Realizing highly-efficient urea oxidation via decreasing the energy barrier of deprotonation over regulated electronic structure of Co doped Ni(OH)2

Abstract

Urea oxidation reaction (UOR) has been endorsed as an energy-saving approach for assisting hydrogen evolution, and Ni(OH)2-based catalysts has been widely used as efficient candidates for catalyzing UOR. However, the sluggish deprotonation process characterized by high energy barriers restricts the achievement of high efficiency. In this study, isoelectronic Co was introduced into Ni(OH)2 by one-step hydrothermal reaction. The doped Co induced electrons located on Ni centre, and decreased the redox potential of Ni2+/Ni3+. Consequently, the performance of Ni(OH)2 toward UOR was boosted, with the optimized 5 %Co-Ni(OH)2 exhibiting the lowest potential of 1.357 V vs RHE at 100 mA cm−2 and outstanding stability operating over 100 h at 10 mA cm−2. Moreover, a cell assembled by 5 %Co-Ni(OH)2/NF and Pt/C/NF outperformed better performance of urea electrolysis comparing with the commercial cell assembled by Pt/C/NF and RuO2/NF. Density functional theory (DFT) calculations revealed that the introduced Co regulated the electronic structure of Ni(OH)2, resulting in an optimized d-band centre. Moreover, the doped Co altered the initial adsorption coordination of urea molecules on NiOOH surface and reduced energy barrier for the consecutive deprotonation process (rate-determination step), which enhanced catalytic dynamic and subsequently led to a boosted performance toward UOR.