Oxygen Vacancies‐Rich Metal Oxide for Electrocatalytic Nitrogen Cycle

Abstract

The development of industry and agriculture has been accompanied by an artificially imbalanced nitrogen cycle, which threatens human health and ecological environments. Electrocatalytic systems have emerged as a sustainable way of converting nitrogen‐containing molecules into high value‐added chemicals. However, the construction of high‐performance electrocatalysts remains challenging. The development of oxygen vacancy engineering strategy has promoted more research efforts to explore the structure‐activity relationship between catalytic activity and oxygen vacancies. This review systematically summarizes the recent development of oxygen vacancies‐rich metal oxides for electro‐catalyzing nitrogen cycling systems, involving electrocatalytic nitrate reduction reaction, nitric oxide reduction reaction, nitrogen reduction reaction, C─N coupling, urea oxidation reaction, and nitrogen oxidation reaction. First, the construction methods and characterization methods of oxygen vacancies are summarized. Then, the effect of oxygen vacancy on electrocatalytic activity of metal oxides is discussed in terms of regulating the electronic structures of electrocatalysts, improving the electroconductivity of catalysts, lowing the energy barrier, and strengthening adsorption and activation of intermediate species. Finally, future directions for oxygen vacancy engineering and electrocatalytic nitrogen cycle are anticipated.

Recent advances of metal suboxide catalysts for carbon‐neutral energy applications

“…106 Oxygen vacancies with structure disorder on the surface of TMO could act as highly active sites for catalytic reaction, which increased the density of states near the Fermi level, promoting efficient electron transfer and weakening the metal-oxygen bonds, producing a faster intermediate exchange effect that results in superior electrocatalytic performance. 11,34,106,107 Wang group reported an Vo-enriched CeO 2 , which were initially synthesized via a hydrothermal method and then subsequently realized with thermal treatment under a reduction atmosphere. 14 The signal intensity of oxygendeficient species with EPR signal at g = 2.035 is directly and linearly related to Vo concentration, which showed its increased with rising annealing temperature, and reached the highest intensity for Vo-CeO 2 -750, but dropped for Vo-CeO 2 -875 and Vo-CeO 2 -1000.…”

“…These factors can affect the level of oxygen vacancies and metal interstitials in the material, as well as alter the band structure and impurity energy levels. 11,22 3 | SYNTHETIC METHODS OF METAL…”

“…31,182,183 However, with the widespread use of nitrogen fertilizers, waste disposal and other human activities, large amounts of nitrogen are released into the natural environment, causing "nitrogen pollution" and endangering human health and the natural environment. To address this issue, nitrogen cycle technology has emerged involving NRR, 11,31 Selective C-N coupling toward electrocatalytic urea synthesis 14,184 and nitrate electroreduction to ammonia (NO x RR). 185,186 The fixation of dinitrogen to ammonia is a crucial chemical process as NH 3 is globally significant for the production of various economically profitable products.…”

“…188 Therefore, it is recommended to thoroughly examine the electrochemical system as well as the measurement environment for potential ammonia contamination. 11,191 In addition, Electrochemical reduction of nitrate pollutants to ammonia has also emerged as an attractive alternative for ammonia synthesis with the characteristic of higher water solubility and low bond energy of nitrate. 10,186 Additionally, urea is one of the most important nitrogen fertilizers in agriculture.…”

“…187 The electrocatalytic NRR has recently received significant attention as it enables artificial nitrogen fixation under ambient conditions. 11,189 However, the development of highly efficient electrocatalysts to alleviate the activation barrier in N 2 remains a challenge. Recently, metal suboxides have been extensively studied as an emerging catalyst owing to their unique and tunable electronic structure.…”