Manifold improvement of water oxidation activity of NaCoO2 by selective cation exchange

Water oxidation produces electrons, protons, and oxygen, essential components in fuel production processes like CO₂ reduction and hydrogen generation. To date, less cost and more-abundant catalysts showed low activity for the water oxidation reaction. Herein, we developed a simple and effective way to selectively exchange Na⁺ with H⁺ in NaCoO₂ and created high surface area layered materials for efficient water oxidation. The photochemical water oxidation reaction activity improved from 0.9 × 10^?3 s^?1 (pristine NCO) to 2.90 × 10^?3 s^?1 (AT-NCO-2M). The electrochemical overpotential decreased from 600 to 370 mV, and the Tafel slope dropped from 93 to 47 mV/dec. Enhanced water oxidation activity is owing to delamination of stacked layered structure into few layer structure, increased surface area, super hydrophilic nature, and coexistence of Co⁴⁺ and Co³⁺ species. Our findings show the importance of the exchange of Na⁺ with H⁺ in Na-based metal oxides for efficient water oxidation.