Vacancy enhanced proton preference in bimetallic phosphide catalysts for electrochemical ammonia synthesis and energy supply in Zn-NO3− battery

Abstract

Electrochemical ammonia synthesis via nitrate reduction reaction (NO3RR) under ambient condition is increasingly recognized as a sustainable alternative to the conventional Haber-Bosch process. Transition metal phosphides have attracted extensive attention as promising electrocatalysts owing to their unique proton provision. However, a challenge persists as the protons tend to dimerize to form H2 through the hydrogen evolution reaction (HER). In this work, we manipulate the proton preference in a Ni-Co bimetallic phosphide through vacancy engineering, leading to a notable enhancement in NH3 production. The developed NiCoP-VP with electron-rich surface demonstrates high selectivity, faradaic efficiency, and yield rate for ammonia, achieving a maximum yield rate of 16.63 mgNH3 h−1 cm−2 (ca. 83.17 mgNH3 h−1 mgcat.−1) at − 0.7 V vs. RHE. Density functional theory calculation reveal an increased energy barrier for proton dimerization and a more favorable rate-determining protonation step of *NO in NO3RR. Furthermore, a Zn-NO3− battery system was constructed based on NiCoP-VP, which showed dual functionality of generating electricity and producing NH3. With an open circuit voltage of 1.39 V and a peak-power density of 1.14 mW cm−2, the battery system presents a promising application for sustainable energy supply and green NH3 synthesis.