Synthesis And Study On Electrocatalytic Properties Of Bimetallic PdAu Nanoflowers

Noble metal catalysts,as a type of heterogeneous catalysts,are widely used in various chemical reactions.However,the catalytic activity of heterogeneous catalysts depends on the interaction between the atoms on the catalyst surface and the intermediates in the key steps of the reaction,and the catalytic activity of the catalyst can only be optimized when the interaction between the atoms on the catalyst surface and the intermediates is neither too strong nor too weak.d-band center theory,which regulates the interaction strength by adjusting the electronic structure of the catalyst surface,provides us with a good idea to design high-performance catalysts.When the energy difference between the d-band center and the Fermi energy level is small,the d-band center is higher and the adsorption energy of surface atoms and intermediates is larger;conversely,when the d-band center is lower,the adsorption energy is smaller.The results of extensive experiments and theoretical calculations have proved that the electronic structure can be controlled to improve the catalytic activity by modulating the element composition,strain engineering,particle size,specific morphology and crystal planes.We propose a simple aqueous method to synthesize flower-like bimetallic Pd Au nanocatalysts with controllable Pd/Au molar ratio,and the obtained nanoflower catalysts were used as a research object to systematically investigate the electrocatalytic performance of methanol oxidation.Through the characterization and analysis of the morphology,structure,elemental composition and state,we found the modification effect of Au on the d-band center of Pd and the existence of intra-atomic and/or inter-atomic charge transfer between Au and Pd.Subsequently,the samples were tested for methanol electrocatalytic oxidation performance in comparison with commercial Pd/C catalysts,and the test results showed that the catalytic performance of Pd Au nanoflower catalysts was significantly enhanced compared with commercial Pd/C catalysts,mainly because the introduction of Au effectively modulates the d-band center of Pd;Pd₁Au₁nanoflower catalysts have the optimal electrocatalytic activity for methanol oxidation,because a large amount of Au would occupy the active sites that Pd could provide,thus reducing the reaction rate.Subsequently,we made Pd₁Au₁ nanoflower catalysts into Pd H_0.43Au nanoflower catalysts and investigated their electrocatalytic performance for alcohol oxidation in order to further improve the catalytic activity of the samples.By analyzing the X-ray diffraction patterns and surface structures of the samples,we found that the diffraction peaks of the Pd H_0.43Au nanoflower catalyst were slightly shifted and the lattice was slightly expanded compared with that of the Pd₁Au₁nanoflower catalyst,which were strong evidence for the penetration of H atoms into the Pd Au alloy to form hydrides.Then the Pd H_0.43Au nanoflower catalyst was tested for alcohol electrocatalytic oxidation performance in comparison with the Pd₁Au₁ nanoflower catalyst,and the test results showed that the catalytic performance of the Pd H_0.43Au nanoflower catalyst was further enhanced,which can be attributed to the fact that the downward shift of the d-band center caused by the penetration of H atoms into Pd weakens the binding strength between the Pd H_0.43Au nanoflower catalyst surface and the reaction adsorbate.It is also further demonstrated that the catalytic activity of the catalyst can be effectively enhanced by modulating the electronic structure of the catalyst surface.