Palladium And Platinum Complex Metal Sulfides For Electrocatalytic Hydrogen Evolution And Oxygen Reduction

The blood of industry is energy,and the use of energy in the world today is mainly fossil energy such as oil and coal,and with the emergence of environmental pollution and energy crisis caused by fossil energy,the development of environmentally friendly and effective new energy has become a worldwide issue,and hydrogen（H₂）and hydrogen peroxide（H₂O₂）can be used as zero-carbon energy for fuel cells.Among the many preparation processes of hydrogen and hydrogen peroxide,electrochemical synthesis has attracted much attention because of its advantages such as no pollutant generation,simple and convenient process,and less restriction of storage and transportation.However,in the process of electrochemical hydrogen synthesis,there are problems such as low efficiency and high energy consumption,and a high activity catalyst is needed to complete the hydrogen evolution reaction efficiently.The traditional preparation process of hydrogen peroxide mainly uses anthraquinone method,but the concentration of hydrogen peroxide synthesized in this process is too high,which has a certain danger and is not convenient for transportation.At present,precious metals are mainly used as catalysts in electrochemical preparation.Due to the price and production of precious metals,there are certain restrictions on their large-scale application,so it is necessary to reduce the use of precious metals in hydrogen peroxide catalysts.Based on this,this thesis optimized the catalysts for hydrogen production by electrolysis of water and electrochemical synthesis of hydrogen peroxide.The specific work contents are as follows:（1）Two-dimensional metal sulfides（TMDs）have always been a research hotspot in the field of electrocatalysts.In this chapter,firstly,the hydrothermal temperature is adjusted to reduce the agglomeration of molybdenum disulfide（MoS₂）,and then palladium（Pd）is deposited on MoS₂ nanosheets.On MoS₂ nanosheets,Pd exists in the form of nanoparticles,and Pd nanoparticles not only modulate the electronic structure of the sulfur atomic layer on the MoS₂ base surface,but also act as a new active center to improve the active area of the material.At the current density of 10 mA cm^-2,the overpotential of Pd/MoS₂ reaches 52 mV（vs.RHE）,and the Tafel slope is 119 mV dec^-1,which has relatively excellent catalytic performance of electrolytic water,which provides more reference ideas for metal-carrier mode catalysts.（2）In this chapter,metal Pd is loaded on zinc indium sulfur（ZIS）,a two-dimensional metal sulfide with a large amount of negative charge on the surface of ZIS,so that Pd can be evenly dispersed,and the formed Pd nanoclusters serve as the main catalytic active center.On the other hand,Pd induces the generation of more sulfur vacancy during the heat treatment process,and the two synergies enhance HER catalytic ability.When the current density is 10 mA cm^-2,the overpotential energy of Pd/ZIS-T sample reaches 24 mV,and the Tafel slope is only 15 mV dec^-1,showing a faster reaction rate,indicating that Pd/ZIS-T catalyst has hydrogen evolution kinetics based on Heyrovsky reaction.The sulfur vacancy introduced on ZIS nanosheets can provide an additional way to generate H_ads,increase the formation rate of H_ads,and can produce a synergistic catalytic effect with Pd nanoparticles.Pd-S site can promote H-OH bond cleavage to form OH^*and H^*.And Pd/ZIS-T can stable output more than 100 h at 10 mA cm^-2.（3）In view of the highly dispersive effect of ZIS on metals as a carrier,a composite catalyst with high selectivity for hydrogen peroxide was prepared by combining a small amount of metal platinum（Pt）with ZIS.Due to the strong adsorption effect of Pt on^*OOH,O₂ can be reduced better.At the same time,the presence of sulfur will inhibit the strong adsorption of Pt on^*OOH,reduce the occurrence of side reactions,and support the reduction reaction of Pt on 2 e^-.Finally,a platinum-based catalyst with high Selectivity for hydrogen peroxide was obtained（Pt₅/ZIS-S,selectivity≥95%）.At 0.1 V,the H₂O₂yield of Pt₅/ZIS-S could reach 527.3 mmol g^-1 h^-1.At the same time,Pt₅/ZIS-S can inhibit the digestion of generated H₂O₂and prevent the decrease of production caused by H₂O₂ accumulation.