Ionic Liquid-Assisted Synthesis of Nanoscale (MoS₂)_<i>x</i>(SnO₂)_1–<i>x</i> on Reduced Graphene Oxide for the Electrocatalytic Hydrogen Evolution Reaction

Abstract

Layered transition metal dichalcogenides (TMDs) have attracted increased attention due to their enhanced hydrogen evolution reaction (HER) performance. More specifically, ternary TMD nanohybrids, such as MoS_2(1-x)Se_2x or bimetallic sulfides, have arisen as promising electrocatalysts compared to MoS₂ and MoSe₂ due to their electronic, morphologic, and size tunabilities. Herein, we report the successful synthesis of few-layered MoS₂/rGO, SnS₂/rGO, and (MoS₂)_x(SnO₂)_1-x/rGO nanohybrids anchored on reduced graphene oxide (rGO) through a facile hydrothermal reaction in the presence of ionic liquids as stabilizing, delayering agents. Spectroscopic and microscopic techniques (electron microscopy, X-ray diffraction, Raman spectroscopy, neutron activation analysis, and UV-vis spectrophotometry) are used to validate the hierarchical properties, phase identity, and the smooth compositional tunability of the (MoS₂)_x(SnO₂)_1-x/rGO nanohybrids. Linear sweep voltammetry measurements reveal that incorporation of Sn into the ternary nanohybrids (as a discrete SnO₂ phase) greatly reduces the overpotential by 90-130 mV relative to the MoS₂ electrocatalyst. Significantly, the (MoS₂)_0.6(SnO₂)_0.4/rGO nanohybrid displays superior catalytic performance over MoS₂ alone, exhibiting a low overpotential (η₁₀) of 263 ± 5 mV and a small Tafel slope of 50.8 mV dec^-1. The hybrid catalyst shows high stability for the HER in acidic solutions, with negligible activity loss after 1000 cycles. The hierarchical structures and large surface areas possessing exposed, active edge sites make few-layered (MoS₂)_x(SnO₂)_1-x/rGO nanohybrids promising nonprecious metal electrocatalysts for the HER.