Surface-engineered cobalt oxide nanowires as multifunctional electrocatalysts for efficient Zn-Air batteries-driven overall water splitting

Abstract Active sites engineering of electrocatalysts is an essential step to improve their intrinsic electrocatalytic capability for practical applications. Here, we demonstrate a facile surface phosphidisation into cobalt oxide (Co 3 O 4 ) nanowires to boost their active sites, where phosphorus substitution for oxygen atoms greatly increases the number of cobalt (II) cations (Co 2+ ) and oxygen vacancies (V O ) active sites. First-principles calculations combined with high-resolution X-ray photoemission spectroscopy, electron spin resonance and X-ray absorption spectroscopy characterization identify that the phosphorus heteroatoms and V O alter the electron density of surface Co atoms in Co 3 O 4 nanowires, resulting in the conversion of cobalt (III) cations (Co 3+ ) to more active Co 2+ . As a result, the multifunctional catalysts of Co 3 O 4 nanowires exhibit superior catalytic performance in overall water splitting with a low cell voltage of 1.61 V at 10 mA cm −2 and zinc-air batteries with a high open-circuit voltage of 1.41 V and power density of 72.1 mW cm −2 . Particularly, two-series-connected Zn-air batteries powerfully drive an electrolyzer system without any additional electrode materials. These experimental and theoretical findings offer a promising approach to constructing active sites in non-precious metal catalysts for efficient and stable electrocatalytic activity.