Preparation Of Ternary Pt-based Nanocomposites And Its Catalytic Behavior Toward Oxygen Reduction Reaction

Proton exchange membrane fuel cell?PEMFC?has the advantages of high efficiency,less pollution and renewability,it is critical to solve the problems on energy crisis and environmental pollutions.However,the high price,poor durability and anti-poisoning ability of Pt/C cathode electrocatalysts for PEMFC restrict its commercial applications.Thus,the search for highly efficient cathode electrocatalyst contained low content of Pt and long durability has become the hot research spot at present.The purpose of this thesis is to prepare ternary Pt-based nanocomposite catalysts with low price and high activity,and to improve the catalytic performance toward cathodic oxygen reduction reaction?ORR?through adjusting the elemental compositions and the support materials of the catalysts.The electrocatalytic mechanism is also investigated for scientific insights.This work contains three parts.?1?The catalytic properties of carbon supported Pt-based nanocomposite catalysts are studied towards ORR.The Pt-based nanocomposite catalysts of different components?PtCo/C,PtCoTe/C,PtCoFe/C?are prepared through ultrasound-assisted solvothermal method,the prepared catalysts are used as cathode electrocatalysts in PEMFC.For comparison,commercial Pt/C catalyst is investigated under the same test condition.As for the catalytic activity towards ORR,the values of ECSA of PtCoFe/C and PtCoTe/C ternary electrocatalysts reach 19 m²·g_Pt^-1 and 15 m²·g_Pt^-1 respectively,which are 1.5 and 1.2 times as large as that of PtCo/C electrocatalyst.Furthermore,by comparing the carbon support Pt-based nanocomposite catalysts prepared in this experiment,PtCoFe/C catalyst displays the excellent electrocatalytic activity,anti-methanol poisoning and conductivity,and its half wave potential reaches to 550mV which is 100 mV and 20 mV more positive than that of commercial Pt/C and PtCoTe/C catalysts respectively.Regarding on the electrocatalytic mechanism,the ORR on the surface of PtCoFe/C catalyst takes a four-electron process,suggesting higher electrocatalytic efficiency and activity.The enhanced activity towards the ORR also suggests that the introduction of Te takes positive effect on the modification of the valence electrons of Pt and the size effect between Pt-Pt atoms.What's more,the good electrocatalytic activity and durability are derived from the synergy between the three metallic elements and the increased active sites.To be short,low-cost,low Pt-containing and highly efficient electrocatalysts have been developed by changing the components.?2?The catalytic performance of WC enhanced Pt-based nanocomposite catalysts are studied towards ORR.The PtCo/WC/C,PtCoFe/WC/C and PtCoTe/WC/C electrocatlysts are prepared through the intermittently-microwave-heating method,ultrasound-assisted and solvothermal method.As the catalytic activity towards ORR,the values of ECSA of PtCoFe/WC/C and PtCoTe/WC/C ternary electrocatalysts are24 m²·g_Pt^-1 and 22 m²·g_Pt^-1 respectively which are 1.3 and 1.2 times as large as that of PtCo/WC/C electrocatalyst.As for these Pt-based electrocatalysts,PtCoFe/WC/C manifests better activity and the ability of anti-methanol poisoning towards ORR and smaller resistance,and the half wave potential and onset potential are 20 mV and 84mV more positive than those of PtCoTe/WC/C electrocatlysts respectively.In addition,the ORR on the surface of PtCoFe/WC/C catalyst takes a four-electron process.Based on the systematic analysis,the introduction of Te and Fe takes certain effects on the arrangements of the valence electrons of Pt atoms,thus the synergy between WC and Pt are enhanced,leading to the improved the electrocatalytic properties of Pt-based catalysts.?3?Through the researches on the effects of carriers on the electrocatalytic activity of Pt-based catalysts,we find out that the WC can increase the disposed active sites of Pt,leading to the enhanced synergy between WC and Pt,the quasi-Pt effect and the ability towards anti-methanol poisoning.In this thesis,towards ORR,the ternary Pt-based catalysts with certain components and carriers have been modified to abtain high catalytic activity,stability and the ability towards anti-methanol poisoning,which is inspiring and empirical to solve the existing problems in the common Pt/C catalysts and has great potential in the applications of PEMFC cathode catalysts.