In Situ Formation of Surface-Induced Oxygen Vacancies in Co(9)S(8)/CoO/NC as a Bifunctional Electrocatalyst for Improved Oxygen and Hydrogen Evolution Reactions

Creating oxygen vacancies and introducing heterostructures are two widely used strategies in Co-based oxides for their efficient electrocatalytic performance, yet both strategies have rarely been used together to design a bifunctional electrocatalyst for an efficient overall water splitting. Herein, we propose a facile strategy to synthesize oxygen-defect-rich Co(9)S(8)/CoO hetero-nanoparticles with a nitrogen-doped carbon shell (ODR-Co(9)S(8)/CoO/NC) through the in situ conversion of heterojunction along with surface-induced oxygen vacancies, simply via annealing the precursor Co(3)S(4)/Co(OH)(2)/ZIF-67. The as-prepared ODR-Co(9)S(8)/CoO/NC shows excellent bifunctional catalytic activities, featuring a low overpotential of 217 mV at 10 mA cm(−2) in the oxygen evolution reaction (OER) and 160 mV at 10 mA cm(−2) in the hydrogen evolution reaction (HER). This performance excellency is attributed to unique heterostructure and oxygen defects in Co(9)S(8)/CoO nanoparticles, the current work is expected to offer new insights to the design of cost-effective, noble-metal-free electrocatalysts.