Inductive effects in cobalt-doped nickel hydroxide electronic structure facilitating urea electrooxidation

Abstract

Electrochemical oxidation of urea provides an approach to prevent excess urea emissions into the environment while generating value by capturing chemical energy from waste. Unfortunately, the source of high catalytic activity in state-of-the-art doped nickel catalysts for urea oxidation reaction (UOR) activity remains poorly understood, hindering the rational design of new catalyst materials. In particular, the exact role of cobalt as a dopant in Ni(OH)₂ to maximize the intrinsic activity towards UOR remains unclear. In this work, we demonstrate how tuning the Ni:Co ratio allows us to control the intrinsic activity and number of active surface sites, both of which contribute towards increasing UOR performance. We show how Ni₉₀Co₁₀(OH)₂ achieves the largest geometric current density due to the increase of available surface sites and that intrinsic activity towards UOR is maximized with Ni₂₀Co₈₀(OH)₂. Through density functional theory calculations, we show that the introduction of Co alters the Ni 3d electronic state density distribution to lower the minimum energy required to oxidize Ni and influence potential surface adsorbate interactions.

Keywords: DFT; Electrocatalysis; Electronic structure; Nickel-cobalt hydroxide; Sol-gel; Urea oxidation reaction.