Fluorination-enabled Reconstruction of NiFe Electrocatalysts for Efficient Water Oxidation

Abstract

Developing low-cost and efficient electrocatalysts to accelerate oxygen evolution reaction (OER) kinetics is vital for water and carbon-dioxide electrolyzers. The fastest-known water oxidation catalyst, Ni(Fe)O_<i>x</i>H_<i>y</i>, usually produced through an electrochemical reconstruction of precatalysts under alkaline condition, has received substantial attention. However, the reconstruction in the reported catalysts usually leads to a limited active layer and poorly controlled Fe-activated sites. Here, we demonstrate a new electrochemistry-driven F-enabled surface-reconstruction strategy for converting the ultrathin NiFeO_<i>x</i>F_<i>y</i> nanosheets into an Fe-enriched Ni(Fe)O_<i>x</i>H_<i>y</i> phase. The activated electrocatalyst shows a low OER overpotential of 218 ± 5 mV at 10 mA cm^-2 and a low Tafel slope of 31 ± 4 mV dec^-1, which is among the best for NiFe-based OER electrocatalysts. Such superior performance is caused by the effective formation of the Fe-enriched Ni(Fe)O_<i>x</i>H_<i>y</i> active-phase that is identified by <i>operando</i> Raman spectroscopy and the substantially improved surface wettability and gas-bubble-releasing behavior.