Influence of the pendant groups on electrochemical water oxidation catalyzed by cobalt(ii) triazolylpyridine complexes

Abstract

The development of low-cost catalysts for the water oxidation reaction (WOR) is important for solving the bottleneck issues in water splitting and benefits the widespread utilization of renewable energy sources. Herein, four cobalt(II) triazolylpyridine complexes, namely [Co(DTE)₂(H₂O)₂](ClO₄)₂·CH₃COCH₃ (1), [Co(DTE)₂Cl₂]·2CH₃OH (2) (DTE = (1-(2-acetoxymethyl)-4-(2-pyridyl)1,2,3-triazole), [Co(DTEL)₂(CH₃OH)₂](ClO₄)₂ (3), and [Co(DTEL)₂Cl₂]·H₂O (4) (DTEL = (1-(2-hydroxy)-4-(2-pyridyl)1,2,3-triazole), were synthesized and characterized. The crystal structures of 1–3 were determined by X-ray single crystal diffraction analysis. The electrocatalytic water oxidation by 1–4 was studied in 0.1 M NaOAc–HOAc solutions. Complexes 1–4 were single-site molecular catalysts for the WOR under near-neutral conditions. The overpotentials for the WOR were 440 mV and 480 mV. The faradaic efficiencies were 77–92%. The rate constants k_cat were 0.21–0.96 s⁻¹. The catalytic activities were affected by the pendant groups of DTE and DTEL. Complexes with DTE (1 and 2) showed better activities than those with DTEL (3 and 4). Moreover, complexes 1–4 adsorbed on indium-doped tin oxide (ITO) and glassy carbon electrode surfaces were active for the WOR. A mechanism was proposed for the WOR catalyzed by 1–4.