Fluorination-enabled Reconstruction of NiFe Electrocatalysts\nfor Efficient Water Oxidation

Abstract

Developing low-cost and efficient electrocatalysts to accelerate\noxygen evolution reaction (OER) kinetics is vital for water and carbon-dioxide\nelectrolyzers. The fastest-known water oxidation catalyst, Ni­(Fe)­O_<i>x</i>H_<i>y</i>, usually produced\nthrough an electrochemical reconstruction of precatalysts under alkaline\ncondition, has received substantial attention. However, the reconstruction\nin the reported catalysts usually leads to a limited active layer\nand poorly controlled Fe-activated sites. Here, we demonstrate a new\nelectrochemistry-driven F-enabled surface-reconstruction strategy\nfor 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\nactivated electrocatalyst shows a low OER overpotential of 218 ±\n5 mV at 10 mA cm^–2 and a low Tafel slope of 31 ±\n4 mV dec^–1, which is among the best for NiFe-based\nOER electrocatalysts. Such superior performance is caused by the effective\nformation 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\nsurface wettability and gas-bubble-releasing behavior.