Co₉S₈ core-shell hollow spheres for enhanced oxygen evolution and methanol oxidation reactions by sulfur vacancy engineering

Cobalt sulfides, especially Co9S8, have been widely studied as a potential earth-abundant electrocatalyst for many electrochemical reactions, such as oxygen evolution reaction (OER) and methanol oxidation reaction (MOR). However, the electrocatalytic performance of Co9S8 is not satisfactory because of its comparatively sluggish charge transport and reaction kinetics. Defect engineering and constructing hollow nanostructures are effective methods to improve their electrocatalytic performance, therefore, exploring an efficient route to obtain Co9S8 catalysts, simultaneously possessing sulfur vacancies and hollow nanostructure, is necessary. In this study, Co9S8-x core-shell hollow spheres with sulfur vacancies were prepared via a two-step solvothermal strategy, followed by thermal treatment under an H-2/Ar atmosphere. The content of sulfur vacancies can be regulated by varying the temperature during the thermal treatment. The obtained Co9S8-x core-shell hollow spheres exhibited interesting sulfur vacancy defect-dependent activity, one of which showed outstanding electrocatalysis performance for OER with an overpotential (eta) of 294 m V (at 10 mA cm(-2)) and MOR catalysis efficiency (164.9 mA cm(-2) at 1.8 V vs. RHE) in an alkaline medium. This study provides a promising and feasible pathway for developing efficient trifunctional electrocatalysts for renewable energy technologies.