Efficient nanointerface hybridization in a nickel/cobalt oxide nanorod bundle structure for urea electrolysis

Abstract

Urea electrolysis has received great attention for the energy-relevant applications, and efficient nanostructured catalysts are required to overcome the sluggish urea oxidation kinetics. Herein, we noticed that the valence state of Ni in the hybrid Ni/Co oxide nanorods can be correlated to the catalytic capability for urea oxidation. Crystal lattice hybridization was found in the interface of Ni/Co oxide nanoparticles that assembled as a nanorod bundle structure. The more or the less of Ni²⁺/Ni³⁺ generated lower catalytic ability, and Ni/Co oxide with the optimum content of Ni²⁺/Ni³⁺ exhibited the highest catalytic ability for urea oxidation because of the efficient synergism, resulting from the formation of high valence state of Ni species and improved kinetics. A low onset potential of 1.29 V was required for the urea oxidation compared with the high onset potential of 1.52 V for water oxidation; high selectivity for urea oxidation was found in the potential below 1.50 V, and as a promising application for urea-assisted water electrolysis about 190 mV less was required to provide 10 mA cm⁻² in the two-electrode system, indicating the energy-efficient nature for hydrogen evolution. The study provides some novel insights into the Ni/Co catalyst design and fabrication with efficient catalytic synergism for electrocatalysis.