This review introduces the in-situ characterization techniques frequently used in the electrocatalytic NO₃ ⁻ reduction to NH₃ (ENO₃RA), summarizes five pathways for converting *NO to NH₃ during ENO₃RA on Cu-based catalysts. And the application of the in-situ techniques is presented as an example of Cu-based catalysts, which are sorted out in terms of composition and structure.

Abstract

The excess nitrate (NO₃ ⁻) in water mainly comes from agricultural fertilization and industrial wastewater, which breaks the nitrogen balance and poses a serious threat to the environment and human health. Driven by renewable energy, the electrocatalytic NO₃ ⁻ reduction to ammonia (NH₃) (ENO₃RA) is an environmentally friendly and sustainable technology. Due to its special structure, copper (Cu) is currently one of the best catalysts for ENO₃RA, but the reaction mechanism and the structure–activity relationships of catalysts are still not clear enough. In-situ characterization is a powerful tool to gain insight into the reaction process. This review introduces several types of in-situ techniques such as in-situ XAS, in-situ FTIR and in-situ DEMS, summarizes five pathways for converting *NO as the key intermediate to NH₃ during ENO₃RA on Cu-based catalysts. The research progress of Cu-based electrocatalysts in recent years is sorted out from the aspects of composition and structure, and the catalytic mechanisms are discussed with the help of in-situ characterization technologies. This review would be of help to provide reference characterization methods for exploring the mechanism and the design of electrocatalysts for ENO₃RA.