Relating Selective Electrochemical Nitrate Reduction to Electronic Structure by AP-XPS

Abstract

Ammonia produced by the Haber-Bosch process fixes nitrogen by sourcing hydrogen from methane steam reforming—today’s most carbon intensive industrial process. Alternatively, ammonia can be produced electrochemically from industrial waste nitrogen sources (e.g. nitric oxides, and nitrate), sourcing protons from water and electrons as reducing agents. However, reduction of such oxidized nitrogen species involves complex reaction mechanisms where the stability of critical reaction intermediates (e.g. nitric oxide) dictates selectivity towards ammonia as a final product. Inspired by Hammer and Nørskov’s d-band theory, we utilize synchrotron-based ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) to explore the adsorption affinity, and ability of a surface to dissociate, nitric oxide for a series of transition metals (Fe, Co, Ni, Cu). Nitric oxide adsorption affinity and dissociation are then linked to transition metal electronic structure and contextualized further with ex-situ electrochemical selectivity measurements and density functional theory (DFT) calculations.