Efficient reduction of nitrate to Ammonia via TiO2-mediated interfacial electronic interactions in NiCoO2/TiO2/Ti heterojunction catalysts

Nitrate (NO 3 − ), as a major nitrogen oxide, is one of the principal contributors to global water pollution. The electrochemical nitrate reduction reaction (e-NO 3 RR) not only holds the promise of circumventing the environmental pollution issues associated with NO 3 − but also furthers the recycling of energy resources, paving the way for sustainable development. Herein, we have synthesized composite catalysts with a heterojunction between the bimetallic oxide (NiCoO 2 ) and titanium dioxide (TiO 2 ) on the surface of titanium foam (NiCoO 2 /TiO 2 /Ti) through a two-step reaction. This catalyst delivers a Faradaic efficiency (FE) of 94.1 % and the ammonia yield rate (NH 3 yield) nearing 200 μmol h −1  cm −2 in the e-NO 3 RR. After 24 h of reaction in a 0.1 M KNO 3 solution, the selectivity of NiCoO 2 /TiO 2 /Ti for ammonia (NH 3 ) can reach up to 94.9 %. In conjunction with density functional theory (DFT) calculations and electron spin resonance (ESR) experiments, it can be demonstrated that significant interfacial electronic interactions (IEIs) are established at the catalyst interface. Regulating the direction of internal electron transfer within the bimetallic oxide NiCoO 2 via TiO 2 enables the transformation of the NiCoO 2 surface from an electron-rich state to an electron-deficient state. This modulation alters the local electrochemical environment of NiCoO 2 , thereby enhancing its capability for NO 3 − adsorption and activation, and consequently facilitating the e-NO 3 RR process.