Controlled Synthesis Of Pd-based Multimetallic Nanocrystals And Their Electrocatalytic Properties

Due to their outstanding catalytic properties, Pd-based binary and ternary nanocrystals have been widely used in proton exchange membrane fuel cells, especially in the application of methanol oxidation（MOR）, formic acid oxidation（FOR） and oxygen reduction reaction（ORR）. As well known, the performance of Pd-based nanocrystals is mainly determined byit’s size, shape, composition, and structure.Thus, the electrocatalytic properties of Pd-based nanocrystals can be tuned by designing their composition, morphology, and structures.We have developedseveral facile approaches to the synthesis of Pd-based nanocrystals with various specific shapes and compositions, including PdCu alloy nanodendrites, PdCu alloy truncated octahedra, and PdCu@PtPdCu core-shell structures. The growth mechanismsas well as their catalytic properties of methanol oxidation and formic acid oxidationhave beencarefully investigated. The main innovative results are decribed as follows:（1）We developd a facile, one-step approach for the synthesis of PdCu alloy nanodendrites with controllable composition in benzyl alcohol with W（CO）₆ as a strong reducing agent. The composition of PdCu (including Pd₇₇Cu₂₃, Pd₆₅Cu₃₅, Pd₄₈Cu₅₂, Pd₄₃Cu₅₇, and Pd₃₅Cu₆₅) nanocrystals can be controlled by varation of the mole ratios of the Pd and Cu salt ptecursors supplied in the synthesis. PdCu alloy nanodendrites exhibit the substantially enhanced catalytic properties towards MOR in an alkaline media relative to the commercial Pd/C. For example, the specific activity and mass activity of Pd₃₅Cu₆₅is as high as 9.3 times andl.6 times thoseof the commercial Pd/C,respectively.（2）We developd a facile, one-step approach for the synthesis of PdCu alloy truncated octahedron, and PdCu@PtPdCu core-shell structure with controllable composition(varied from PtoPd₅₁Cu₄₉ to Pt₁₉Pd₄₁Cu₄₀, Pt₃₁Pd₃₅Cu₃₄ and Pt₄₄Pd₂₈Cu₂₈) in the presence of benzyl alcohol and DMF. The underpotential deposition （UPD） and galvanic replacement plays a key role for the formation of PdCu@PtPdCu core-shell structure. PdCu@PtPdCu core-shell nanocrystals exhibit enhanced catalytic peformance towards FAOR relative to the commercial Pt/C.Specifically, the Pt₁₉Pd₄₁Cu₄₀ core-shell nanocrystals achieve the highest specific activity and mass activity, which is about 8.1 and 1.4 times as high as those of the commercial Pd/C, respectively.