Dissecting the role of anions in surface reconstruction in urea oxidation to maximize assisted hydrogen production

Abstract

Transition metal chalcogenides (TMCs) are a category of electrocatalysts with favorable catalytic activity, however, the impact of oxidation and the leaching of chalcogens on the urea oxidation reaction (UOR) is not clear. Herein, 3D nanostructures of Mo-Ni₃S₂ nanowire arrays densely grown on nickel foam (NF) were conceived and produced using a hydrothermal treatment. During the UOR process, S and Mo are electrooxidized to generate sulfite (SO₃²⁻) and molybdate (MoO₄²⁻), with SO₃²⁻ further oxidized to sulfate (SO₄²⁻). Experiments proved that adding molybdate and sulfate actively improves the oxidation activity of Ni(OH)₂ and optimizes the adsorption/desorption of the UOR intermediates. The well-conceived Mo-Ni₃S₂ bifunctional catalyst performs well in urea-aided hydrolysis at up to 82 mA cm⁻² at a voltage of 1.57 V with little performance degradation over 50 h. A promising avenue for new insights into the mechanisms underlying anionic surface reconstruction in the UOR process is offered in this work.