Anodic Oxidation-Induced Interfacial Regulation of Nanoporous Co<sub>2</sub>P/CoOOH for Electrocatalytic Nitrate Reduction to Ammonia
Xinghao Sun, Yanqin Liang, Hui Jiang, Zhaoyang Li, Shuilin Wu, Zhonghui Gao, Zhenduo Cui, Guilan Fan, Shengli Zhu, Wence Xu
Abstract
The rechargeable Zn-nitrate battery presents a promising strategy for renewable energy conversion, ammonia production, and sewage treatment. Despite achieving excellent performance with transition metal-based electrocatalysts, the structure evolution of the electrocatalyst during Zn-nitrate battery charging/discharging and the corresponding reaction mechanism on nitrate reduction reaction (NO 3 RR) are still unclear. Inspired by the structural reconstruction in the charging process, nanoporous Co 2 P/CoOOH prepared by dealloying and anodic oxidation is reported as an electrocatalyst for NO 3 RR, achieving remarkable catalytic performance (ammonia yield rate: 1.93 mmol h –1 cm –2, Faradaic efficiency: 94.18%) with a high cathodic energy efficiency of 34.51%. Additionally, the assembled rechargeable Zn-nitrate battery delivers a power density of 31.99 mW cm –2 with a high charge–discharge stability. In-situ spectroscopy investigation reveals the generation of a Co 2 P/Co 3 O 4 heterosturcture through a synergetic redox reaction involving the cobalt species and nitrate ions during NO 3 RR, which enhances the approach of potassium-ionized water and improves ammonia generation kinetics by regulating the NO 2 – and *NH 2 generation. Density functional theoretical calculation further illustrates that Co 2 P/Co 3 O 4 heterostructure optimizes the adsorption of the *NO intermediate and enables an energetically favorable rate-limiting *NOH formation step. The unique structural evolution and nitrate activation mode of cobalt-based heterostructure would provide new insights on designing efficient electrocatalysts for nitrate reduction and rechargeable Zn-nitrate battery.