Ultra-small β-Ni(OH)2 Quantum Dots Catalyst with Abundant Edges for Efficient Urea Oxidation Reaction

Abstract

The development of efficient nonprecious-metal catalysts for urea oxidation reaction (UOR) to improve the efficiency of electrocatalytic water splitting for hydrogen production remains a challenge. Herein, we synthesized an ultra-small β-Ni(OH)2 quantum dots catalyst with abundant edges (US-β-Ni(OH)2 QDs) by a coupling approach of co-precipitation and anionic exchange. The obtained US-β-Ni(OH)2 QDs catalyst exhibits high activity toward UOR, and the required potential is only 1.48 V (vs. RHE) to arrive at 151 mA·cm-2. Notably, the US-β-Ni(OH)2 QDs catalyst reflects 4.1 and 96 times higher current density than the β-Ni(OH)2 nanosheets (38.34 mA cm–2) and Pt mesh electrode (1.57 mA cm–2) at the potential of 1.48 V (vs. RHE). The catalytic reaction mechanism indicates that the US-β-Ni(OH)2 QDs catalyst with the ultra-small size (~3 nm) has more abundant edges compared to the β-Ni(OH)2 nanosheets, which provides abundant active sites for catalytic reactions. Moreover, it was found that the Ni-OH bonding of the edge in US-β-Ni(OH)2 QDs is more active than the edge and basic plane of β-Ni(OH)2 nanosheets, which promotes the conversion from Ni2+ to Ni3+ and the adsorption of urea molecules, reducing the energy barrier of UOR reaction and thus improving the UOR performance. This work provides a new approach for synthesizing ultra-small hydroxide quantum dots catalysts with efficient UOR activity but low cost.