Urea electrolysis is an emerging approach for wastewater treatment and an attractive anodic process for electrochemical technologies. As a complex molecule, urea undergoes multistep oxidation with the formation of various products beyond the commonly assumed N₂ and CO₂. This concept article assesses recent efforts to decipher the reaction mechanisms and identifies the existing gaps, providing an outlook for the future design of UOR catalysts.

Abstract

Urea electrolysis is an emerging approach to treating urea-enriched wastewater and an attractive alternative anodic process to the oxygen evolution reaction (OER) in electrochemical clean energy conversion and storage technologies (e. g., hydrogen production and CO₂ electroreduction). While the thermodynamic potential for urea oxidation to dinitrogen is quite low compared to that of the OER, the catalysts reported to date require high overpotentials that far exceed those for the OER. Consequently, there is much room for improvement and rational catalyst design for the urea oxidation reaction (UOR). At the same time, due to the urea molecule having a more complex structure than water, UOR can lead to the formation of various products beyond the commonly assumed N₂ and CO₂. This concept article will critically assess recent efforts of the research community to decipher the formation mechanisms of UOR products focusing on the systematic analysis of the reaction selectivity. This work aims to analyze the current state of the art and identify existing gaps, providing an outlook for the future design of UOR catalysts with superior activity and selectivity by applying the knowledge of the molecular transformation mechanisms.