Dynamic active sites on plasma engraved Ni hydroxide for enhanced electro-catalytic urea oxidation

Abstract

The urea oxidization reaction (UOR) is an important anodic reaction in electro-catalytic energy conversion. However, the sluggish reaction kinetics and complex catalyst transformation in electrocatalysis require activity improvement and better mechanistic understanding of the state-of-the-art Ni(OH)2 catalyst. Herein, by utilizing low-temperature argon (Ar) plasma processing, tooth-wheel Ni(OH)2 nanosheets self-supported on Ni foam (Ni(OH)2-Ar) are demonstrated to have improved UOR activity compared to conventional Ni(OH)2. The theoretical assessment confirms that the edge has a smaller cation vacancy formation energy than the basal plane, consequently explaining the structural formation. Operando and quasi-operando methods are employed to investigate the dynamic evolution of the Ni(OH)2 film in UOR. The crucial dehydrogenation products of Ni(OH)5O- intermediates are identified to be stable on the etched edge and explain the enhanced UOR in the low potential region. In addition, the dynamic active sites are monitored to elucidate the reaction mechanism in different potential ranges.