Research On Thermochemical Cycle For Hydrogen Production Based On Electrodeposition Of Iron In Molten Salts

The two-step thermochemical cycle for hydrogen production is a rapid and new hydrogen production process.It is clean and sustainable that there is no greenhouse gas emission during the process.Hydrogen and oxygen are produced in two steps,eliminating the need for gas separation at high temperatures.However,subject to thermodynamics,thermochemical cycles are mostly carried out above 1200℃.The extremely high temperature causes the cycle can not be stably carried out for a long time,and the high temperature also brings great technical challenges to the material of the reactor.Reducing the reaction temperature and achieving hydrogen production at low temperatures is one of the most important development directions of thermochemical cycles.In this paper,LiFeO₂/Fe electro-thermochemical cycle system was constructed by using molten salts as electrolytes.The thermodynamic analysis of the cycle was carried out.The hydrogen production efficiency and hydrogen production mechanism were studied by cyclic experiments.The hydrogen production system was improved by Mo doping.The reactants and products were characterized by XRD,SEM and other methods.The hydrogen production performance after doping was studied.Thermodynamic analysis confirmed the feasibility of electro-thermochemical cycle at500℃.On the basis of thermodynamics,it was confirmed by experiments that hydrogen production can be achieved under the molten salt system.It is found that electrothermal chemical hydrogen production has good hydrogen production performance.The addition of Fe₂O₃,electrolysis time and deionized water flow effected on hydrogen production.The cycle experiments showed good stability which four electro-thermochemical cycles were carried out,and the average hydrogen production per cycle was 58 ml.The mechanism of electro-thermochemical cycle for hydrogen production was that Fe₂O₃ first reacted with LiOH to form LiFeO₂,then LiFeO₂ was electroreduced to Fe at the cathode,and O₂ was released at the anode,and Li₂O was formed at the same time.With LiOH and Li₂O,steam and Fe electroreduced reacted back to LiFeO₂ while producing H₂.The improvement of Fe₂O₃ doped Mo was carried out.The results showed that the doping Mo significantly improved the cycle stability of Fe₂O₃,and increased the hydrogen production rate and hydrogen production.Four cycles were carried out,and the average hydrogen production was 83 ml.XRD and SEM characterization and electrochemical studies showed that the addition of Mo reduced the electrochemical reduction polarization of Fe₂O₃and promoted the electroreduction of Fe₂O₃,thereby increasing the hydrogen production rate and hydrogen production.Electrothermal chemical cycle provides a new method for hydrogen production via water splitting thermochemical cycle in lower temperature.