Cactus-Like Hollow Cu_{2- x}S@Ru Nanoplates as Excellent and Robust Electrocatalysts for the Alkaline Hydrogen Evolution Reaction

The development of Pt-free electrocatalysts for the hydrogen evolution reaction (HER) recently is a focus of great interest. While several strategies are developed to control the structural properties of non-Pt catalysts and boost their electrocatalytic activities for the HER, the generation of highly reactive defects or interfaces by combining a metal with other metals, or with metal oxides/sulfides, can lead to notably enhanced catalytic performance. Herein, the preparation of cactus-like hollow Cu_{2- x}S@Ru nanoplates (NPs) that contain metal/metal sulfide heterojunctions and show excellent catalytic activity and durability for the HER in alkaline media is reported. The initial formation of Ru islands on presynthesized Cu_1.94S NPs, via cation exchange between three Cu⁺ ions and one Ru³⁺, induces the growth of the Ru phase, which is concomitant with the dissolution of the Cu_1.94S nanotemplate, culminating in the formation of a hollow nanostructure with numerous thin Ru pillars. Hollow Cu_{2- x}S@Ru NPs exhibit a small overpotential of 82 mV at a current density of −10 mA cm⁻² and a low Tafel slope of 48 mV dec⁻¹ under alkaline conditions; this catalyst is among state-of-the-art HER electrocatalysts in alkaline media. The excellent performance of hollow Cu_{2- x}S@Ru NPs originates from the facile dissociation of water in the Volmer step.