p–d Orbital Hybridization in Ag‐based Electrocatalysts for Enhanced Nitrate‐to‐Ammonia Conversion

Abstract

Considering the substantial role of ammonia, developing highly efficient electrocatalysts for nitrate‐to‐ammonia conversion has attracted increasing interest. Herein, we proposed a feasible strategy of p‐d orbital hybridization via doping p‐block metals in an Ag host, which drastically promotes the performance of nitrate adsorption and disassociation. Typically, a Sn‐doped Ag catalyst (SnAg) delivers a maximum Faradaic efficiency (FE) of 95.5 ± 1.85 % for NH3 at ‐0.4 V vs. RHE and reaches the highest NH3 yield rate to 482.3 ± 14.1 mg h‐1 mgcat.‐1. In a flow cell, the SnAg catalyst achieves a FE of 90.2 % at an ampere‐level current density of 1.1 A cm‐2 with an NH3 yield of 78.6 mg h‐1 cm‐2, during which NH3 can be further extracted to prepare struvite as high‐quality fertilizer. A mechanistic study reveals that a strong p‐d orbital hybridization effect in SnAg is beneficial for nitrite deoxygenation, a rate‐determining step for NH3 synthesis, which as a general principle, can be further extended to Bi‐ and In‐doped Ag catalysts. Moreover, when integrated into a Zn‐nitrate battery, such a SnAg cathode contributes to a superior energy density of 639 Wh L‐1, high power density of 18.1 mW cm‐2, and continuous NH3 production.