Engineering oxygen vacancies in CoO@Co3O4/C nanocomposites for enhanced electrochemical performances.

Efficient electrocatalyst materials for several applications, including energy storage and conversion, have become vitally for achieving technological. In this work, a CoO@Co3O4/C composites with abundant oxygen vacancies was successfully synthesized. The oxygen vacancies concentration was well controlled by changing the degree of vacuum during the heat treatment and was characterized by XPS and EPR. The existence of porosity structure arising from the cobalt oxides particles embedded in the carbon matrix provided an efficient charge and gas transmission path, significantly improving the performance of electrocatalytic oxygen evolution. Sufficient reactive sites were provided from both oxygen vacancies and heterogeneous interface. The mechanism of enhanced OER originates from the built-in electric field derived from oxygen vacancy was investigated. Consequently, the CoO@Co3O4/C composites offered an OER overpotential of 287 mV at a current density of 10 mA cm-2 with good stability in 1 mol L-1 KOH. In addition, combined with surface photovoltage (SPV), transient photovoltage (TPV), DFT, and In-situ Raman spectroscopy, the effect of oxygen defects on the electron migration ability and transformation of intermediate products were investigated to further understand the nature of catalytic activity in OER.