Research On The Controllable Synthesis And Electrocatalytic Performance Of Novel Transition Metal Alloys, Selenide And Phosphide Nanostructures

Renewable H₂-O₂ fuel cells?RHOFCs?have attracted much attention due to their clean and zero pollution as well as high energy density.Usually,RHOFCs are composed of H₂-O₂ fuel cells?HOFCs?and water electrolysis cells?WECs?two sections.The sluggish kinetics of anodic oxygen evolution reaction?OER?and cathode hydrogen evolution reaction?HER?in WEC section as well cathodic oxygen reduction reaction?ORR?in HOFCs section,are the bottleneck problems for the advancement of RHOFCs.Thus,it is urgent to develop low-cost,high-activity and high stability electrocatalysts for improving the kinetics of those electrode reaction and reducing their overpotentials.Despite great progress that has been achieved on the design of electrocatalysts for RHOFCs,their performance are still needed to be improved for meeting the requirements on commercial applications.In view of the current research status of RHOFCs electrode catalysts,this dissertation will focus on component or phase engineering,microstructure engineering,hybridization and doping multiple modulation strategies,and fabricate a series of Pd-M?M=Cr,Mo,W?alloy nanosheets superstructures,self-supported transition metal chalcogenides(Mo_xW_1-xSe₂)nanowires network,and hollow ternary transition metal phosphides?TMPs?/ultrathin MOOH nanosheets hybrid nanocages via developing wet chemical and precursors topological chemical transformation methods.The electrocatalytic ORR or HER or OER performances of those three typed materials will be systematically examined.Moreover,based on a series of spectroscopic and electrochemical analyses,the origins of the excellent catalytic properties for those catalysts will be suggested yet.At present,some primary results have been achieved,and the details are as follows:?1?A series of ultrathin and highly wrinkled Pd-M?M=Cr,Mo,W?alloy nanosheets flower-like superstructures?NSFSs?have been successfully prepared via one-pot hydrothermal strategy by using polyethenoxy ether as the structure-directing and binder reagents,and Pd?acac?₂ and M?CO?₆ as the metal precursors.The obtained Pd-M NSFSs possess porous structure and the edges or surface active sites of their nanosheets building blocks can be fully exposed.Moreover,there are co-existence of single-atom-like and cluster-like M species on the surfaces of their nanosheets building units,facilitating to mediate the surface or interfacial electronic structure of Pd.The lattice strain that induced by the incorporation of M elements provide the driving force for in-situ assembly of formed Pd-M nanosheets to generate the desired flower-like superstructures.And the polyether plays the key role for controlling the thickness and orientation of nanosheets building units.Electrochemical tests in alkaline solution demonstrate that all the Pd-M alloy NSFSs show greatly enhanced ORR activity relative to pure Pd NSFSs.Among them,the Pd-W NSFSs manifest the highest ORR activity with the half-wave potential of 0.89 V?vs.RHE?,Tafel slop of60 m V dec-1,and the mass specific activity at 0.90 V?vs.RHE?of 0.45 A mg_pd^-1,superior to Pd-Cr and Pd-Mo NSFSs,commercial Pt/C and some recently reported Pd-based or Pt-based catalysts(e.g.Pd₃Pb/Pd nanosheets,Pt@Ni NSMOF,Pd Cu Ni,Pt₂Cu W_0.25/C,etc.).Moreover,the Pd-W NSFSs possess better electrocatalytic stability and anti-CO poisoning capability than Pt/C catalyst yet.As revealed by a series of spectra and electrochemical analyses,the excellent catalytic performance f Pd-W NSFSs originates from their unique microstructure,proper alloy composition and stronger interatomic polarization,which can offer more available electrochemical active sites and efficient modulate the surface/interface electronic structure of Pd that can optimize or balance the adsption/desoption of oxygenated species.This work demonstrate that design and synthesis of 3D porous superstructures can boost the electrocatlaytic ORR performance of Pd-M alloy nanosheets,which may promote their applications in fuel cells or other clean energy fields.?2?A series of self-supported Mo_xW_1-xSe₂ nanowires with high aspect ratios have been prepared by gas-phase selenization treatment of pre-synthesized Mo_xW_17-xO₄₇nanowires precursors that directly grown on carbon cloth substrate via a one-pot hydrothermal route.Due to the too long of the obtained Mo_xW_1-xSe₂ nanowires,they are self-woven to form the network-like motifs on carbon cloth that driven by the van Waals force,which is beneficial to mass transport or electrolyte diffusion.In addition,due to the directly growth of Mo_xW_1-xSe₂ nanowires on carbon cloth,it can reduce the contact resistance and improve the electrical conductivity or interfacial electron transfer kinetic of Mo_xW_1-xSe₂ nanowires.Electrochemical tests demonstrate that all the Mo_xW_1-xSe₂ nanowires networks can efficiently catalyze HER in 0.5 M H₂SO₄media.Among them,the Mo_0.8W_0.2Se₂ nanowires network show the highest HER activity with the Tafel slope of 68 m V dec^-1 and the overpotential to reach 10 m A cm^-2current density of 109 m V,outperforming other component ratio Mo_xW_1-xSe₂and pure WSe₂ nanowires networks as well as recently reported metal chalcogenides based HER catalysts.Moreover,the Mo_0.8W_0.2Se₂ nanowires network can continuously work for 8000 cycles?48h?without loss of their catalytic activity,implying that it possesses exceptional durability or catalytic stability yet.As disclosed by spectroscopic and electrochemical analyses,the excellent catalytic performance of Mo_0.8W_0.2Se₂ nanowires network result from their proper Mo/W molar ration and unique 1D nanowire network structure,which not only can efficiently modulate the surface/interface electronic structure and expose more available edge Mo or W active sites but also can improve the interfacial electron transfer kinetics,facilitating to optimize the adsorption/desorption of H⁺or H₂ species.This work demonstrates that combination of component and microstructure engineering can enhance the electrocatalytic HER performance of metal chalcogenides nanostructures,and promote their application in electrocatalytic water splitting fields.?3?A series of novel hollow Fe_0.3-xCo_0.7-yP/Fe_xCo_yOOH hybrid nanocages?HNCs?have been fabricated through the multiple chemical transformation of pre-synthesized Prussian blue analogues?Fe Co-PBAs?nanocubes,i.e.,firstly oxidation of Fe Co-PBAs in air to form hollow oxide nanocages,then gas-phase phosphorization treatment of hollow oxide nanocages to generate ternary TMPs nanocages,and finally etching the TMPs nanocages in alkaline/ethylene glycol solution to in-situ grow a thin layer of ultrathin amorphous oxyhydroxyl nanosheets.Electrocatalytic tests demonstrate that all the obtained Fe_0.3-xCo_0.7-yP/Fe_xCo_yOOH HNCs can efficiently catalyze OER in alkaline media.Among them,the Fe_0.3Co_0.7P_0.64/OOH_0.36HNCs manifest the best OER activity with the onset oxidation potential of 1.43V?vs.RHE?,Tafel slope as low as 40 m V dec^-1,and the overpotential to approach 10 m A/cm^-2current density of 256 m V,outperforming pure hollow Fe_0.3Co_0.7P nanocages,commercial Ir O₂ and other reported non-precious-metal based OER catalysts.Moreover,the Fe_0.3Co_0.7P_0.64/OOH_0.36HNCs can continuously operate for 3000 cycles?18h?without loss of their initial activity,suggesting that they possess excellent durability or catalytic stability yet.Deduced from a series of spectroscopic and electrochemical analyses,the excellent catalytic performance of Fe_0.3Co_0.7P_0.64/OOH_0.36HNCs originates from their unique hollow structure?facilitate to mass transport and improve material utilization efficiency?,the skillful component combination and the occurrence of heterostructure interface as well as the efficient electronic coupling between their constituents,which can offer more available electrochemical active sites and efficiently modulate the surface/interface electronic structures that may optimize or balance the adsorption/desorption of oxygenated species.This work may shed some light on optimal design of TMPs nanostructures based OER catalysts,and promote their applications in electrocatalytic water splitting or other clean energy fields.