Co 3 O 4−δ Quantum Dots As a Highly Efficient Oxygen Evolution Reaction Catalyst for Water Splitting

Co 3 O 4−δ quantum dots (Co 3 O 4−δ -QDs) with a crystallite size of approximately 2 nm and oxygen vacancies were fabricated through multicycle lithiation/delithiation of mesoporous Co 3 O 4 nanosheets. Used as an oxygen evolution reaction (OER) electrocatalyst for water splitting, the catalytic performance (an overpotential of 270 mV@10 mA cm –2 and no decay within 30 h) of Co 3 O 4−δ -QDs is superior to that of previously reported Co-based catalysts and the state-of-the-art IrO 2 . Compared to that of the Co 3 O 4 nanosheets, the enhanced OER activity of Co 3 O 4−δ -QDs is attributed to two factors: one is the increased quantity of the Faradaic active sites, including the total active sites ( q * Total ), the most accessible active sites ( q * Outer ), and their ratio ( q * Outer / q * Total ); the other is the enhanced intrinsic electroactivity per active site evaluated by the turnover frequency and the current density normalized by the most accessible active sites ( j / q * Outer ) related to the OER. This multicycle lithiation/delithiation method can be applied to other transition metal oxides as well, offering a general approach to develop high-performance electrocatalysts for water splitting.