Ultrathin Nanosheet for Enhanced Oxygen Evolution Reaction

Abstract Oxygen evolution reaction (OER) is a sluggish process for water electrolysis to produce hydrogen fuel. In this work, ultralow level of Fe(III) ion triggered Ni 3 S 2 nanosheet grownon nickel foam (NF) for the enhanced electrocatalytic activity towards OER was reported for the first time. The OER electrocatalytic activity of the Fe(III)−Ni 3 S 2 /NF electrode was improved remarkably by adding only 2.1 (at.)% Fe(III) ion into the developed electrode and it merely requires an overpotential of η =213 mV to afford a current density of 10 mA cm −2 , significantly lower than both the Ni 3 S 2 /NF electrode (η=324 mV) and the benchmark RuO 2 /NF electrode (η=240 mV). As far as we know, this is the lowest overpotential to achieve the same value based on the reported Ni‐based sulfides. Meanwhile, the kinetic studies show that the Fe 2.1% −Ni 3 S 2 /NF electrode possessed a much smaller Tafel slope (33.2 mV dec −1 ) than that of Ni 3 S 2 /NF electrode (72.1 mV dec −1 ), demonstrating a fast reaction pathway. Further investigations attribute the enhanced OER activity to: ( i ) the addition of appropriate Fe(III) ions are favorable for the formation of interconnected Ni 3 S 2 ultrathin nanosheets, rather than keeping the original wrinkled fusiform nanorods, thus leading to a 2‐fold significantly enlarged electrochemical active surface areas,( ii ) the improved surface wettability can result in an enhanced compatibility and affinity of the catalyst with the electrode, which is good for gas bubble evolution and ( iii ) the enhanced intrinsic electrocatalytic activity due to the electronic structure regulating effect of Fe(III) lead to a fast shuttling of charge transfers during OER between the electrode and the solution.