Polyoxometalate based hybrid compound as a pre-catalyst for electrocatalytic water reduction at neutral pH

Abstract

Polyoxometalate (POM) supported metal complex has proved to be a suitable catalyst for water reduction/oxidation in recent studies. To catalyze hydrogen evolution reaction (HER), we have employed a POM-based inorganic-organic hybrid compound [CuII(2,2′-bpy)(H2O)2Cl][CuII(2,2′-bpy)(H2O)2Al(OH)6Mo6O18]·4H2O (1) with a spiral-chain-like structure consisting of Anderson type polyoxometalate, [Al(OH)6Mo6O18]3− onto which Cu-complex, [Cu(H2O)2(bpy)]2+ fragments are supported. This compound acts as a pre-catalyst towards forming the active catalyst for catalyzing hydrogen evolution reaction (HER) by water reduction in a neutral medium. The active catalyst derived from this compound 1 achieves a current density of 1 mA/cm2 at an overpotential of 348 mV. The turnover frequency calculated for the active catalyst is found to be 1.780 [mol H2 (mol Cu)−1s−1] with the Faradaic efficiency of 85%. Graphic abstract: A unique electrochemical structural rearrangement under the electrochemical condition observed for a chain-like structured Cu-complex supported on Anderson type polyoxometalate, [CuII(2,2′-bpy)(H2O)2Cl][CuII(2,2′-bpy)(H2O)2Al(OH)6Mo6O18]·4H2O (1) resulting in the formation of the active catalyst for the electrochemical HER activity. The active catalyst achieves the current density of 1 mA/cm2 with an overpotential of 348 mV with faradic efficiency of 85% at neutral pH.[Figure not available: see fulltext.]