New Carbon-based Materials Promoted Pt Electrocatalyst For Methanol Oxidation

With the shortage of fossil fuels and environmental pollution problems becoming more and more serious,researchers are trying to develop a new energy source.The direct methanol fuel cells（DMFCs）have attracted widespread attention due to the advantages of high energy exchange efficiency and the environmental friendliness,while the high price of noble metal（Pt）as catalyst restricts the application of DMFCs.Recently,catalyst supports and promoters have been attached much importance to be used to reduce the use level of Pt metal.Therein,porous carbon,carbide and heteroatom dopant have remained the research focus.In this paper,porous graphite（graphene）,angstrom-scale vanadium carbide,bamboo-like nitrogen doped tungsten carbide are prepared as catalyst supports to improve the use ratio of Pt and improve the interaction force between supports and Pt nanoparticles.Therefore,both the higher catalytic activity and stability of the Pt based catalysts for catalyzing methanol oxidation has been obtained.1.Bowl-like porous graphite（GLB）is synthesized with the solid core mesoporous shell silicas（SCMSSs）as template,glucose as carbon source,NiCl2 as graphitization catalyst.The bowl-like porous carbon（BLC）is also obtained for comparison.Pt nanoparticles are loaded on both the materials to get the Pt/GLB and Pt/BLC catalysts.The physical characterization results show that the diameter of the GLB is the same with that of the SCMSS,indicating the perfect cast process between the GLBs and the SCMSSs.The porous structure and the high surface area of the GLBs favor the uniform dispersion and small-sized Pt particles.The electrochemical characterization results show that the peak current density on the Pt/GLB(2075 mA mg_Pt^-1)is 2.87 times that on the Pt/C(723 mA mg_Pt^-1)and 1.12 times that on the Pt/BLC(1846 mA mg_Pt^-1).Moreover,the Pt/GLB has excellent stability and antitoxic properties.2.Carbon-vanadium carbides（C-V₈C₇）with controllable shapes are synthesized by adjusting the ratio of the sodium vanadate to the ion-exchange resin.With the increase ratio of the sodium vanadate,the shape of V₈C₇ transform from rod with an average width of 0.8 nm to nanoparticle shape with a diameter of 10 nm.Pt nanoparticles are loaded on the materials to get the corresponding Pt/C-V₈C₇ catalysts.The electrochemical results show that the peak current density of the rod-shaped Pt/C-V₈C₇(1605 mA mg_Pt^-1)is 1.78 times that of particle-shaped Pt/C-V₈C₇(1377 mA mg_Pt^-1),and 2.07 times that of the commercial Pt/C（775 mA mg Pt-1）for the methanol oxidation reaction.More significantly,the current density of the rod-shaped Pt/C-V₈C₇ is 9 times that of the Pt/C at 0.4 V,indicating the high advantage of the former at the lower potential.In addition,both the Pt/C-V₈C₇ catalysts have higher catalytic stability than the Pt/C.The electron transfer exists between carbides and noble metals,changing the surface electronic structure of Pt and improving interaction force between support and Pt,thus leading to improved electrocatalytic activity and stability for the methanol oxidation.3.Nitrogen doped tungsten carbide（NWC-1）is synthesized with melamine as nitrogen source and carbon source and ammonium metatungstate as tungsten source.A modified nitrogen doped tungsten carbide（NWC-2）is also synthesized by adding FeCl₃,which make NWC-2 have high graphitization degree and conductivity.Pt nanoparticles are loaded on the materials to form Pt/NWC-1 and Pt/NWC-2 catalysts.The Pt particles in both the Pt/NWC-1 and Pt/NWC-2 are around 1.0 nm.The existence of Fe element make both the WC in the NWC-2 and the loaded Pt particles on NWC-2 more uniform.The electrochemical characterization results show that the Pt/NWC-2 has higher catalytic activity,stability and conductivity than the Pt/NWC-1,which are resulting from the higher graphitization degree and more uniform structure of the NWC-2.