Construction of tetrahedral CoO4 vacancies for activating the high oxygen evolution activity of Co3−xO4−δ porous nanosheet arrays

Abstract

This study presents low-crystalline and non-stoichiometric cobalt oxide (Co_3−xO_4−δ) porous nanosheet arrays (PNAs) grown on carbon fiber cloth (CFC) (Co_3−xO_4−δ PNAs/CFC) by a facile in situ anodic oxidation strategy. We firstly verified that the above prepared low crystalline cobalt oxide contained tetrahedral CoO₄ vacancies, resulting in the creation of O vacancies at adjacent octahedral CoO₆ sites, allowing the generation of tetragonal–pyramidal CoO₅ sites which were regarded as active sites and being accessible for the oxygen evolution reaction (OER) with different reaction mechanisms compared to that of traditional CoO₆ sites in high-crystalline and stoichiometric Co₃O₄, thus endowing Co_3−xO_4−δ PNAs/CFC with significantly improved OER activity and superior stability compared to their crystalline counterparts (Co₃O₄ PNAs/CFC), as illustrated by experiments and density functional theory (DFT) calculations. This study will open up a new approach for the synthesis of defect-rich materials and provide new insight into the structure–property relationship of OER catalysts.