Correlative in situ analysis of the role of oxygen on ammonia electrooxidation selectivity on NiOOH surfaces

The electrochemical ammonia oxidation reaction (AOR) offers a promising pathway for environmental remediation, energy conversion, and the production of value-added chemicals. Although NiOOH shows potential as an efficient catalyst for AOR, the underlying mechanism and the influence of the concurrent oxygen evolution reaction (OER) are not yet fully understood. Here, the AOR mechanism on NiOOH is examined, emphasizing the influence of OER and dissolved O 2 . Using differential electrochemical mass spectrometry (DEMS), Raman spectroelectrochemistry, UV–vis spectroelectrochemistry, and attenuated total reflection infrared reflection (ATR-IR) spectroelectrochemistry, we reveal that the NiOOH formation, AOR activity, selectivity, and deactivation as well as the reaction intermediates are significantly modulated by OER and dissolved O 2 . AOR on NiOOH is potential-dependent: N 2   production starts with the onset of OER, while extensive NO x and NO 2/3 − species form at higher potentials. The OER competes with the AOR-to-N 2 pathway but promotes AOR-to-NO x , where the presence of O 2 mitigates OER deactivation on NiOOH. Our findings highlight the advantage of correlative in situ analysis in studying electrocatalytic processes and advance the current understanding of AOR pathways on NiOOH toward energy and environmental applications.