Electronic modulation of VN on Co5.47N as tri-functional electrocatalyst for constructing zinc-air battery to drive water splitting

Developing effective strategy for constructing the electrocatalysts enable tri-functional electrocatalytic activity of hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is the premise to achieve both the zinc-air battery (ZAB) and overall water splitting. Herein, we utilize density functional theory to calculate the cobalt nitride (CoxN, x = 1, 2, 4, 5.47) system, revealing that the Co5.47N maybe exhibits a tri-functional activity due to the diverse valence states and high-density d-electron state of Co site. Furthermore, the electron of Co site is further delocalized by the electronic compensation effect of vanadium nitride (VN), thus improving the intermediates absorption and electrocatalytic activity. Accordingly, the Co5.47N/VN heterojunction is designed and synthesized via an electrospinning and a subsequent pyrolysis route. As expected, it displays excellent HER, OER, and ORR activity in alkaline electrolyte, which can be applied to assemble ZAB with a high power density of 207 mW/cm2 and overall water splitting system only requires a lower voltage of 1.53 V to achieve 10 mA/cm2. The electron regulation effect of VN makes the Co valence state decrease in the reduction reaction whereas increase in the oxidization reaction as evidenced by quasi-operando XPS analyses. Importantly, two ZABs connected in series could drive overall water splitting, indicating the potential application in renewable energy technologies.