High Efficiency Hydrogen Production From Polyols And Glucose Electrolysis Using Polyoxometalate As A Liquid-catalyst

Hydrogen is an important renewable clean energy source.Compared with water electrolysis for hydrogen production,the energy consumption for the production of hydrogen from electrolyzed alcohols is significantly reduced,which has a good development prospect.However,noble metal catalysts used in the electrolysis process are very sensitive to some of the impurities in the fuels and are prone to poisoning.Furthermore,C-C bond cannot be effectively oxidized at low temperature.Polyoxometalates?POMs?are water-soluble molecular metal-oxide clusters that are resistant to most organic and inorganic contaminants.POMs is used as a catalyst and charge carrier during the electrolysis process and alcohols can be directly oxidized to produce hydrogen at a lower temperature.In this research,aqueous polyoxometalates?POM?is used as a liquid catalyst,and hydrogen is produced from polyols.Polyols are oxidized by POM by heating at first,and the electrons are transferred to POM molecules,the oxidized POM converts to the reduced POM.During the electrolysis process,the reduced POM loses electrons and converts to the oxidized POM at the anode.Protons from polyols diffuse to the cathode and are reduced to hydrogen.Firstly,glucose was selected as a fuel and PMo₁₂2 was selected as a liquid catalyst to investigate the influence of heating temperature,heating time and pH of solution on the heat-induced reaction during the pretreatment process.The results showed that the reduction degree of the PMo₁₂2 catalyst and hydrogen production performance were significantly increased by increasing the pretreatment time and the pretreatment temperature,adjusting the pH of the glucose-PMo₁₂2 solution before and after pretreatment.The suitable reaction conditions are:the pretreatment temperature is100?,the pretreatment time is 4 h,and the pH value of the solution is adjusted before and after the pretreatment.Glucose was used as a fuel to electrolyze the glucose-PMo₁₂2 solution at current densities of 0.2,0.25,and 0.3 A/cm².The results showed that the voltage was stable during the electrolysis process.Theoretically,the electric energy consumption is only1.755 kW·h/m³ at 0.2 A/cm²,which is only 42.48%of the energy consumed by the water electrolysis.To investigate the effect of hydroxyl groups in the polyols on hydrogen production,alcohols such as methanol,ethylene glycol,glycerol,erythritol,xylitol and sorbitol were selected as fuels.It was shown that the more number of hydroxyl groups,the higher the reduction degree of alcohols was,and the lower onset for electrolysis was needed.At a higher current density under the same voltage,less energy was consumed by electrolysis.The results of UV-vis and¹H NMR showed that there was a pre-association between hydroxyl group and PMo₁₂,which was weak in small alcohols,and the interaction was stronger with more hydroxyl groups.¹H NMR,¹³C NMR and FTIR showed that the products of the anode solution after electrolysis contained hydroxyl,ether bond and aldehyde group.After several cycles of electrolysis,it was found that reaction between PMo₁₂2 and glycerol form intermediate products.As a liquid catalyst,PMo₁₂2 can not only be used repeatedly in the electrolysis process,but also improve the hydrogen production efficiency of glycerol.