Molybdenum−Modified Titanium Dioxide Nanotube Arrays as an Efficient Electrode for the Electroreduction of Nitrate to Ammonia

Electrochemical nitrate reduction (NO3−RR) has been recognized as a promising strategy for sustainable ammonia (NH3) production due to its environmental friendliness and economical nature. However, the NO3−RR reaction involves an eight-electron coupled proton transfer process with many by-products and low Faraday efficiency. In this work, a molybdenum oxide (MoOx)-decorated titanium dioxide nanotube on Ti foil (Mo/TiO2) was prepared by means of an electrodeposition and calcination process. The structure of MoOx can be controlled by regulating the concentration of molybdate during the electrodeposition process, which can further influence the electron transfer from Ti to Mo atoms, and enhance the binding energy of intermediate species in NO3−RR. The optimized Mo/TiO2-M with more Mo(IV) sites exhibited a better activity for NO3−RR. The Mo/TiO2-M electrode delivered a NH3 yield of 5.18 mg h−1 cm−2 at −1.7 V vs. Ag/AgCl, and exhibited a Faraday efficiency of 88.05% at −1.4 V vs. Ag/AgCl. In addition, the cycling test demonstrated that the Mo/TiO2-M electrode possessed a good stability. This work not only provides an attractive electrode material, but also offers new insights into the rational design of catalysts for NO3−RR.