Controlling the Activity, Stability, and Regeneration of Copper-Chalcogenide Catalysts in Ammonia Electro-Oxidation

Abstract

This study explores innovative electrocatalysts for the selective electrochemical oxidation of ammonia to nitrogen, a crucial process in analytical and energy fields. Copper sulfides and selenides, synthesized via hydrothermal methods, were tested as electrocatalysts in alkaline conditions. Potentiodynamic measurements indicated that CuS demonstrated the highest activity for ammonia oxidation (5.8 mA/mg at 20 mV/s) compared to other catalysts. All catalysts predominantly produced N₂, with minor nitrite concentrations detected. However, CuS showed a dramatic 97% decrease in peak current density after 14 h of continuous operation. To recover its activity, sulfur-enrichment treatments were applied using Na₂S solutions. Chemical treatment successfully restored 90% of the lost activity, while electrochemical treatment nearly doubled the activity of the untreated electrode, reaching a peak current density of 19 mA/mg, comparable to platinum. XRD and XPS analyses revealed multiple copper oxidation states, highlighting the significance of Cu₂S and CuS in enhancing both activity and stability.