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

Abstract

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.