Synthesis Of Three-dimensional Pd-based Nanochains And Investigation Of Their Electrocatalytic Properties For Formic Acid And Ethanol

As a clean and efficient energy conversion technology,fuel cells have been gradually recognized and got widespread attention.At present,commercial Pd/C and Pt/C catalysts are mainly used in the market,but the activity and stability of fuel cell catalysts still need to be further improved.For the recent years,researchers have been working to improve the utilization of precious metals and the performance of catalysts from two aspects:one is to alloy Pd with one or more metal elements and non-metallic elements by alloying method;the other is to optimize the structure and corresponding properties of catalyst surface by controlling the morphology of nanomaterials by different synthetic methods.In this paper,we have synthesized different proportions of"clean"3D porous binary and ternary Pd based alloy nanochain networks at 60°C using a kinetic controllable self-assembly method.And the synthesized nanomaterials were treated as promising catalysts,which are been applied to catalyze formic acid oxidation and ethanol oxidation.The main parts are as follows:（1）The binary PdSn alloy and the ternary PdSn P alloy chain networks were successfully synthesized at relatively low temperature（60°C）via a simple self-assembly method.The results show that the composition and type of elements will not affect the formation of such 3D network morphology.Due to the introduction of non-metallic P,the size of the nano-material is obviously reduced.The average particle diameter of the binary PdSn materials is approximately 7nm,while that of ternary PdSn P nanochain networks is only about 4nm.（2）A series of physical characterization analyses show that the binary and ternary materials are face-centered cubic alloy structures.XPS analysis shows that metal Pd and oxidation state Sn are the main components of PdSn alloy materials.XRD shows that the crystallinity of PdSn P alloy materials is significantly reduced compared with PdSn materials,which is related to the introduction of nonmetallic P.According to the Scheler formula,the particle sizes of binary material and ternary material are calculated to be about 7nm and 4nm respectively.The result is the same as the TEM observation results.（3）Under acidic conditions,we use the prepared binary and ternary alloy materials to catalyze the electro-oxidation of formic acid.The results manifest that the catalytic activity and stability of PdSn and PdSn P alloy materials are much superior to those of commercial Pd/C.Specially,Pd₂Sn₁ and Pd₂Sn₁P₁ show the most significant catalytic abilities.The improvement of material properties is related to its relatively large active surface area.The Pd₂Sn₁P₁ has larger catalytic activity compared with Pd₂Sn₁,which can be ascribed to their smaller size,larger surface area of electrochemical activity and better electron interaction between atoms.（4）Under alkaline conditions,we apply binary and ternary alloy materials to the ethanol oxidation,respectively.The experiment shows that all binary PdSn and ternary PdSn P alloy materials have better activity and stability than commercial Pd/C.The significant improvement in properties is due to the influence of alloy effect and morphology.Take Pd₂Sn₁ as an example to study the difference of catalytic oxidation of formic acid and ethanol,the results show that the catalytic activity of the Pd₂Sn₁ for ethanol oxidation is lower than that for formic acid,but the stability of it for ethanol is significantly improved than that for formic acid.This is because ethanol is more difficult to oxidize than formic acid,and the C-C bond is difficult to break;but under alkaline conditions Pd it is not easy to dissolve,and the stability is obviously enhanced.