Precise Control Of Electronic And Geometric Structure Of Palladium-based Nanomaterials And Electrooxidation Of Biomass Alcohol

Liquid fuel cell is a very attractive renewable energy conversion device,which can directly convert the chemical energy stored in the fuel into electrical energy,and has great potential to alleviate the energy crisis and environmental problems.Biomass alcohols（ethanol,glycerol,etc.）are common fuels for liquid fuel cells because of their wide range of sources,low price,low toxicity and high energy density.Palladium（Pd）based catalysts are widely used in alkaline liquid fuel cells because of their excellent electrocatalytic performance.According to the molecular orbital theory,the d orbitals of Pd are fully full,which will lead to the weakening of the binding ability of Pd to the reaction intermediate,resulting in poor C-C bond breaking ability.Because C–C bond has poor breaking ability,it cannot release the energy bound by C-C bond,which will seriously affect the energy conversion efficiency of fuel cells.Therefore,the main content of this thesis is to regulate the electronic and geometric structure of Pdbased nanomaterials by different methods,and investigate their effects on the catalytic performance of biomass alcohols and the cleavage ability of C-C bond.（1）The d-orbital of Pd in the active center of the catalyst is edited by microdepositing rhodium（Rh）and gold（Au）atoms on PdCunanosheets（NSs）,and finally prepare Rh Au-PdCuporous nanosheets（PNSs）.The d orbitals of Pd in Rh Au-PdCuPNSs are edited to form a state with fewer eg electrons and more unoccupied d orbitals.This special electronic and geometric structure enables Rh Au-PdCuPNSs to have excellent ethanol oxidation performance and excellent C1 path selectivity in alkaline media.More empty d orbitals on Pd can enhance the adsorption of CH3 CO intermediates（CH₃CO^*）on Rh Au-PdCuPNSs,thus effectively reducing the breaking barrier of C-C bond in CH₃CO^* and promoting the complete oxidation of ethanol.（2）A general synthesis method of Pd-based alloy nanobelts（NBs）is developed,and PdCuLn NBs（lanthanide Ln）with unique geometric structure are prepared and successfully applied to ethanol oxidation reaction（EOR）and glycerol oxidation reaction（GOR）.The results show that the construction of low coordination active sites significantly enhances the catalytic activity of the catalyst.The change of Ln has little effect on its morphology.Through the comparison of transmission electron microscopy（TEM）images of Pd,Pd Cu,Pd La（lanthanum La）and PdCuLa,it can be seen that the incorporation of Ln is the fundamental reason for the geometrical morphology of PdCuLn NBs.PdCuLn NBs have the advantages of large specific surface area and large number of coordination atoms,which makes its excellent electrocatalytic performance for the oxidation of biomass alcohols.（3）By introducing p-block elements into the PdCuLn structure,the synthesis of PdCuLn Te（P）NBs（tellurium Te,phosphorus P）with d,p,f three-block elements co hybridization are achieved.The results show that the hybridization of d,p,f elements can significantly regulate the electronic structure of Pd,thus improving its EOR and GOR performance.The X-ray photoelectron spectroscopy（XPS）data of PdCuLnTeNBs shows that electrons migrate from Pd 3d orbitals and the unoccupied d orbitals of Pd increase,which could effectively enhance the interaction between Pd and CH₃CO^*,thus greatly reducing the energy barrier of C-C bond breaking and promoting the complete oxidation of ethanol and glycerol.In order to further adjust the electronic structure of Pd,P element is further doped on the basis of PdCuLnTeto form PdCuLnTeP NBs.The morphology of PdCuLnTeP is similar to that of PdCuLn Te.According to the electrochemical performance test results,the EOR/GOR performance of PdCuLnTeP NBs is significantly improved compared with PdCuLn NBs and PdCuLnTeNBs.This indicates that the alloying of Pd with elements in d,p and f blocks improves the electronic structure of the active center Pd.And this optimized electronic structure can regulate the adsorption energy of the reaction intermediates,reduce the activation energy of the chemical reaction,and ultimately improve its catalytic performance.