Performance Of Vertically Oriented Graphene Supported Pt-Ru Bimetallic Catalyst For Methanol Oxidation

Direct methanol fuel cells (DMFC) are commercially attractive due to the significant advantages beyond external reformation-hydrogen counterparts in the handling, transportation, and storage of fuels. Considering the slow kinetics of methanol oxidation reaction (MOR), the exploration and development of effective anode catalysis deserve continuous scientific endeavors to be directed toward. Pt metal is considered as the most powerful anode catalyst for methanol oxidation for many years, however, Pt which is expensive and infrequent will be poisoned by the immediate of methanol oxidation, such as CO. Pt-Ru bimetallic catalyst is an outstanding candidate as a DMFC anode catalyst since it shows high catalytic activity for methanol oxidation reaction and strong tolerance against poisoning species. It is noted that the electrocatalytic activity of Pt-Ru catalysts on the methanol oxidation is not strongly dependent on their sizes and distribution of Pt-Ru particles. Thus, the supporting materials with high specific surface area are essential to disperse catalyst particles and improve the efficiency of metal catalysts. Based on this, the research contents and results of this thesis are as follows:The electrocatalytic performance of vertically oriented graphene (VG) supported Pt-Ru bimetallic catalysts toward methanol oxidation reaction (MOR) were reported. Dense networks of VG were directly synthesized on carbon paper (CP) via a microwave plamsa-enhenced chemical vapor deposition (PECVD) method. A repeated pulse potentials approach was applied in a conventional three-electrode electrochemical system for the co-electrodeposition of Pt-Ru bimetallic nanoparticles. It provided a facile alternative for the controllable deposition of Pt-Ru catalysts with different Pt and Ru molar ratios by change the precursor salt concentration in the electrolyte.Based on inductively coupled plasma mass spectroscopy (ICP-MS) and scanning electron microscopy (SEM), it is found that, the decoration of VG can simultaneously lead to a ～3.5 time higher catalyst mass loading, a ～50% smaller nanoparticle size and a better dispersion than the pristine CP counterparts (about 50 nm on VG and 100 nm on CP).An optimum Pt molar ratio of 83.4% in the deposits, achieved with a [H2PtCl6]: [RuCl3] of 1:1 in the electrolyte, was clarified with synthetically considering the mass specific activity, CO tolerance, and catalytic stability. According to Tafel analysis and cyclic voltammetry (CV) tests, the Pt-Ru/VG catalyst with the optimized Pt molar ratio can realize a faster methanol dehydrogenation than Pt/VG, and present a significantly enhanced catalytic activity (maximum current density of 339.2 mA mg-1).In the comparation with pristine CP and commercial Vulcan XC-72 as the supports, it was observed that, the Pt-Ru/VG catalyst possessed of a maximum current density of 339.2 mA mg-1, significantly higher than those of Pt-Ru/CP and Pt-Ru/Vulcan (116.3 and 192.8 mA mg-1,respectively). Moreover, the optimum Pt-Ru/VG catalyst presented a much enhanced catalytic activity toward MOR and catalyst tolerance to the poisoning species.