Nonmetallic Si Doping Constructs Cu ₂ O/Co–O–Si Tandem Sites for Neutral Nitrate Reduction Electrocatalysis Toward Ammonia Recovery and Energy‐Integrated Applications

Abstract

ABSTRACT The electrocatalytic nitrate reduction reaction (NO 3 RR) in neutral media is impeded by sluggish water dissociation and the lack of spatial coordination between distinct active phases. Here, we report a nonmetallic Si doping strategy to construct a Si‐CoCu@CF catalyst featuring a “Co–O–Si” interfacial bridge. This unique bonding motif not only regulates the in situ evolution of Cu 2 O but also establishes robust electronic communication between β ‑Co(OH) 2 and Cu 2 O, enabling a precisely engineered tandem catalytic cascade. The catalyst achieves a remarkable NH 3 yield rate of 26.6 mg h −1 cm −2 and a Faradaic efficiency (FE) of 97.9% at –1.0 V vs. RHE, maintaining stability for 25 h in a neutral electrolyte of 100 mM NO 3 – + 0.5 M Na 2 SO 4 . Mechanistic studies reveal a clear functional division: Cu 2 O governs the swift deoxygenation of NO 3 – to NO 2 – , while the “Co–O–Si” interface accelerates the Volmer step to enrich the surface with * H, promoting the subsequent hydrogenation of NO 2 – to NH 3 predominantly through a hydroxylamine pathway. The system further enables struvite recovery, energy‐saving methanol‐coupled electrolysis, and stable Zn‐NO 3 – battery operation. This work highlights the potential of nonmetallic elemental bridges in tandem electrocatalysis for integrated nitrate remediation and sustainable ammonia synthesis.