Recent advances in electrocatalysts for electro-oxidation of ammonia

Abstract

The electro-oxidation of ammonia has attracted much attention in recent years since it addresses both the clean energy supply free of CO_x and environmental protection. However, the large-scale applications of ammonia electro-oxidation technologies have been strongly hindered by the insufficient performance and the high cost of the electrocatalysts related to the usage of high Pt loadings. Therefore, considerable effort has been devoted to developing electrocatalysts for ammonia electro-oxidation with improved activity and lower Pt loading over the past 10 years. From the initial focus on pure metal electrocatalysts, a wide range of Pt-based and Pt-free electrocatalysts for ammonia electro-oxidation have been investigated. This review begins with a brief discussion on the mechanism of the ammonia electro-oxidation with particular attention on the latest findings on the active intermediates and poisoning species, which is important for the fundamental understanding of the principles of improving the electrocatalyst performance for ammonia electro-oxidation. Typical types of electrocatalysts for ammonia electro-oxidation are next described, including pure metal, Pt alloy and Pt-free electrocatalysts. The various preparation methods are discussed and related to the resulting structures and electrocatalytic properties for ammonia electro-oxidation. The factors influencing the performance of the electrocatalysts are also highlighted for gaining fundamental insight into the optimization of the electrocatalyst performance. Based on the results achieved in this area, several future research directions are finally proposed and discussed.