Initiating an efficient electrocatalyst for water splitting via valence configuration of cobalt-iron oxide

[Display omitted] •Co2+-rich CoFe oxide was prepared from CoFe-PBA by a chemical tailoring process.•Co2+-rich CoFe oxide has superior OER and HER property to the well-balanced one.•Co2+ prefers higher adsorbing capacity and optimized reaction energy barriers. Engineering valence state of active center in non-noble metal-based electrocatalysts is of prime importance to enhance the performance for different catalytic reactions. However, studies on optimized valence configuration with extremely high activity remains a great challenge because of scanty chemical approaches. Herein, a kind of CoFe-oxide nanocubes with tunable valence composition was rationally designed for boosting water splitting electrocatalysis by partially chemical tailoring Prussian blue analogue. The resulting Co2+-rich CoFe-oxide nanocube (CoIIFe-ONC) exhibited higher OER and HER catalytic performance than the well-balanced CoFe-oxide. It demanded overpotentials of only 289 mV and 284 mV to drive a current density of 50 mA cm−2 for OER and HER in 1.0 M KOH, respectively. The DFT calculations revealed that CoIIFe-ONC is more favorable for OER and HER since the higher capacity of water adsorption, optimized route for electrons transferring, and lower energy barrier for water dissociation by the active valance configuration.