20% STH achieved in solar-driven water electrolysis by forming a charge transfer path between LDH layers and optimizing oxygen absorption state in noble-metal-free NiFe-LDH electrodes

Abstract

Nickel–iron layered double hydroxide (NiFe-LDH) is widely recognized as a remarkable electrocatalyst for facilitating the oxygen evolution reaction (OER). However, its widespread application is hindered by poor electrical conductivity resulting from its large interlayer spacing and inefficient interlayer charge transport. To address these limitations, we developed a strategy that utilizes sulfur intercalation between LDH layers, creating NiFeS_x species between the LDH layers, which narrowed the interlayer spacing from 7.56 Å to 6.52 Å and enhanced the electron transferability of LDH by an order of magnitude. In addition, the NiFeS_x-LDH-NFs catalyst lowered the energy barrier for adsorbing oxygen-containing intermediates (OCIs) in the rate-determining step (RDS), thereby enhancing the OER activity. DFT, XAFS, and in situ Raman analyses revealed the characteristics of the NiFeS_x species in the NiFeS_x-LDH-NFs catalyst. Benefiting from these characteristics, the NiFeS_x-LDH-NFs catalyst showed superior bifunctional performance in an alkaline electrolyte, demonstrating low overpotentials (η) of 121 mV (HER) and 165 mV (OER) at 10 mA cm⁻². An outstanding solar-to-hydrogen (STH) efficiency of 20.01% was achieved using a photovoltaic-electrolysis (PVE) unit based on NiFeS_x-LDH-NFs and an GaInP₂/GaInAs/Ge solar cell under one-sun illumination, maintaining stable performance over 300 hours.