Polyoxometalate-modified AgAu nanoalloy electrocatalysts for highly efficient nitrate-to-ammonia conversion

Electrocatalytic nitrate(NO3-) reduction technology can simultaneously realize the remediation of nitrate pollution in water and distributed ammonia(NH3) synthesis. To meet the demand for efficient nitrate removal and ammonia resource recovery under practical water treatment conditions, it is of great significance to develop high-performance NO3- electroreduction catalysts suitable for near-neutral environments. However, the sluggish kinetics of multi-proton-coupled electron transfer in neutral media typically lead to unsatisfactory ammonia yields. To handle this issue, we design the lacunary polyoxometalate(POM)-modified Ag-Au nanoalloy catalysts supported by activated-carbon (10% AuAg-SiW9/C) to achieve efficient electrocatalytic conversion of NO3--to-NH3 under neutral conditions. The highly negative-charged SiW9 polyoxoanion effectively stabilized and dispersed the ultrafine AgAu alloy nanoparticles (~6 nm) through strong electrostatic repulsion. In 1 M phosphate buffer at pH ~7.4 containing 0.1 M KNO3, 10% AuAg-SiW9/C delivers a Faradaic efficiency (FE) of 95% and an NH3 yield rate of 1.3963 mg h-1 cm-2 at −0.6 V versus the reversible hydrogen electrode (RHE). The synergistic effect between the SiW9 polyoxoanions and Au alloying modulates the surface electronic structure of the Ag host via interfacial charge transfer. Density functional theory calculations elucidate that Au doping coupled with SiW9 incorporation reduces the energy barrier for the *NO → *NOH step to 0.46 eV, significantly facilitating this rate-determining step during the multistep hydrogenation process. This study confirms an effective electronic modulation strategy by coupling POMs modification and alloying effect for enhancing the NO3RR performance of metal-based electrocatalysts, providing new insights into the high-value conversion of nitrogen pollutants and the design of materials for electrochemical NH3 synthesis.