Plasma‐Engraved Co₃O₄ Nanosheets with Oxygen Vacancies and High Surface Area for the Oxygen Evolution Reaction

Co 3 O 4 , which is of mixed valences Co 2+ and Co 3+ , has been extensively investigated as an efficient electrocatalyst for the oxygen evolution reaction (OER). The proper control of Co 2+ /Co 3+ ratio in Co 3 O 4 could lead to modifications on its electronic and thus catalytic properties. Herein, we designed an efficient Co 3 O 4 ‐based OER electrocatalyst by a plasma‐engraving strategy, which not only produced higher surface area, but also generated oxygen vacancies on Co 3 O 4 surface with more Co 2+ formed. The increased surface area ensures the Co 3 O 4 has more sites for OER, and generated oxygen vacancies on Co 3 O 4 surface improve the electronic conductivity and create more active defects for OER. Compared to pristine Co 3 O 4 , the engraved Co 3 O 4 exhibits a much higher current density and a lower onset potential. The specific activity of the plasma‐engraved Co 3 O 4 nanosheets (0.055 mA cm −2 BET at 1.6 V) is 10 times higher than that of pristine Co 3 O 4 , which is contributed by the surface oxygen vacancies.