Modulation of oxygen vacancy and zero-valent zinc in ZnCr2O4 nanofibers by enriching zinc for efficient nitrate reduction

One-step generation and modulation of oxygen vacancies by enriching zinc to substitute chromium ions in ZnCr2O4 nanofibers are proposed to reduce nitrate to ammonia, which meanwhile induces the formation of zero-valent zinc. The catalyst with the most oxygen vacancies achieves an optimal NH3 yield rate of 20.36 mg h−1 mg−1cat. and Faradaic efficiency of 90.21 % at − 1.2 V vs. reversible hydrogen electrode (RHE), and it also has excellent long-term durability and structural stability. Theoretical calculations reveal oxygen vacancies are more favorable to form in ZnCr2O4, which shift the d-band center (εd) of Cr and Zn to higher and lower energy levels, respectively. The free energy for the whole reaction on ZnCr2O4 shows a continuous decreasing tendency, indicating the reaction can spontaneously take place. The results are expected to pave a new avenue to rationally design defective non-noble catalysts for catalyzing nitrate to produce ammonia.