Synthesis of compositionally tunable, hollow mixed metal sulphide Co_xNi_yS_z octahedral nanocages and their composition-dependent electrocatalytic activities for oxygen evolution reaction

Abstract

Hollow nanostructures such as nanocages and nanoframes can serve as advanced catalysts with their enlarged active surface areas, and hence they have been of widespread interest. Despite the recent progress in the synthesis of this class of nanomaterials, hollow nanostructures with tunable compositions and controlled morphologies have rarely been reported. Here, we report a facile synthetic route to a series of compositionally tunable, hollow mixed metal sulphide (Co_xNi_yS_z) octahedral nanocages. The sulfidation of CoO octahedral nanoparticles generates CoO@Co_xS_y core-shell octahedra, and the in situ etching of the CoO core and annealing yield Co₉S₈ (pentlandite) octahedral nanocages (ONC). The addition of a Ni precursor during the etching/annealing process of CoO@Co_xS_y core-shell octahedra progressively yields hollow ONC structures of Co_9-xNi_xS₈, Ni₉S₈, Ni₉S₈/β-NiS, and Ni₃S₂/β-NiS via cation exchange reactions. Mixed cobalt/nickel sulphide, Co_9-xNi_xS₈ ONC, shows superior oxygen evolution reaction activity to monometallic sulphide ONC structures, demonstrating the synergy between different metal species.