20% STH in solar driven water electrolysis by endowing 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) has been widely recognized as a remarkable electrocatalyst for facilitating oxygen evolution reaction (OER). However, its widespread application is hindered by poor electrical conductivity resulting from large interlayer spacing and inefficient interlayer charge transport. To address these limitations, we developed a strategy that utilizes sulfur intercalation between LDH layers, creating NiFeSx species between 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 NiFeSx-LDH-NFs catalyst lowered the energy barrier for adsorbing oxygen-containing intermediate (OCI) in the rate-determining step (RDS), thereby enhancing OER activity. DFT, XAFS, and in situ Raman revealed those characteristics of NiFeSx species in the NiFeSx-LDH-NFs catalyst. Benefiting from these merits, the NiFeSx-LDH-NFs catalyst shows superior bifunctional performance in 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 for 20.01% was achieved using a photovoltaic-electrolysis (PVE) unit based on NiFeSx-LDH-NFs and an InGaP2/GaInAs/Ge solar cell under one sun illumination, maintaining stable performance over 300 hours.