Interfacial Electronic Regulation in N-Doped Carbon-Encapsulated NiCo Alloy Enables High-Current Nitrate-to-Ammonia Electrosynthesis.

Abstract

Electrochemical nitrate reduction (NO3-RR) offers a route to couple wastewater remediation with green ammonia (NH3) synthesis, but remains kinetically and mechanistically challenging under high-current-density operation. Herein, an N-doped carbon-encapsulated NiCo alloy catalyst (NiCo@NC) is derived from a NiCo-ZB precursor supported on conductive carbon black. The cathodic NO3-RR over NiCo@NC achieves an NH3 yield rate of 187 mol h-1 gcat-1 with 95% Faradaic efficiency (FE) at -0.6 VRHE in an H-type cell and sustains ~92% FE at 2.0 A cm-2 under a cell voltage of 3.3 V in a membrane-electrode assembly. Pairing this cathodic NO3-RR with anodic methanol oxidation to formate enables simultaneous NH3 and formate production at 2.1 A cm-2 under a cell voltage of 2.8 V, while maintaining NH3 and formate FEs above 90% and 96%, respectively. In situ Fourier transform infrared and operando X-ray absorption fine structure spectra reveal preferential *NO stabilization and reversible Co valence/coordination, while theoretical calculations disclose interfacial charge polarization between NiCo alloy core and N-doped carbon shell, fabricating dual sites, comprising electron-deficient graphitic carbon and electron-rich pyridinic-N domains, that accelerate water dissociation/proton supply and lower the barrier of the rate-determining *NO → *NOH step. These insights establish alloy@NC interface regulation as a general strategy for high-rate NO3-RR.

Abstract as supplied by the indexing source. © the authors / publisher.