Design, Synthesis And Mechanism Study Of Electrocatalysts For Palladium-based Alcohol Oxidation

Direct alcohol fuel cells(DAFCs)have become one of the most promising energy conversion devices due to their high energy density,small size,and mild conditions.At present,the common catalysts for the anodic oxidation reaction of direct alcohol fuel cells are mainly platinum(Pt)-based materials.However,palladium(Pd)-based catalysts have larger storage capacity,lower cost,and show better reaction kinetics and stronger anti-poisoning ability than acidic media in alkaline electrolytes.Therefore,Pd-based catalysts are gradually developing into a very important type of catalyst in direct alkaline alcohol fuel cells.However,the slow electrocatalytic kinetics makes the catalyst still have the problems of insufficient activity and poor stability,which seriously hinders the wide application of DAFCs.This is mainly because the toxic carbon-containing intermediate produced in the alcohol oxidation process will quickly adsorb on the surface of Pd,thereby deactivating the catalyst.Therefore,the effective removal of the toxic carbon-containing intermediates adsorbed on the surface of Pdis the key to the improvement of electrocatalytic performance.Here,this thesis reasonably designed three main strategies to remove the toxic intermediates adsorbed on the Pd-based catalyst.They include:(i)weakening the affinity of poisoning intermediates on the catalysts by modifying the surface electronic states of Pd(electronic effect);(ii)increasing the number of OH_adsto react with toxic intermediates to achieve the desorption of toxic intermediates(bifunctional effect);(iii)exposing more active sites and facilitating electron/mass transfers by engineering the nanostructures of Pd-based nanocatalysts(structural effect).Taking the improvement of catalyst performance and the utilization of nobel metals as the research goal,three different Pd-based nanocatalysts were designed from the advantages of catalyst structure and components.The growth mechanism,structure/composition and electrocatalytic performance of the designed Pd-based nanomaterials under alkaline conditions were studied and discussed.The main research results are summarized as follows:1.Synergistic effects of interstitial boron in Pd-based nanocatalysts for ethanol oxidation electrocatalysisUsing alloyed boron to optimize the physical and chemical properties of the Pd-based nanocatalyst,the optimized PdCu B nanocatalyst has better electrochemical activity and stability.The focus of this work is to explore the effect of the alloying of metalloid boron and Pd-based nanocatalysts on the electrooxidation catalysis of ethanol in alkaline media,and the mechanism of its catalytic reaction is discussed in depth from the component advantages.2.Synthesis of ternary PdBP alloy nanowires and study on its ethanol electrooxidation performanceBy alloying metalloid and non-metal with the nobel metal Pdand further designing its nanostructure,it can be matched with the design strategy,thereby improving the performance of ethanol oxidation.This electrocatalyst is formed in an aqueous solution via anisotropic nucleation and growth of ternary PdBP alloy nanowires along assembled cylinder template of Plurolic F127 on a nitrogen-functionalized graphene support(denoted as PdBP NWs@N-G).The catalyst can promote the removal and further oxidation of carbon-containing toxic intermediates under the synergistic effect of components and structural advantages,thereby significantly improving the performance of ethanol oxidation.3.Synthesis of asymmetric PdPt Cu mesoporous hemisphere and study on its methanol electrooxidation performanceThe use of precious metals to alloy secondary metals and further design nanocatalysts with more structural advantages can efficiently improve the performance of methanol oxidation.By using amphiphilic dioctadecyldimethylammonium chloride as a mesopore-forming surfactant and nitrogen-functionalized graphene as a symmetry-breaking support,asymmetric multi-element Pd-based mesoporous hemispheres(MHSs)can be formed.These asymmetric multi-metal MHSs exhibit excellent composition and structural advantages,such as expanding the electrochemically active surface area,accelerating electron transfer and material transport,optimizing the CO poisoning resistance,thereby effectively improving the methanol oxidation performance.