Ligand-mediated electrocatalytic activity of Cu-imidazolate coordination polymers for OER in water electrolysis

Copper is an Earth-abundant element promising for the synthesis of robust and efficient oxygen evolution reaction (OER) electrocatalysts. In this study, three Cu-imidazolate coordination polymers (Cu-Im, Cu-mIm, and Cu-bIm) are electrochemically synthesized and examined as OER catalysts whose activity can be modulated by the coordinating ligands of imidazole (Im), 2-methylimidazole (mIm), and benzimidazole (bIm). During the water electrolysis, Cu-Im and Cu-mIm are partially oxidized to form CuO particles, a well-known OER catalyst, while Cu-bIm does not. Due to the in situ formation of CuO during the electrolysis and weaker hydrophobicity of Im ligand, Cu-Im shows the highest electrocatalytic activity with a modest overpotential of 500 mV delivering a current density of 10 mA cm−2 and a Tafel slope of 215 mV dec−1 in 1 M KOH. On the contrary, the hydrophobic and anti-corrosion property of the bIm ligand stabilizes the Cu-bIm during the electrolysis without CuO formation. The hydrophobicity of the coordinating ligand influenced the electrocatalytic activity, resulting in the order of Cu-Im > Cu-mIm > Cu-bIm. Post-reaction analyses of the Cu-imidazolate coordination polymers reveal variations in the oxidation state of Cu, which has not been explored in previous studies. This work underlines that the ligand properties can regulate the catalytic activity of metal-ligand coordination polymer.