Utilization of a dicopper(II) complex of tetrapyridyl ligand as the precursor for the synthesis of copper-based composites and their catalysis

Herein reported are the catalytic properties of the composites derived from complex [Cu2(tpbn)(CH3OH)4(ClO4)2](ClO4)2 (1) of tetrapyridyl ligand N,N,N′,N′-tetrakis(2-pyridyl-methyl)-1,4-butanediamine (tpbn). Complex 1 was a precursor of the composites catalytically active for water oxidation and CO2 reduction reactions. Under the anodic potential of +1.20 V vs. Ag/AgCl, composites deposited on tin-doped indium oxide (ITO) electrodes from the solutions of complex 1 at pH 9.0–13.5 are highly active for water oxidation reaction (WOR). In contrast, under the cathodic potential of −1.20 V vs. Ag/AgCl, the species deposited on the copper surface from the solutions of complex 1 at pH 6.7 can efficiently catalyze CO2 reduction to CO. Scanning electron microscopy (SEM) showed that the composites on ITO and Cu surfaces were particulate materials. X-ray photoelectron spectroscopy (XPS) and x-ray-excited Auger electron spectroscopy (XAES) analysis revealed that the composites mainly contain cuprous oxide (Cu2O) and copper oxide (CuO) in different ratios, which showed different catalytic activity to water oxidation and CO2 reduction reactions in copper-free aqueous solutions under low overpotentials. This work demonstrated that metal complexes are good candidates for preparing robust, noble-metal-free catalysts for reactions relevant to renewable energy sources.