Heterojunction-enhanced electron transfer of copper nanoparticles promotes electrocatalytic ammonia synthesis from nitric oxide

Electrocatalytic nitric oxide (NO) reduction to ammonia (NH₃) serves as an innovative approach that concurrently addresses two pressing challenges: sustainable NH₃ synthesis through renewable pathways and environmental detoxification of hazardous nitric oxide. While the thermodynamic driving force of the electrocatalytic NO-to-NH₃ conversion (NORR) favors NH₃ generation, the system's practical viability is compromised by kinetically sluggish reaction pathways and the inherent solubility constraints of NO (1.93 mM in aqueous media at 25 ℃), with performance attenuation becoming progressively severe when the NO concentration decreases. However, an efficient copper-based catalyst that can effectively adsorb and activate NO is not yet available. Here, we have utilized the strategy of biphasic carriers to enhance MSI (metal-support interactions) to develop rutile-anatase titanium dioxide (TiO₂) heterojunction-supported copper nanoparticles (Cu@AR-TiO₂) as an effective catalyst for NORR. Under processing conditions of 10 % v/v NO, the NH₃-Faraday efficiency reached 91.38 % at -0.7 V vs. RHE, with the NH₃ yield rate achieving 393.73 μmol h^-1 mg^-1_cat at -0.8 V vs. RHE, surpassing counterparts devoid of heterojunction or copper nanoparticles. X-ray photoelectron spectroscopy and X-ray absorption spectroscopy shows that the three-phase interface formed by rutile-anatase TiO₂ (AR-TiO₂) heterojunction with copper nanoparticles (Cu NPs) enhanced the MSI of Cu NPs with the carrier to effectively promote the electron transfer from Cu NPs to carriers to form electron-deficient copper. In-situ Raman coupled with NO temperature-programmed desorption experiments revealed that the distinctive electron structure of Cu@AR-TiO₂ (copper nanoparticles supported by AR-TiO₂) strengthened the adsorption of NO and facilitated the generation of·NH₃ (ammonia being absorbed) intermediate, ultimately achieving superior catalytic efficiency in NH₃ production. This provides a novel approach to the design of NO-to-NH₃ catalysts.