Research On Hydrogen Production By Modified Anode Reaction Assisted Cathode Electrolysis

With the progress and development of society,non-renewable resources such as coal,natural gas and oil are increasingly exhausted,while human’s demand for fossil fuels is constantly increasing.Global energy demand is expected to increase from 18 terawatts in 2013 to 24 terawatts in 2040,according to projections.Therefore,excessive use of fossil fuels will increase greenhouse gas emissions and eventually lead to serious environmental pollution.In this regard,advanced technologies to produce clean energy are the solution to achieving sustainable development of human society.Efficient technologies for clean energy production improve energy efficiency and can solve environmental problems.Hydrogen(H2)is considered to be the most promising energy carrier as an alternative to fossil fuels due to its environmental protection,zero carbon emissions and high energy density.Hydrogen can be produced using a variety of methods.Some methods,such as producing h ydrogen from fossil fuels,release toxic gases into the environm ent,and the hydrogen produced is not entirely pure.Electrochemical water decomposition is considered to be one of the cleanest methods of hydrogen production.Therefore,two new anodic reactions were designed to replace the traditional oxygen evolution reaction(OER),and two self-supporting electrocatalysts were designed to achieve a large amount of energy saving electrolysis of aquatic hydrogen.(1)Traditional OER was replaced by urea oxidation reaction(UOR),and energy saving was achieved by modified anode reaction.The self-supported electrodes FeAl-LDH/NiS and FeAl-LDH/NF were synthesized by microwave method.The morphology and properties of nickel foam(NF)were controlled by modifying the base,and NiS/NF was obtained by vulcanization.FeAl-LDH/NiS showed better UOR reaction with hydrogen evolution(HER)than FeAl-LDH/NF.UOR only needs a potential of 1.39 VRHE to reach a high current density of 350 mA/cm~2,which is much lower than 1.64 VRHE of OER,and the slope of Tafel corresponding to UOR system is only 42 mV/dec,which is much lower than 87 mV/dec of OER system.FeAl-LDH/NiS can also be used as a UOR/HER bifocal catalyst with good hydrogen evolution(HER)performance:At a potential of-0.19 VRHE,FeAl-LDH/NiS can achieve a high current density of 350 mA/cm~2.FeAl LDH/NiS at the same time as the anode and the cathode of UOR‖HER electrolytic cell,the voltage of 1.48 V when the current of 100 mA/cm~2 density,showed significant activity,and OER‖HER cell under the same current density need to voltage of 1.81 V.The 24 h stability of UOR,HER and urea electrolysis is tested.The current density is almost no attenuation,and the stability is good.In conclusion,using UOR instead of OER as the anode reaction and designing FeAl-LDH/NiS bifunctional electrocatalyst,the energy saving of electrolytic water hydrogen production was realized.(2)A new type of anode reaction Cu(Ⅰ)/Cu(Ⅱ)REDOX cycle is used to replace the traditional OER and organic oxidation(UOR,GOR,etc.).At the potential of 0.75 VRHE Cu2O is electrochemical oxidized to Cu(OH)2,and then the glucose in the electrolyte immediately reduces Cu(OH)2 to Cu2O,which completes the Cu2O/Cn(OH)2 cycle,that is,the Cu(Ⅰ)/Cu(Ⅱ)REDOX cycle.The Cu2O/NF electrocatalyst was prepared.By adjusting the concentration,temperature,time and synthesis method,the performance of Cu2O/NF electrocatalyst was regulated.The Cu(Ⅰ)/Cu(Ⅱ)REDOX cycle as the anode reaction,only 0.99 VRHE potential to achieve 100 mA/cm~2 current density,but conventional OER needs 1.98 VRHE potential to achieve the same current density.Cu2O/NF also has good HER properties:it provides a current density of 350 mA/cm~2 at a potential of-0.21 VRHE.It is worth noting that the Cu2O/NF and at the same time as the anode and the cathode assembly Cu(Ⅰ)/Cu(Ⅱ)REDOX cycle coupling HER electrolyzer,at 0.99 V,150 mA/cm~2 current density,and traditional OER‖HER cell may take 2.03 V voltage to achieve the same current density,Thus,substantial energy saving was achieved.Then,the Cu(Ⅰ)/Cu(Ⅱ)REDOX cycle and the 24 h stability of HER were tested.It was found that the CU2O/NF electrocatalyst has good stability.In addition,a variety of substrates including xylose,mannose,alolone and galactose were expanded,which provided a reference for the follow-up work.