Pure Hydrogen Production from Polyol Electrolysis Using Polyoxometalates as Both a Liquid Catalyst and a Charge Carrier

A novel process of producing pure hydrogen from polyol electrolysis is presented in this study. First, polyols are oxidized by polyoxometalates (POMs) at elevated temperatures; the oxidized POMs then convert to reduced POMs after receiving electrons. The reduced POMs then lose electrons and convert to oxidized POMs at the anode in the electrolysis process. Protons from the polyols diffuse to the cathode and are reduced to H2. In this process, POMs is utilized as both a catalyst and a charge carrier. The electric energy consumption is 1.755 kWh per normal cubic meter of H2 (Nm–3H2) at 0.2 A cm–2, which is approximately 42.5% of the energy consumed during water electrolysis. It is shown that the number and structure of hydroxyl groups influence hydrogen production significantly. The degree of reduction of POMs improves as the number of hydroxyl groups in fuel molecules increases. The higher degree of reduction of the POMs catalyst speeds up the reaction between POMs and the polyols. Preassociation between POMs and polyols was characterized by UV–vis and 1H NMR spectroscopies.