Phase engineering of tungsten oxides support for boosting the NO₂^--to-NH₃ conversion over Cu₂O

Electrocatalytic nitrite reduction reaction (NO₂RR) has emerged as an attractive technique for NH₃ synthesis and nitrogen cycle regulation. Herein, Cu₂O catalysts supported on tungsten oxides with distinct crystal phases were controllably and innovatively developed for efficiently driving NO₂RR. Compared with monoclinic WO₃ and W₁₈O₄₉, hexagonal WO₃ possessed ample oxygen vacancies, which made for producing reactive H*. Reactive H* species were essential in the kinetics matching of deoxygenation/hydrogenation during NO₂RR. As expected, Cu₂O supported on hexagonal WO₃ nanowires (Cu₂O/h-WO₃ NWs) exhibited an outstanding activity (yield of 11.46 mg h^-1 mg_cat.^-1) and selectivity (Faradaic efficiency of 86.8%) for NH₃ synthesis, much superior to control catalysts. In/ex situ spectroscopic and electrochemical analyses revealed a higher H* adsorption capacity over Cu₂O/h-WO₃ NWs, which could timely desorb and migrate onto Cu₂O sites for driving NO₂RR. This work innovatively coupled phase engineering with dual-site catalysis, and established a kinetics matching among multi-step reactions in NO₂RR by tuning reactive H* dynamic equilibrium.