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

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 mg_cat. ^-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.