Substitution-triggered broken symmetry of cobalt tungstate boosts redox kinetics in pseudocapacitive storage

Achieving delicate broken symmetry enables significant modification of crystals, from which a variety of property or performance modulation can be expected. Here, we report that the electrochemical performance of wolframite-type CoWO4 is significantly boosted using a Mo-substituted-W strategy. Experimental and theoretical analyses reveal that molybdenum substitution achieves WO6 coordination broken symmetry effectively, and it renders electroactive cobalt centers more polar, thus promoting the charge diffusion kinetics. Additionally, the enhancement of OH− adsorption energy can also alter the pseudocapacitive charge storage property, which significantly reinforces ion diffusion kinetics. As a result, the optimized molybdenum substitution (20 mol%) in CoWO4 exhibits a specific capacitance of 840 F g−1 at 1 A g−1, as well as a maximal energy density of 33.68 Wh kg−1 at power density of 800 W kg−1. Inspired by manipulating symmetry of crystals, our findings may provide insights into the origin of the substitution-promoted enhanced reaction kinetics.