Synthesis Of Sulfur-doped Gold-based Platinum Group Aerogels As Catalysts And Study On Their Electrocatalytic Performance

Developing new clean energy technologies(such as proton exchange membrane fuel cell and water splitting,etc.)is one of the way to solve the existing environmental pollution,energy shortage and other problems.However,the slow kinetics of the important electrode reactions involved in these technologies limits the overall reaction rate of the energy technologies.At present,the commercial catalysts are still noble metal electrocatalysts represented by Pt.But the scarce resources,low reserves,high cost and poor anti-poisoning performance are the main disadvantages of Pt-based electrocatalysts.Therefore,developing the noble metal electrocatalysts with low loading and high electrocatalytic performance is still one of the hot research topic.As is known to all,the change of d-electron structure of the noble metal can enhance the electrocatalytic performance of the noble metal electrocatalysts in oxygen reduction reaction(ORR)and hydrogen evolution reaction(HER).The electronic structure of Pt groups noble metal nanomaterials usually varies with their size and morphology,and is closely related to the metal constituents and defects on their surface.The nanowire-like noble metal aerogels have intrinsic advantages of high aspect ratio and high density of active sites.Therefore,in recent years,the research of noble metal aerogels has attracted extensive attention.In addition,the multi-composite noble metal nanomaterials can effectively enhance the electrocatalytic activity by utilizing the synergistic effect,electronic effect and strain effect of each constituent.Moreover,Au element is widely used in Pt groups noble metal electrocatalysts to improve the stability of electrocatalysts due to the good resistance to CO poisoning.On the other hand,the electrocatalytic performance of noble metal electrocatalysts also depends on the composition and proportion of the surface facets.Therefore,the study of structure-efficiency of these noble metal electrocatalysts have important guiding significance for the synthesis of electrocatalysts with excellent performance.Therefore,the synthesis and application in electrocatalysis of Au-based Pt group(Pt,Pd and Ir)noble metal aerogel electrocatalysts are the main research goal in this thesis.A series of Au-based Pt groups aerogel electrocatalysts were synthesized by utilizing the strategies of the structural characteristics of nanowire-like aerogels,the facet regulation,sulfur element doping and alloying effect.Then their ORR and HER electrocatalytic activities and stabilities were investigated.This thesis is divided into five chapters(Chapter 1 is the introduction),and the detailed research content is as follows:In chapter 2,S-doped AuPb nano wire-networks(abbreviated as S-AuPb NWNs)are obtained by NaBH4 reduction of an extended nanowire-network of loose aggregation of 2 nm Au nanoclusters resulting from Pb2+ ion-directed self-assembly via the chelation between-SH and Pb2+ ions.Then,the S-doped AuPbPt(abbreviated as S-AuPbPt)alloy aerogels with proper PtS are synthesized by conformal growth of Pt onto S-AuPb NWNs as templates,which are achieved by regulating the reaction parameters such as the content of Pb and S in the template,the pH value and the concentration of Pt(Ⅳ)ions.Moreover,the results of X-ray Photoelectron Spectroscopy(XPS)characterization and density functional theory(DFT)calculations show the formation of a proper content of PtS in the resulting S-AuPbPt alloy aerogels remarkably downshifts the d-band center of Pt and then improves the resistance of Pt active sites against oxidation,which can further render the Pt surfaces more catalytically active for the ORR and more structurally stable.As expected,the as-prepared S-AuPbPt alloy aerogels with optimal PtS content exhibit excellent electrocatalytic activity towards both the ORR(Eonset=1.047 V and E1/2=0.921 V)and HER(Eonset=-2 mV and η10=12 mV)and better durability in acidic media.In chapter 3,firstly,the content of S species(PbS and PbS2)in the S-doped AuPb(abbreviated as S-AuPb)aerogels template is regulated by the amount of NaBH4.Then,the AuPd-SB67A33 aerogels with optimal ratio of bridging(B)S22-ligands(PdS2)and apical(A)S2ligands(Pd2.8S)are synthesized by conformal growth of Pd onto the surface of S-AuPb aerogels template.The d-band center of Pd in AuPd-SB67A33 aerogels is suitable for ORR,which results from the appropriate ratio of Pd2.8S and PdS2 in the resulting AuPd-SB67A33 aerogels.Moreover,the formation of alloys AuPd,Pd2.sS and PdS2 on their surface can not only achieve high dispersion of Pd active sites,but also improve their anti-oxidation resistance,which in turn can greatly improve their catalytic activity towards the ORR.As is expected,the as-prepared AuPdSB67A33 aerogels indeed exhibit excellent electrocatalytic activity towards the ORR in alkaline media.The Eonset and E1/2 of AuPd-SB67A33 aerogels are 1.067 V and 0.970 V,which are 35 mV and 85 mV higher than those(1.032 V and 0.885 V)of commercial Pt/C catalysts,respectively.In addition,their jk(41.67 mA cm-2),mass activity(2.60 A mgpd-1)and specific activity(2.67 mA cm-2)at 0.9 V(vs.RHE)are 12.5,20 and 12 times higher than those(3.34 mA cm-2,0.13 A mgPt-1 and 0.22 mA cm-2)of commercial Pt/C catalysts.And the as-prepared AuPd-SB67A33 aerogels also exhibit excellent durability.In chapter 4,S-doped AuIr(abbreviated as OR180-Aulr-SB46A54,the OR means Ostwald ripening and 180 means the reaction temperature is set as 180℃)aerogels with excellent HER performance are successfully synthesized by conformal growth of Ir onto S-AuPb aerogels template,which are obtained by the ethylene glycol as solvent and reducing agent and regulating the reaction parameters such as the reaction temperature and the injection rate of Ir(Ⅲ)ions.The as-prepared OR180’-AuIr-SB46A54 aerogels exhibit excellent electrocatalytic activity towards the HER in 0.5 M H2SO4 solution.The η10 of OR180-AuIr-SB46A54 aerogels is only 13 mV,which is 15 mV lower than that of the commercial Pt/C catalysts.The mass activity at-0.05 V(13.8 A mgIr-1)and current density at-0.07 V(320.7 mA cm-2)are 6.9 and 4.5 times higher than those(2.0 A mgPt-1 and 71.8 mA cm-2)of commercial Pt/C catalysts.In addition,the as-prepared OR180-AuIr-SB46A54 aerogels also exhibit better stability.Furthermore,the HER activity of ORT-AuIr-S aerogels prepared at different temperatures(T)is closely related to the ratio of their {100} facets,which may result from that the hydrogen adsorption capacity of different Ir facets is {100}>{110}>{111}.In addition,the adsorption of reactants and desorption of products can be kept in balance with the proper proportion of {100} facet in ORTAuIr-S aerogels,which can further greatly enhance the reaction kinetics towards the HER.Therefore,the as-prepared OR180-AuIr-SB46A54 aerogels with the proper ratio(32.22%)of {100}facet would exhibit excellent HER activity.In Chapter 5,the above works have been summarized and prospected.In summary,in this thesis,three types of Au-based Pt group aerogels(S-AuPbPt alloy aerogels,AuPd-SB67A33 aerogels and OR180-AuIr-SB46A54 aerogels)are successfully synthesized.And their electrocatalytic performance towards the ORR and HER are also investigated,respectively.Finally,the Au-based Pt group aerogels with excellent electrocatalytic activity and stability are selected.