Mechanistic Similarity in Catalytic N2 Production from NH3 and NO2- at Pt(100) Thin Films: Toward a Universal Catalytic Pathway for Simple N-Containing Species, and Its Application to in Situ Removal of NH3 Poisons

Understanding of the NH3 oxidation poisoning mechanism at Pt(100) is key to tackling a drawback of a reaction important to wastewater decontamination, electrochemical NH3 sensors, and NH3 fuel cells. Here we present a detailed study of poisoning adsorbates generated by NH3 at Pt(100) thin films and identify new key species (1) by comparison to NO2- reduction adsorbates and (2) using literature FTIR and DEMS (differential electrochemical mass spectrometry) data. We show that NH3 and NO2- generate identical intermediates at the same electrochemical potentials, suggesting that reactions as disparate as NH3 oxidation and NO2- reduction follow a universal catalytic pathway for N-containing compounds at Pt(100). This represents a significant paradigm shift from 45 years of thought that suggested the two pathways were completely separate. We then use the behavior of poisoning, adsorbed intermediates to develop an in situ cleaning procedure that allows improvements in performance and lifetime for NH3 electro-oxidation technologies. The in situ cleaning procedure, demonstrated for 1200 cleaning cycles over 2 h, required neither H-2 production nor Pt oxide formation. The latter trait allowed the employment of Pt(100) films without risk of immediate catalyst deorientation to a polycrystalline state.