The Research For Realizing Anode Reaction Mechanism And Improving Anode Catalyst Of Direct Methanol Fuel Cell

Direct methanol fuel cell (DMFC), as a kind of generating set, has the feature ofhigh efficiency, low temperature, safety and convenient fuel storage andtransportation, which can be used as an effective solution to environmental pollutionand energy crisis, andshows broad prospects for development in the field of mobileand portable power. But its internal electrochemical and mass transfer mechanism isnot clear which limits its development, especially for the poisoning problem of anodecatalyst by CO, and dynamic surface adsorption. Study on anodic reaction mechanismcan realize catalytic process, clarify the dynamic changes of the surface adsorptionmaterial and provide direction for the improvement of the catalyst that will makecontribution to high activity, long service life and lower cost of methanol fuel cell.EIS, as a kind of electrochemical measurement, can penetrate into the electrodeprocess kinetics, and study its surface state for its rapid measuring and lowinterference for surface state.It belongs to the category of alternating-currentmeasurement, and has made a significant contribution on the electrochemicalmechanism of judgment. This work will study DMFC anode reaction mechanism,especially the dynamic process of catalyst activity change with EIS technology as amajor means, cyclic voltammetry and chronoamperometry as auxiliary means, and onthe basis of the realization of catalytic mechanism the improvement of catalysts werepreliminary given directions.Firstly, it is put forward that there are three state variables, θ1(the coverage ofCO), θ2(OH) and θ3(PtO), to influence the reaction rate in addition to the potential.Atlow potential the coverage of CO dominates, and with potential rising, CO coveragedecreases and OH coverage increases and transforms into PtO at high potential. According to theory of electrochemical impedance spectrum, the impedanceexpressions under different potentials are deduced and corresponding equivalentcircuit are obtained to make fitting with the spectra. The analysis results show thatwhen the two kinds of state variablesθ1and θ2have a relationship likeθ2＞32/39(1-θ1)and1=2, the change of coverage leads to a negative resistance. Itdraws a conclusion that CO and OH compete on the active site and the coverage ofCO decreases and OH increases with potential rising. When the two kinds of statevariables are equal, oscillation occurs on the parallel branch, directly leading to anegative resistance. and at high potential OH transforms into PtO leading materialcorrosion that could weaken the catalyst activity. For improving catalyst materials,other components are expected to add in Pt catalysts to alleviate competition by COand OH.Then, based on the methanol oxidation mechanism research, Pt/C catalysts arecomposited with H2PtCl6as precursor, coated by aniline. The activity of catalysts inH2PtCl6and aniline molar ratio of1:3,1:5and1:7are investigated using cyclicvoltammetry, chronoamperometry and EIS respectively. The results indicate that thecurrent of methanol oxidation is the largest and the reaction impedance is the leastwhen H2PtCl6and aniline molar ratio is at1:5. Then the highly active catalystsaresintered at400℃,600℃and800℃respectively, a preliminary study on itsactivity experiment results show that the activity of catalyst sintered under600℃increases significantly.