Temperature-driven phase engineering: synergistic effect between NiS2 and MoS2 coupled with N-doped graphene self-supported on carbon cloth for efficient electrocatalytic seawater splitting

Abstract

The limited studies on Ni_xS_y as a bifunctional catalyst for seawater splitting have prompted the investigation of its charge mechanisms and address the research gap in phase transformation comprehension to maximize exposed active sites. Herein, a temperature-induced phase transformation of MoS₂–NiS₂ on nitrogen-doped graphene supported on a carbon cloth substrate (MSNS) was successfully conducted via a two-step hydrothermal and one-step sulfurization method. The optimum sample, MSNS-500 °C, exhibited a low overpotential and Tafel slope of 125 mV (63 mV dec⁻¹) and 190 mV (70 mV dec⁻¹) at a current density of 10 mA cm⁻² for the HER and OER, respectively, along with excellent faradaic efficiency exceeding 90% for the HER. The outstanding performance is attributed to the optimized phase transformation to form 1T/2H-MoS₂–NiS₂, which maximizes the exposure of active sites, enhances charge kinetics, and improves conductivity for seawater splitting. The uniform distribution of the MSNS particle size (∼50–55 nm), as evident from TEM and FESEM, ensured the consistent exposure of active sites, leading to more stable catalytic performance. This is depicted in the long-term stability of over 50 h at a current density of 50 mA cm⁻² in both simulated and natural seawater. Generally, this study presents an extraordinary bifunctional catalyst compared to those reported in the current available literature for the HER and OER.