Extending the accessibility of catalytic active sites through l-cysteine assisted sulfidation for promoting the hydrogen evolution reaction†

Green hydrogen production has been a particular focus in recent times for implementing sustainable fuels in the future energy economy. One of the most effective ways to produce clean and green hydrogen is electrocatalytic overall water splitting. Various researchers with their persistent explorations have made this topic, the research hotspot in understanding the catalysis mechanism and developing new novel materials. As the hydrogen evolution reaction (HER) kinetically limits the overall water splitting reaction, this work demonstrates the L-cysteine assisted synthesis of millerite nickel sulfide dispersed as particles on nickel foam (NS/NF) by a simple one-step hydrothermal process as a self-supported working electrode. The controlled phase of NiS is confirmed by XRD and TEM analysis and the size and morphology of the catalyst are characterised by SEM analysis. XAS analysis further explores the bulk structure and chemical coordination within the crystal system according to the XANES and EXAFS findings. The HER performance of the NS/NF catalyst exhibits superior activity to bare NF, requiring an overpotential of 140 mV to deliver a current density of −10 mA cm⁻² with a Tafel slope of 112.3 mV dec⁻¹. The catalyst demonstrated excellent durability for 50 h with further electro-activation of NS/NF under reduction conditions. In a two-electrode system, NS/NF||RuO₂ required only 1.79 V as the overall cell voltage to generate a current density of 10 mA cm⁻². This study illustrates a simple and facile route for NiS synthesis with extendable electrochemical surface area (ECSA), demonstrating superior HER activity over time, under alkaline conditions.