Unveiling Active Sites in Feooh Nanorods@Niooh Nanosheets Heterojunction for Superior Oer and Her Electrocatalysis in Water Splitting

Abstract

The development of cost-effective, highly active, and stable electrocatalysts for water splitting to produce green hydrogen is crucial for advancing clean and sustainable energy technologies. Herein, we present an innovative in-situ synthesis of FeOOH nanorods@NiOOH nanosheets on nickel foam (FeOOH@NiOOH/NF) at an unprecedentedly low temperature, resulting in a highly efficient electrocatalyst for overall water splitting. The optimized FeOOH@NiOOH/NF sample, evaluated through time-dependent studies, exhibits exceptional oxygen evolution reaction (OER) performance with a low overpotential of 261 mV at a current density of 20 mA cm-2, alongside outstanding hydrogen evolution reaction (HER) activity with an overpotential of 150 mV at a current density of 10 mA cm⁻², demonstrating excellent stability in alkaline solution. The water-splitting device featuring FeOOH@NiOOH/NF-2 electrodes achieve a voltage of 1.59 V at a current density of 10 mA cm-2, rivaling the state-of-the-art RuO₂/NF||PtC/NF electrode system. Density functional theory (DFT) calculations unveil the efficient functionality of the Fe sites within the FeOOH@NiOOH heterojunction as the active OER catalyst, while the Ni centers are identified as the active HER sites. The enhanced performance in OER and HER is attributed to the tailored electronic structure at the heterojunction, modified magnetic moments of active sites, and increased electron density in the dx2-y2 orbital of Fe. This work provides critical insights into the rational design of advanced electrocatalysts for efficient water splitting.

Keywords: FeOOH nanorods@NiOOH nanosheets, Heterojunction, overall water splitting, Electrocatalyst, Electronic properties