CoNi/Ba0.5Sr0.5Co0.8Fe0.2O3−δ/N-doped-carbon as a highly-active bifunctional electrocatalyst for water splitting

Perovskite-type oxides are considered as promising electrocatalysts to replace noble metals. Their electrochemical water splitting activity is, however, somewhat limited. This work reports a facile approach to promote the water splitting kinetics of a perovskite oxide, Ba0.5Sr0.5Co0.8Fe0.2O3−δ, by constructing a core-shell structured composite, CoNi/Ba0.5Sr0.5Co0.8Fe0.2O3−δ/N-doped-C, which couples Ba0.5Sr0.5Co0.8Fe0.2O3−δ with CoNi nanoparticles and N-doped-C. By this simple approach, the hydrogen evolution reaction inactive Ba0.5Sr0.5Co0.8Fe0.2O3−δ is transformed into a highly efficient catalyst (CoNi/Ba0.5Sr0.5Co0.8Fe0.2O3−δ/N-doped-C), which shows a small overpotential (0.18 V) to achieve a current density of 10 mA cm−2 in 1 M KOH. The CoNi/Ba0.5Sr0.5Co0.8Fe0.2O3−δ/N-doped-C also exhibits a remarkably high activity for oxygen evolution reaction in 1 M KOH solution. A small overpotential of 0.22 mV is demanded to drive a current density of 10 mA cm−2, which is superior to that of pristine Ba0.5Sr0.5Co0.8Fe0.2O3−δ and many state-of-the-art catalysts. An alkaline electrolyzer using CoNi/Ba0.5Sr0.5Co0.8Fe0.2O3−δ/N-doped-C as both electrodes delivers a current density of 10 mA cm−2 at a small operating voltage (1.64 V), much superior to a symmetric prototype using Ba0.5Sr0.5Co0.8Fe0.2O3−δ. Therefore, CoNi/Ba0.5Sr0.5Co0.8Fe0.2O3−δ/N-doped-C is among the best bifunctional catalysts for water splitting. More generally, this work opens new opportunities regarding designs of novel electrocatalysts and further improvements of state-of-the-art catalysts for various applications.