Study On Synthesis, Characterization Of Pl Atinum-Based Anode Cataiysts And Their El Ectrocatalytic Activity For Direct Methan Ol Fuel Cell

The direct methanol fuel cell (DMFC) is considered as a promising green technology for the portable and stationary energy sources due to its high energy conversion efficiency, low carbon emission and ease of handling, storage and transportation. Platinum is the common anodic catalyst because it can facilitate methanol oxidation most effectively in DMFC. However the prohibitive high cost and CO poisoning of Pt metals impede the commercialization of DMFC. In addition, the agglomeration of Pt metals during long-term operation lead to losses in catalytic efficiency of methanol electrooxidation. Therefore, the economical and efficient use of Pt-based catalysts should be taken into account when DMFC were constructed. And towards this end, it is necessary to maximize the activity of Pt-based catalyst.In order to improve the electrocatalytic activity of Pt-based catalyst for DMFC, engineering the size or morphology of Pt nanostructure, adding second component or selecting supports for Pt-based catalyst are used in this dissertation. The main points were described as follows:(1) PMo/PtPd/MWCNT catalysts was synthesized by sonication and ethane diol reduction. PtPd nanoparticles were homogeneously deposited on the surface of Multiwalled carbon nanotube (MWCNT) in high density with assistance of phosphomolybdic acid (PMo). The size of PtPd nanoparticles can be controlled by tuning the composition of PtPd nanoparticles in the presence of PMo. Amo ng these Pt or PtPd catalysts, smallest PtPd nanoparticles can be obtained whe n prepared at Pt/Pd ratio=4. Their average diameter is1.9nm. The as-preared PMo/Pt4Pd1/MWCNT catalysts show largest electrochemical active surfaces and highest current density corresponding to methanol electrooxidation. For compari son, PtPd nanoparticles were prepared and decorated on the surface of MWCN Ts in the absence of PMo. Their average diameter is about7.2nm, and their distribution is not uniform, and most of them form a large one. A comparison between PMo/Pt4Pd1/MWCNT and Pt4Pd1/MWCNT catalysts was curried out by CO stripping voltammetry, it reveals PMo is beneficial to oxidative removal of adsorbed CO at Pt active site. The effect on CO tolerance of Pt catalysts by P d content is also investigated. As compared to PMo/Pt/MWCNT catalysts, Pd c ontent can greatly enhance the current ratio of methanol and CO oxidation duri ng methanol decomposition, indicated that the promoting effect of Pd on CO-to lerance may originate from its high activity toward the cleavage of C-H.(2) A novel approach was developed to synthesize PtIr or Pt nanowires (N Ws)supported on the reduced graphene oxide (RGO) using Te NWs as templat e based on the replacement reaction. The resulting RGO-supported PtIr and Pt electrocatalysts were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy and electrochemical techniques. TEM imag es show that these Pt based catalysts are uniformly distributed in the matrix gr aphene with a characteristic of one-dimensional (ID) nanoporous structure, elect rochemical techniques shows:these ID nanoporous PtIr/RGO (or Pt/RGO) hybr ids exhibit an enlarged electroactive surface and enhanced catalytic activity tow ard the methanol reaction relative to those PtIr or Pt NWs without graphene s upport. Ir introduction can better electro-chemical stability of Pt catalysts and t hus improve poisoning tolerance of Pt anodes.(3) One-dimensional(1D) PtIr nanowires(NWs) was prepared by adding the second element iridium on the basis of platinum. The preparation strategy for1D PtIr NWs is as the fllowing:Ir NWs were used as seeds to direct the gro wth of Pt upon the reduction of K2PtCl4by ascorbic acid (AA) in aqueous sol ution. TeNWs were used as both reducing agent and sacrificial template for ob taining Ir NWs in aqueous solution. for comparison, Pt NWs also was synthesi zed. Pt catalysts were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy. Meanwhile, the catalytic activity of Pt cat alysts on methonal electro-oxidation was explored and compared by cyclic volt ammetry and chronamperometry. The results showed that PtIr NWs exhibited b etter electrocatalytic activity than Pt NWs on methonal oxidation.