Preparation Of Aluminum-based Amorphous/Nanocrystalline Alloy As An Efficient Water Splitting Catalyst For Hydrogen Evolution

Hydrogen has been considered as an ideal energy carrier for achieving a sustainable clean energy economy by many scientists.Currently,the main method for producing hydrogen is the industrial steam method,however,its energy conversion efficiency is low and a large amount of carbon-containing residues are generated.Electrolyzed water is one of the most promising methods to solve the appeal problem,and the development of high-performance hydrogen evolution catalyst is the key to promote its industrial application.Powder is currently the most common catalyst,which needs to be dispersed in a solvent and then fixed on a glassy carbon electrode by a polymer binder.However,lower load and lower conductivity limit their commercialization.Therefore,in recent years,a large number of researchers have solved these problems by developing three-dimensional self-supporting electrode catalysts.At the same time,due to the limitations of traditional chemical synthesis methods,synthetic materials are mostly low-component alloys,which neglects the synergy between the elements and greatly limits the development of new catalysts.Based on the above two points,this thesis first develops an aluminum-based amorphous alloy catalyst that can serve as a three-dimensional self-supporting electrode and contains a variety of elements,and then further improves the hydrogen evolution activity of the catalyst and further the related mechanism was studied.In the third part of this paper,the amorphous alloy Al₈₀Ni₆Co₃Mn₃Y₅Au₃ was used as the precursor to conduct simple electrochemical dealloying,and a high-performance nano-porous hydrogen evolution catalyst was obtained.In order to study the catalytic activity of hydrogen evolution,linear sweep voltammetry（LSV）,cyclic voltammetry（CV）and Electrochemical Impedance Spectroscopy（EIS）were used.In order to analyze the microstructure of the material,XRD,DSC,SEM,DSC and other test instruments were used.According to the microscopic analysis,after about two hours of electrochemical de-alloying,only a nano-porous structure layer with a thickness of about 200 nm was formed on the surface of the material,while the substrate was still a very perfect amorphous alloy.Therefore,as a self-supporting material,the catalyst had a mechanical strength comparable to that of the raw material,up to 200 MPa.After a constant current test of up to 20 h,a nanofilaments layer only about 500 nm thick appeared between the nano-porous layer and the amorphous matrix.Generally,the strip thickness is between 20 um and 30 um,so from the perspective of corrosion thickness,the service life of the catalyst is estimated to be at least 800 h.The de-alloying Al₈₀Ni₆Co₃Mn₃Y₅Au₃ catalyst has outstanding catalytic activity in acidic solution.Under the current density of 10 mA cm^-2,its overpotential is about 70 mV,and its Tafel slope value is about 39 mV dec^-1,comparable to the commercial precious metal Pt/C electrode(33 mV@10 mA cm^-2,38 mV dec^-1).This high catalytic activity is due to the synergistic effect of the homogeneous dispersion of atoms on the surface of the nanopore.Its excellent catalytic activity is maintained or even better in the long-term reaction,which is due to the multi-component composition of the alloy,and the slow dissolution of the remaining Al makes the electrode have a certain self-optimization effect.At the same time,the aluminum-based amorphous alloy belt itself has high yield strength,high elasticity and good conductivity,so it is an ideal and promising independent catalytic electrode.The fourth part of this paper mainly explores the further enhancement of the hydrogen evolution activity of the material.Compared with crystal,amorphous phase has a larger proportion of random orientation bonds with unsaturated electron configuration.This helps to adsorb the reactants.In addition,the composition of amorphous catalysts is more flexible and can be adjusted over a larger range than that of crystalline catalysts.However,the catalytic activity of pure amorphous alloys is lower than that of crystalline alloys.This is because the conductivity of the amorphous phase is already very low.Therefore,a promising catalyst performance improvement idea should be to combine the advantages of amorphous phase and crystalline state to obtain the best materials.Therefore,this part adopts two methods to prepare amorphous crystal composite phase catalyst:（1）select different temperatures for short time annealing by DSC,and generate nanocrystals in the material;（2）adjust the speed of the copper roller to make it in the completely amorphous and complete crystal speed.The composite phase Al₈₂Ni₆Co₃Mn₃Y₃Au₃catalyst showed excellent catalytic activity in acidic solution.The composite phase Al₈₂Ni₆Co₃Mn₃Y₃Au₃ catalyst showed excellent catalytic activity in acidic solution.Under the current density of 10 mA cm^-2,its overpotential was about 31 mV,and its Tafel slope value was about 28 mV dec^-1,even better than the commercial precious metal Pt/C electrode(33 mV@10 mA cm^-2,38mV dec^-1).The reason for this high catalytic activity is that in addition to the synergistic effect of the uniform dispersion of multi-element atoms on the surface of the nanopore,the nanocrystals near the nano-porous tissue provide a large number of active sites,while the crystals in the composite phase increase the conductivity of the material.In summary,this paper employs AlNiCoMnYAu amorphous alloy strip as the precursor and simply conducts electrochemical dealloying to obtain a high-performance hydrogen evolution catalyst.After that,the catalytic activity of hydrogen evolution was further improved by changing the microstructure of the material.Simple operation methods,widely sourced raw materials and high performance catalysts make it possible to commercialize catalysts.In addition,the way of multi-element development of new materials in this paper provides more options for the future development and exploration of excellent materials,which will also help promote the development of the electrolytic water and hydrogen industry.