Study On Catalyst Of Highly Selective Ethanol Oxidation For Electrochemical Hydrogen And Chemical Cogeneration

In recent years,with the gradual depletion of fossil fuels and the increasingly acute Environmentalal problems such as the greenhouse effect,more and more researchers focus on the development of new energy.Among the green energy to replace fossil fuels,hydrogen energy is favored because of its wide range of raw materials,high calorific value and clean products.In order to realize the large-scale utilization of hydrogen energy,efficient and low-cost hydrogen production process has become a key issue in the development of hydrogen energy.Among the existing hydrogen production methods,electrochemical hydrolysing hydrogen production has the characteristics of Environmentalal protection and safety,low price and stable industry,which is an important way to produce hydrogen.However,the problems of high anode potential and low market value of oxygen result in high cost of hydrogen production and limit its large-scale production and application.It is expected that the anodic oxygen precipitation reaction of electrolysis water hydrogen production can be replaced by the selective oxidation reaction of biomass.In order to solve these problems,some researchers propose the use of organic matter as the anode substitute substrate to realize electrochemical hydrogen and chemical cogeneration under low potential.Among all anode substrates,ethanol,as the most common organic biomass,has the advantages of extensive material sources.At the same time,the equilibrium reaction potential required for electrochemical ethanol selective oxidation is low,and acetic acid,the main oxidation product,has a broad market,which can support large-scale industrial hydrogen production.However,at present,selective ethanol electrooxidation catalyst still can not meet the requirements,the poor activity,selectivity,and poor stability and other problems of catalysts restrict the promotion and development of this application.In this paper,highly selective ethanol electrooxidation catalysts for electrochemical hydrogen and chemical cogeneration were studied.The process of electrochemical ethanol selective oxidation and the key factors of catalyst design were studied by synthesis optimization,electrochemical testing and electrochemical In situ characterization.By optimizing the morphology and composition of nanomaterials,a series catalysts with high activity,high selectivity,high stability and high selectivity were prepared.The relationship between the structure and properties was investigated by electrochemical In situ characterization.The device of electrochemical hydrogen and ethanol oxidation cogeneration was constructed to achieve the ultimate goal of cogeneration of acetic acid and hydrogen under low voltage.At the same time,the active sites and reaction paths were systematically studied to clarify the composition and internal structural causes of activity and stability,and establish the relationship between morphology,composition and performance,providing reference for the subsequent design and synthesis of related catalysts.The main results are as follows:（1）The activity of Pd-based catalyst was improved by alloying.P-doped amorphous Pd P_0.1 nanoparticles(a-Pd P_0.1)were synthesized by solvent reduction method,and had higher catalytic activity than crystal Pd nanoparticles of ethanol electrooxidation.At 0.75 V（vs.RHE,the same below）,the mass activity and specific activity of a-Pd P_0.1 reached 4851m A·mg^-1_Metaland 8.57m A·cm^-2,respectively,which were 4.06 and 2.6 times that of Pd with good crystallinity.There is no long-range ordered structure in a-Pd P_0.1,and there are many low coordination active sites on the surface.Meanwhile,the doping of P causes electron Pd deficiency center,which enhances the adsorption capacity of catalyst with reactants and improves the activity of ethanol oxidation.（2）The synthesis of Au alloy catalyst improves the activity and stability of ethanol selective electrooxidation.Au Cu_1.29 alloy catalyst was synthesized by liquid phase synthesis method and which improved overall activity and selectivity of the Au-based catalyst.The catalyst oxidized ethanol to acetic acid（salt）in alkaline electrolyte with high selectivity（>97%）and high stability.The results of isotope substitution experiment and in situ electrochemical infrared test showed that the alloying of Au-based catalyst accelerated the water activation on the surface,promoted the formation of intermediate Au-（OH）_ad,and improved the activity.Au Cu_1.29 was used as the anode catalyst to construct the flow cell.Under the voltage of less than 1.2 V,the flow cell worked for more than 240 min.The synthesis of hydrogen and acetic acid（salt）with high selectivity（>95%）was realized at the anode and cathode.（3）Synthesis of nickel-based selective ethanol electrooxidation catalytic material to reduce the catalyst cost.Non-noble metal Ni₃S₂ nanowires（Ni₃S₂NWs）with abundant defect structure was synthesized by solvothermal method.The catalyst showed high activity in the electrooxidation reaction of ethanol.Ni₃S₂ NWs is formed by small nanoparticles through directional attachment mechanism and has a large number of defects.Ni₃S₂ NWs catalyzed ethanol electrooxidation has low initial potential（1.31 V）and high activity(mass activity is 8716 m A·mg^-1_metal at 1.5 V),and the selectivity of acetic acid（salt）product is up to 99%.It has been showed that the combination of S and abundant defect structures on the surface makes the Ni（II）more easily oxidized into Ni OOH intermediate species with high activity,thus improving the performance of Ni₃S₂ NWs.（4）The structure-activity relationship of anions on the catalytic activity of selective ethanol electrooxidation of Ni-based materials was further investigated.The results showed that Ni-based materials had a selectivity of>95%for acetic acid,but the activity varied with the type and quantity of anions.For the Ni-chalcogenides with different anions,the activity increased gradually according to the order of Ni O,Ni S and Ni Se,indicating that the large anions are conducive to improving the activity of ethanol oxidation.The sequence of Ni₃Se₂,Ni Se and Ni Se₂ activity of Ni-Se compounds with different Ni/Se ratios was further studied.It was found that the higher the proportion of anions,the better the activity was.At 1.5 V,the specific activity of Ni Se₂ was 70.2 m A·cm^-2,which showed the best catalytic performance of ethanol oxidation.The analysis shows that anionic ions regulate the Ni-Ni layer spacing in the nickel-based catalyst,and the large layer spacing makes it easier to transform into the active phase（Ni OOH）,which improves the catalytic activity of selective ethanol electrooxidation.