Revisiting Ammonia Oxidation Reaction on Polycrystalline Pt: A Rotating Ring Disk Electrode-Based Investigation

Abstract

Ammonia oxidation reaction (AOR) is investigated on polycrystalline Pt-disk and Pt-black catalysts in 0.1 M KOH in a rotating ring-disk electrode (RRDE) configuration in the potential range of 0.05–1.10 V (vs reversible hydrogen electrode, RHE). The effects of electrode porosity, ammonia concentration, convective mass transport, and the upper and lower potential limits of the voltammograms on AOR are investigated. The RRDE voltammograms in both NH3-free and NH3-containing supporting electrolytes, and chronoamperograms (CAs) with intermittent rotation at regular intervals, are recorded to understand the AOR mechanism and poisoning by the intermediates. A downshift of ∼60–70 mV (at ∼50 μA cm–2) in the onset potential of AOR is accompanied by a distinct downshift (∼130 mV) in the H adsorption/desorption peaks of the Pt {100} sites on increasing the NH3 concentration from 1.0 mM to 1.0 M. The results indicate that certain characteristic features observed in CA and RRDE voltammograms have contributions from the unintentional dissolved oxygen content in the bulk electrolyte.