High-Efficiency Ammonia Electrosynthesis on Anatase TiO2–x Nanobelt Arrays with Oxygen Vacancies by Selective Reduction of Nitrite

Electrocatalytic reduction of nitrite to NH3 provides a new route for the treatment of nitrite in wastewater, as well as an attractive alternative to NH3 synthesis. Here, we report that an oxygen vacancy-rich TiO2–x nanoarray with different crystal structures self-supported on the Ti plate can be prepared by hydrothermal synthesis and by subsequently annealing it in an Ar/H2 atmosphere. Anatase TiO2–x (A-TiO2–x) can be a superb catalyst for the efficient conversion of NO2– to NH3; a high NH3 yield of 12,230.1 ± 406.9 μg h–1 cm–2 along with a Faradaic efficiency of 91.1 ± 5.5% can be achieved in a 0.1 M NaOH solution containing 0.1 M NaNO2 at −0.8 V, which also exhibits preferable durability with almost no decay of catalytic performances after cycling tests and long-term electrolysis. Furthermore, a Zn–NO2– battery with such A-TiO2–x as a cathode delivers a power density of 2.38 mW cm–2 as well as a NH3 yield of 885 μg h–1 cm–2.