Boosted urea electrooxidation activity by dynamic steady blending CoOOH–Ni(OH) 2 nanoclusters for H 2 production in a pH-asymmetric electrolyzer

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 12; no. 36; pp. 24126 - 24135
• Main Authors: Peng, Shih-Mao, Chang, Shu-Ting, Chang, Chia-Che, HN, Priyadarshini, Chang, Chun-Chih, Wu, Kuan-Chang, Huang, Yung-Hung, Chen, Yi-Chia, Kuo, Tsung-Rong, Pao, Chih-Wen, Chen, Jeng-Lung, Wang, Di-Yan
• Format: Journal Article
• Language: English
• Published: 18.09.2024
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/D4TA04241G

Electrochemical urea oxidation reaction (UOR) is a promising alternative to the oxygen evolution reaction for reducing the overall potential of the hydrogen evolution reaction during water electrolysis. The theoretical potential for the UOR is only 0.37 V versus reversible hydrogen electrode (RHE). However, the kinetics of the six-electron transfer process involved in the UOR are inherently sluggish, resulting in high overpotential during the reaction. This study designed an active catalyst with a lower kinetic barrier in the UOR by fabricating blending CoOOH–Ni(OH) 2 nanoclusters through the structural transformation of amorphous Co–Ni hydroxide films. This structural transformation was investigated using high-angle annular dark-field scanning transmission electron microscopy, corresponding energy-dispersive X-ray spectroscopy, and in situ X-ray absorption spectra. The blending CoOOH–Ni(OH) 2 nanoclusters exhibited superior electrocatalytic activity in the UOR in an alkaline environment, achieving a low onset potential of 1.24 V ( vs. RHE) in 1 M KOH with 0.5 M urea. We employed the CoOOH–Ni(OH) 2 nanoclusters as anodic electrocatalysts in a two-cell electrolyzer for asymmetric electrocatalysis. Hydrogen could be produced at a remarkable current density of 10 mA cm −2 at a low applied potential of only 0.45 V. Density functional theory calculations revealed that blending CoOOH–Ni(OH) 2 nanoclusters with more oxygen vacancies exhibited a lower Gibbs free energy for the intermediate reaction pathway of NCONH 2 → NCONH, compared with the fine structure of CoNiO x ( x = 2–3). This study lays down a novel pathway for developing new blending electrocatalysts to be used in electrochemical reactions.