Influence of Surface Chemistry of Iron-Nickel Oxide Films on Ammonia Synthesis and Hydrogen Production

Abstract

The Faradaic efficiency limitation of electrocatalyst surfaces for low temperature nitrogen reduction to ammonia in aqueous electrolytes is driven by a dominance of the hydrogen evolution reaction (HER). To address and reduce the dominance of the HER on electrocatalyst surfaces, along with maintaining electrocatalyst activity toward the nitrogen reduction reaction (NRR), control of both the electrocatalyst surface and the electrolyte interface chemistry are likely necessary. In this work, we study how the surface chemistry of a suite of iron-nickel oxide electrocatalysts changes upon exposure to the NRR electrocatalytic environment and as a function of as-synthesized chemical structure. In addition, we study how an electrolyte interface functional layer influences both electrocatalyst surface chemistry and resulting electrocatalytic behavior toward the HER and the NRR. Characterization focuses on the use of traditional ultra-high vacuum and ambient pressure x-ray photoelectron spectroscopy (XPS) experiments to understand the details of as-synthesized, post-electrochemistry, and ambient exposure (i.e., water vapor and argon/nitrogen gas exposed) surface chemistry of the iron-nickel oxide films. A discussion of our experimental results will include an analysis of how surface composition, metal component oxidation state, electrolyte components, and water/hydroxyl surface adsorption change as a function of starting film composition and ambient exposure conditions.