Construction And Performance Research Of Activity Hydrogen Evolution Catalyst

Hydrogen is an ideal clean energy.The use of renewable energy to prepare hydrogen energy is the premise.As an important method of renewable energy conversion,hydrogen production by water electrolysis is also highly concerned.The actual working voltage is much higher than the theoretical electrolysis voltage for hydrogen evolution reaction?HER?.Thus the energy loss is huge.The electrode material is a key of water electrolysis,it has an important influence on the reaction mechanism of the electrode,reaction rate and electrolytic cell maintenance costs,which plays a very important role for improving the energy conversion efficiency and reducing energy consumption.In this thesis,we have mainly followed the progress and achievements of the research on electrocatalysts for HER,and clearly understand the basic knowledge,challenges and opportunities in this field.In acidic media?proton exchange membrane electrolyzer?,it have strict requirements on the catalytic activity and the long-term stability for HER,which is restricted large-scale production for dependence on precious metals.Catalytic study focus on the composite catalysts of transition metal in the past years.In acidic medium,the activity catalyst is structed for HER: firstly,we should choice an inherent active materials for HER,confirm the active site of materials;then optimize component proportion,build a stable structure and expose the active site;finally,improve conductivity and gas diffusion channel by controlling the morphology,which is also very important and effective to enhance the activity for HER.However,the efficiency of HER is lower in alkaline solution than in acid solutions,owing to the charge transfer induced conversion of water?in alkaline solutions?instead of hydronium ions?in acid solutions?to molecular hydrogen.Thus,improving the water dissociation and accelerating formation of the intermediates adsorption hydrogen atom?Hads?is the key to enhance efficiency of HER in the alkaline solutions.In this thesis,we have carried out the following researches:1)A great deal of evidence has shown that MoS2 is a suitable candidate for the HER in acidic medium.As an efficient HER catalyst,two major challenges should be solved: exfoliating stacked Mo S2 layers to increase the density of the active sites and improving the electrical contacts to active sites.Theoretical calculations and experimental studies have revealed that the HER active sites are located at the edges rather than on the basal surfaces of a MoS2 sheet.However,the edges of the ultrathin Mo S2 are undercoordinated and thermo-dynamically unstable,which is easy to curl up into inorganic fullerene structures.Additionally,the low conductivity of MoS2 catalyst limits electron transport in the catalyst and leads to poor catalytic performance.Recently,the edges of nanostructure 2H-Mo S2 have been observed to be more conductive,suggesting that electron may be passed along the edge from the support substrate to the active edges.Such observation implies that Mo S2 nanosheets perpendicular to the conductive surface would be advantageous to design an efficient HER catalyst.Herein,we synthesized the ultrathin Mo S2 nanosheets perpendicular to reduced graphene oxides?Mo S2?rGO?by a hydrothermal method as an efficient HER catalyst.Therefore,we have shown that the oxygen functional groups of graphene play an anchoring role in fixing Mo S2 nanosheets perpendicular to graphene.The characterization results show that ultrathin Mo S2 nanosheets are uniformly and perpendicularly grown on r GO,and the formation of carbon-sulfur bond is the fundamental reason for the existence of this kind of special morphology.As expected,electrochemical evaluations show that the MoS2?rGO catalyst exhibits excellent electronic conductivity,high density of active edges,high HER electrocatalytic activity and good stability in acidic electrolytes.2)Hydrogen has been vigorously pursued as a promising energy carrier in numerous energy systems.An effective way of producing high-purity hydrogen is to electrochemically split water.However,the efficiency of hydrogen evolution reaction?HER?is lower in alkaline solution than in acid solutions,owing to the charge transfer induced conversion of water?in alkaline solutions?instead of hydronium ions?in acid solutions?to molecular hydrogen.Thus,improving the water dissociation and accelerating the formation of intermediates adsorption hydrogen atom?Hads?is the key to enhance efficiency of HER in the alkaline solutions.The synergistic performance of the catalyst is affected by the composition,morphology and the properties of the heterogeneous interface.In order to fully integrate the advantages of multiple components and alleviate the shortage of a single component,the interface of different components may be different interface electronic state from the single component.Therefore,the interface engineering is vital to rational design and synthesis of the heterogeneous catalyst for high-performance electrochemically applications.A trace Pd modified partially reduced Ni?OH?₂ catalyst has been designed and synthesized on graphene substrate.By adjusting the Ni?OH?₂-Pd-r GO interface,the catalysts show good dispersion,exposing more active sites,effective charge transport path and excellent electrical conductivity,enhanced the catalytic performance of hydrogen evolution.Density functional theory?DFT?calculations show that the strong interaction between the interface atoms,resulting in the formation of a stable Ni?OH?₂@Ni/Pd/rGO morphology,and promote the redistribution of the interface charge.This interface structure is beneficial for the synergistic effect of the catalyst.as an electrocatalyst for the hydrogen evolution reaction,the Ni@Ni?OH?₂/Pd/rGO catalyst shows excellent catalytic activity and stability in alkaline medium.