Preparation Of Platinum-palladium Nanostructured Catalysts And Their Oxygen Reduction Properties

Fuel cell is a new energy conversion system with high efficiency and cleanness.It can directly convert the chemical energy of fuel into electric energy without going through Carnot cycle.In addition,the reaction between fuel and oxygen has no emission of gas pollutants and is environmentally friendly.Nowadays,the problem of environmental pollution and energy exhaustion is becoming more and more serious,so the development of high efficiency fuel cell can kill two birds with one stone.Therefore,fuel cells have been developed rapidly in recent years.Especially,proton exchange membrane fuel cell?PEMFC?is considered to be the most promising future power source of automobile and attracted more and more attention.However,high over-potential of cathodic oxygen reduction and complex kinetic conditions greatly hindered the development of PEMFC.In addition,single metal platinum catalyst still has high cost,poor stability and other problems.The precious metal alloy catalyst with specific morphology can improve the electrocatalytic performance by regulating the surface structure and electronic structure of the material.In this thesis,Pt-Pd nano-structured catalysts with different morphologies have been synthesized efficiently and low-cost by a simple one-pot synthesis method,and their physicochemical properties as cathode oxygen reduction catalyst were studied.The specific contents and conclusions are as follows:?l?One-pot synthesis of Pt-Pd bimetallic nanodendrites with enhanced electrocatalytic activity for oxygen reduction reaction In this thesis,we report a facile one-pot method by tuning the feed ratio of Pt and Pd?Pt₃Pd,,Pt₂Pd,,and Pt₁Pd₁?in ethylene glycol solution,at the effect of iodide ions and poly?vinylpyrrolidone??PVP?to synthesize three different Pt-Pd bimetallic nanodendrites structures.Trans:mission electron microscopy?TEM?and high-resolution transmission electron microscopy?HR-TEM?reveal that the nanodendrites have a Pt-rich surface structure and numerous high-index facets at the branches surface,thus provided a great deal of catalytic sites.Carbon supported Pt-Pd nanodendrites catalysts is investigated for oxygen reduction reaction?ORR?performance and accelerated durability test?ADTs?.The Pt1Pd1/C catalyst shows the best activity and durability,and with a mass activity of 1.164 A mg^-1_pt and a specific activity of 1.33 mA cm^-2,which is 7.76-and 5.32 times higher than commercial TKK-Pt/C catalysts.At the same time,when compared with Pt/C catalysts,three kinds of Pt-Pd nanodendrites catalysts have better durability.These results provide us an attractive strategy for designing catalysts with a simple route,lower cost and remarkable catalytic activity and durability.?2?Facile synthesis of bimetallic Pt-Pd symmetry-broken concave nanocubes and their enhanced activity toward oxygen reduction reaction In the present work,we report a facile one-pot synthesis route to obtain Pt-Pd symmetry-broken concave nanocube?SBCNCs?structures in N,N-dimethylformamide?DMF?solutions under the effect of iodide ions and poly?vinylpyrrolidone??PVP?.By given the inhibiting effect of no stirring during the reaction process,and the capping agent effect,newly formed atoms is expected to accumulated at the vertexes and/or edges of nanocube,leading to the formation of the Pt-Pd SBCNCs,which is thoroughly physicochemically and electrochemically characterized.It is found that the specific structure of Pt-Pd SBCNCs are composed of various high-index facet?{210},{310},{410},{610},{720}?and Pt-rich surface.These features enable superior performance for the oxygen reduction reaction,and the specific/mass activities of the Pt-Pd SBCNCs are 7.7/6.2 times higher than commercial TKK-Pt/C,respectively.It also exhibits a remarkable durability by only reduced 30 mV half-wave potential after 15,000 accelerated durability test?ADTs?cycles.This work provides an effective and simple strategy to rationally design electrocatalysts with enhanced activity and durability toward oxygen reduction reaction or other practical applications.