Au nanoparticles with oxygen vacancies on BiVO₄ for electrocatalytic nitrate reduction to ammonia

Ammonia (NH₃) is an important energy carrier and agricultural fertilizer. Development of electrocatalysts for efficient NH₃ electrosynthesis via the nitrate reduction reaction (NitRR) is highly desirable but remains a key challenge. In this work, we successfully loaded Au nanoparticles on BiVO₄ by a one-step hydrothermal method. It is demonstrated that by using Au nanoparticles (10-15 nm) embedded on BiVO₄ (Au/BiVO₄) with oxygen vacancies (Au loading is 1.3 wt%), the electrocatalytic NitRR is indeed possible under ambient conditions. Unexpectedly, at -1.35 V (vs. RHE), the yield rate for NH₃ of Au/BiVO₄ reached 3320.9 ± 89.9 μg h^-1 cm^-2, which was far superior to (11.3 μg h^-1 cm^-2) pristine BiVO₄. The ¹⁵N isotope labeling experiments confirmed that the produced NH₃ indeed originated from the nitrate reduction reaction catalyzed by Au/BiVO₄. The comprehensive analysis further confirms that the oxygen vacancies in Au/BiVO₄ can effectively weaken the N-O bonding and restrain the formation of by-products, resulting in high faradaic efficiency and NH₃ selectivity. Furthermore, in situ differential electrochemical mass spectrometry (DEMS) was adopted to monitor the electrochemical separation of the NitRR products on the surface of Au/BiVO₄.