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

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 (Co3O4) nanowires to boost their active sites, where phosphorus substitution for oxygen atoms greatly increases the number of cobalt (II) cations (Co2+) 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 VO alter the electron density of surface Co atoms in Co3O4 nanowires, resulting in the conversion of cobalt (III) cations (Co3+) to more active Co2+. As a result, the multifunctional catalysts of Co3O4 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.