Covalent doping of Ni and P on 1T-enriched MoS2 bifunctional 2D-nanostructures with active basal planes and expanded interlayers boosts electrocatalytic water splitting

Abstract

The electrocatalytic water-splitting performance of MoS₂ nanostructures can be improved by increasing the edge density, activating basal planes, expanding the interlayer spacing and stabilizing the 1T-phase. In this work, for the first time, we have studied the synchronous involvement of all these driving factors to achieve the highest bifunctional performance of MoS₂ for water-splitting following doping and intercalation of nickel (Ni) and phosphorus (P) in a single-step reaction. Two nanostructures, nanoflowers (1T-Ni_0.2Mo_0.8S_1.8P_0.2 NFs, powder) for large scale synthesis and freestanding nanosheets on carbon-cloth (1T-Ni_0.2Mo_0.8S_1.8P_0.2 NS/CC) as binder-free electrodes, are fabricated. Co-doping of Ni and P enriches the 1T-phase, expands the interlayer spacing by 24%, activates basal planes significantly and increases the edge density of MoS₂ in the 2D-nanostructures. The 1T-Ni_0.2Mo_0.8S_1.8P_0.2 NS/CC and 1T-Ni_0.2Mo_0.8S_1.8P_0.2 NFs exhibit significantly low overpotentials of 55 and 99 mV at the current density of 10 mA cm⁻² for the hydrogen evolution reaction (HER) and 286 and 305 mV at 40 mA cm⁻² for the oxygen evolution reaction (OER), respectively. Further, 1T-Ni_0.2Mo_0.8S_1.8P_0.2-NS/CC (±) and 1T-Ni_0.2Mo_0.8S_1.8P_0.2-NF (±) alkaline electrolyzers require only 1.52 and 1.53 V, respectively, to generate a current density of 20 mA cm⁻² with robust stability, and are much superior to recently reported electrocatalysts, indicating the immense potential of the employed strategy for developing highly efficient and low-cost electrocatalysts for water-splitting.