Structure sensitivity of ammonia electro-oxidation on transition metal surfaces: A first-principles study

Abstract

Ammonia electro-oxidation is a promising catalytic reaction for application in alkaline fuel cells. Here, we study the trends in this reaction on the (100) facet of eight fcc transition metals: Au, Ag, Cu, Pt, Pd, Ni, Ir, and Rh. We calculate from first-principles (DFT-GGA-PW91) the energetics for two mechanisms: (i) the N + N mechanism and (ii) the Gerischer-Mauerer mechanism. The onset potentials for both mechanisms are provided for both (100) and (111) facets. We also calculate the activation energies for the N-N bond-making non-Faradaic events on Cu, Pt, Pd, Ni, Ir, and Rh. We discover that N* – which is considered a poison for Pt(111) – is a reactive intermediate on Pt(100), allowing for a facile dimerization to N2 on Pt(100) at high potentials. We draw similar analyses for the structure sensitivity on the other metals, and we conclude with some general principles to guide catalyst design for this reaction.