Urchin-like Al-Doped Co3O4 Nanospheres Rich in Surface Oxygen Vacancies Enable Efficient Ammonia Electrosynthesis.

Abstract

Developing cost-efficient electrocatalysts for ambient N2-to-NH3 conversion and revealing the reaction mechanism are appealing yet challenging tasks. Some transition metal oxides have been recently used to catalyze the nitrogen reduction reaction (NRR), but their further applications are greatly impeded because of their questionable conductivity, poor dispersion, limited active sites, and so forth. Herein, three-dimensional Ni foam-supported urchin-like Al-doped Co3O4 nanospheres rich in surface oxygen vacancies (Al-Co3O4/NF) were prepared via a hydrothermal process and subsequent annealing treatment. It is shown that introducing Al atoms into Co3O4 effectively tunes the electronic properties of the catalyst, and the increased surface oxygen vacancies induced by Al doping facilitate the activation of nitrogen. What is more, this urchin-like nanostructure, demonstrating an ability to limit the coalescence of gas bubbles, enables the rapid removal of small gas bubbles and better exposure of active sites to N2, thus yielding an impressive ammonia electrosynthesis activity (NH3 yield rate: 6.48 × 10-11 mol s-1 cm-2; Faradaic efficiency: 6.25%) in 0.1 M KOH. Electrochemical-based in situ Fourier transform infrared spectroscopy was employed to study the mechanism of NRR, indicating an associative alternating pathway.