Defects-Induced In-Plane Heterophase in Cobalt Oxide Nanosheets for Oxygen Evolution Reaction

Cobalt oxides as efficient oxygen evolution reaction (OER) electrocatalysts have received much attention because of their rich reserves and cheap cost. There are two common cobalt oxides, Co₃ O₄ (spinel phase, stable but poor intrinsic activity) and CoO (rocksalt phase, active but easily be oxidatized). Constructing Co₃ O₄ /CoO heterophase can inherit both characteristic features of each component and form a heterophase interface facilitating charge transfer, which is believed to be an effective strategy in designing excellent electrocatalysts. Herein, an atomic arrangement engineering strategy is applied to improve electrocatalytic activity of Co₃ O₄ for the OER. With the presence of oxygen vacancies, cobalt atoms at tetrahedral sites in Co₃ O₄ can more easily diffuse into interstitial octahedral sites to form CoO phase structure as revealed by periodic density functional theory computations. The Co₃ O₄ /CoO spinel/rocksalt heterophase can be in situ fabricated at the atomic scale in plane. The overpotential to reach 10 mA cm^-2 of Co₃ O₄ /CoO is 1.532 V, which is 92 mV smaller than that of Co₃ O₄ . Theoretical calculations confirm that the excellent electrochemical activity is corresponding to a decline in average p-state energy of adsorbed-O on the Co₃ O₄ /CoO heterophase interface. The reaction Gibbs energy barrier has been significantly decreased with the construction of the heterophase interface.