| With the rapid development of science and technology,the demand for energy is also growing.However,with the depletion of fossil energy and the aggravation of environmental pollution,it is urgent to develop sustainable clean energy and apply it on a large scale.Fuel cell is a kind of device which can directly convert the chemical energy into electric energy.It has almost no pollution to the environment and can also meet our demand for energy.In recent years,the substitution of methanol as a direct fuel for organic small molecular alcohols has attracted widespread attention.For example,researchers have tried to replace methanol with ethanol,ethylene glycol,and glycerin.Among the small molecular alcohols,ethanol has the advantages of lower toxicity,higher energy density,large mass production,negligible anode-to-cathode permeation,etc.It is the most feasible method to increase the reaction rate by using Pt-based catalysts in fuel cell.Although Pt is active for the dehydrogenation process in the alcohol electrooxidation reactions,it still suffers from the sluggishness of the C-C bond cleavage and is easily poisoned by the adsorbed CO(COads),resulting in drastically reduced activity.Moreover,Pt is one of the rarest metals in the Earth's crust causing a super high economic cost.In order to improve the utilization and efficiency of Pt-based catalysts,adjusting the morphology,size and structure of Pt-based catalysts is essential.In this thesis,we use a seed-mediated-growth method to synthesize Rh@Pt core-shell nanocrystals with controllable surface structure.We integrate both the catalytic properties of Rh and Pt and optimize the atomic thickness of Pt shell to prepare catalysts with high activity and stability.The main research contents are as follows:First,we demonstrate a well-designed synthesis of sub-10 nm concavity-tunable Rh@Pt core-shell nanocubes with an engineered Rh-Pt heterointerface and surface Pt atomic steps for EOR catalysis.The surface concavity of the Rh@Pt core-shell nanocubes was successfully manipulated through kinetically mastering the Vdep./Vdiff.ratio of the Pt atoms during the over-growth process.Compared to the Rh@Pt shallow concave nanocubes(Rh@Pt s-CNCs)and Rh@Pt flat nanocubes(Rh@Pt FNCs),the Rh@Pt deeper concave nanocubes(Rh@Pt d-CNCs)have richer surface Pt atomic steps and exhibit a greatly enhanced EOR catalysis activity.Electrochemical in situ FTIR studies indicate that the Rh-Pt interfacial interaction and the higher surface Pt atomic steps on the Rh@Pt concave nanocubes can effectively facilitate the C-C bond cleavage towards a complete oxidation of ethanol to CO2.Next,we demonstrate the successful synthesis of ultrathin Rh@Ptx core-shell nanobranches(Rh@Ptx NBs)with controlled Pt atomic layer number and faithful replication of the high-density grain boundaries of the Rh NB cores on the outermost Pt shells.As the balance of compression strain and ligand effects between the Rh nanobranches and the Pt shells,the EOR performances are highly dependent on the number of the outer Pt atomic layers.We found that Rh@Pt0.21 NBs with less Pt layer had better ability to promote the cleavage of C-C bond.With the increase of Pt shell thickness,the ability of C-C bond cleavage is weakened gradually,while the catalytic activity is on the rise.In general,Rh@Pt0.83 NBs has excellent ability to promote ethanol oxidation and glycol oxidation,making it show the best performance in both mass activity and specific activity.To this end,we have successfully synthesized Rh@Pt core-shell nanocrystals,which exhibit excellent activity and stability in EOR.With Rh and Pt as the main body,Rh@Pt core-shell nanocubes with high index facets and Rh@Ptx NBs with ultrathin branch structure were prepared by effective synthesis methods.It was found that both Rh@Pt core-shell nanocrystals show better activity in EOR. |
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