Hierarchical NiCr hydroxide nanospheres with tunable domain boundaries for highly efficient urea electro-oxidation

Nickel hydroxide was a promising catalyst for urea oxidation reaction, but its catalytic activity is still far from satisfactory. Structure engineering is an efficient approach to tailoring the electrical conductivity and the quantities of active sites. Herein, a series of hierarchical NiCr hydroxide nanowire-assembled nanospheres with tunable crystallinity have been synthesized by hydrothermal method. The effect of Cr content on the structure and the electrochemical properties of NiCr hydroxides has been investigated. The axially aligned nanowires ensure the exposure of active sites; the crystalline/amorphous domain boundaries are intrinsically more active; the amorphous structure improves the electrical conductivity; the incorporation of Cr³⁺ promotes the charge transfer kinetics. The 10Cr-Ni(OH)₂ with the optimized Cr³⁺ content and domain boundaries shows the best catalytic performance with a reduction of 35 mV in onset potential relative to the α-Ni(OH)₂. In addition, the 10Cr-Ni(OH)₂ demonstrates good long-term working stability.