Ammonia Electrooxidation to Nitrite and Nitrate: Challenges and Insights

Ammonia is emerging as a promising hydrogen carrier. The electrochemical ammonia oxidation reaction (AmOR) offers a pathway to value‐added nitrite (NO 2 − ) and nitrate (NO 3 − ) and may serve as an alternative to the oxygen evolution reaction in electrolyzer systems. The aim of this study was to identify the key factors governing AmOR selectivity including the ammonia (NH 3 ) source, concentration, intermediate reactivity, and catalyst composition. Comparison between aqueous NH 3 and gaseous NH 3 supplied to a gas diffusion electrode was initially performed. The nitrite oxidation reaction (NO 2 − OR) was investigated as a key intermediate step toward complete NH 3 oxidation to NO 3 − . High‐throughput scanning droplet cell electrochemical measurements of thin‐film material libraries were used to discover novel AmOR catalyst. The results reveal that the ammonia concentration strongly affects product selectivity: High NH 3 concentrations suppress oxygen evolution and favor NO 2 − formation, whereas dilute NH 3 enables NO 3 − generation. Inductively coupled plasma mass spectrometry measurements confirm that NH 3 affects catalyst dissolution during AmOR.