Ultra-small β-Ni(OH)2 quantum dot catalyst with abundant edges for an efficient urea oxidation reaction†

Abstract

The development of efficient nonprecious-metal catalysts for the urea oxidation reaction (UOR) to improve the efficiency of electrocatalytic water splitting for hydrogen production remains a challenge. Herein, we synthesized ultra-small β-Ni(OH)₂ quantum dot (US-β-Ni(OH)₂ QD) catalysts with abundant edges via a coupled co-precipitation and anion-exchange approach. The obtained US-β-Ni(OH)₂ QD catalyst exhibits high activity toward the UOR and required a potential of only 1.48 V (vs. RHE) to reach 151 mA cm⁻². Notably, the US-β-Ni(OH)₂ QD catalyst exhibits 4.1 and 96 times higher current density than do β-Ni(OH)₂ nanosheets (38.34 mA cm⁻²) and a Pt mesh electrode (1.57 mA cm⁻²), respectively, at a potential of 1.48 V (vs. RHE). The UOR catalytic reaction mechanism reveals that the US-β-Ni(OH)₂ QD catalyst features a high density of edge sites, where the oxygen vacancy concentration far exceeds that of the basal plane. This unique oxygen-vacancy-rich edge structure endows the US-β-Ni(OH)₂ QDs with a low energy barrier (0.96 eV) for the self-oxidation of Ni(OH)₂ to NiOOH, thereby facilitating the rate-determining step of the entire urea degradation process. This work provides a new approach for synthesizing ultra-small hydroxide quantum dot catalysts with efficient UOR activity at low cost.