The Spe Water Electrolysis And Pemfc Electro-catalyst Preparation And Performance

Based on the research status of the electrocatalysts for Solid Polymer Electrolyte(SPE) water electrolysis and Proton Exchange Membrane Fuel Cells(PEMFC),a series of studies in relation to SPE techniques were carried out;1)five kinds of Membrane Electrode Assembly(MEA)were made,and their properties of SPE water electrolysis and H/D isotope separation were examined; 2)Pt/C,Pt-Pd/C,Pt-Ir/C,Pd-Ir/C and Pd/C catalysts were synthesized by microwave heating polyol method,and were characterized by TEM,XRD,EDS and XPS; 3)Ag/SPE plates were obtained by impregnation-reduction method,and many factors influencing on the plates were investigated.The following innovative conclusions were gained.The performances of IrRu/Nafionl 17/PbAg,IrRu/ Nafionl 17/Ni,IrRu/Nafionl 17/TiNi₃, Ag/Nafionl 17/Ni and C/Nafionl 17/PtRu MEA for SPE water electrolysis were investigated. It was revealed that the order of water electrolysis activity was IrRu＞Ag＞C for anodic catalysts and Ni＞PbAg＞TiNi₃ for cathodic catalysts.TiNi₃ was less stable than PdAg, however,much more stable than Ni.Overpotentials of these electrodes descended with the increase of temperature.Meanwhile,the current efficiency rose with the augment of current density.SPE water electrolysis was applied to H/D isotope separation.The separation factors of H/D isotopes for IrRu/Nafionl 17/PbAg,IrRu/Nafionl 17/TiNi₃,IrRu/Nafionl 17/Ni and C/Nafionl 12/Pt-TiO₂ MEA electrodes at 40℃and 90 mA·cm^-2were 4.49,3.48,3.14 and 4.53, respectively.The results of the IrRu/Nafionl 17/PbAg electrode experiments also showed that the separation factors went up with the increase of current density,but down with the increase of temperature.The fit line of lnα～10³/T was lna=0.816×(10³/T)-1.112,and the calculated activation energy was about 6778 J·mol^-1between 40℃and 70℃.The preparation process of the Pt/C electrocatalyst by microwave heating polyol method was surveyed comprehensively.The size and distribution of Pt nanoparticles greatly depended on microwave irradiation duration.The Pt/C catalysts derived from microwave irradiation for 90s was uniform in size(about 3.0～4.5nm),non-agglomerated,well dispersed on carbon supports,and the reaction was comparatively thorough.The Pt/C catalyst obtained by the twice microwave irradiation for 90s(60s on+30s off+30s on)was better than that by the one-off microwave irradiation for 90s.The pH values of ethylene glycol solutions affected the sizes and uniformity of Pt nanoparticles and their dispersion on the surfaces of carbon support surfaces.The results showed that the average sizes of platinum nanoparticles decreased from 4.2nm to 3.2nm with the increase of pH values from 1.99 to 10.23 for Pt/C.In addition, increasing pH values of ethylene glycol solution could improve the uniformity and dispersity of platinum nanoparticles on carbon surfaces.Pt/C,Pt-Pd/C,Pt-Ir/C,Pd-Ir/C and Pd/C catalysts were prepared by microwave heating polyol method.In order to contrast,Pt/C was also synthesized by the conventional impregnation reduction method.XRD analysis indicated that the structures of the Pt/C by two methods were both faced-center cubic crystal,and the peak shapes of Pt-Pd/C and Pd/C were similar to that of Pt/C.Moreover,combined XRD with electronic diffraction spectrum,the structures of Pt/C,Pt-Pd/C and Pt-Ir/C were single-crystal,polycrystalline and non-crystalline,respectively.Analyzed by XPS,the relative content of Pt(0)in the catalysts containing Pt synthesized by the new method was more than 60%.The oxidate Pt of Pt-Ir/C was less,the high valence Pt was much less,and PtO₂ was almost inexistent.In contrast,the relative content of Pt(0)of the Pt/C catalysts synthesized by the conventional method was lower,and the oxidate state Pt was more.The mechanisms of the beneficial effect of the new method on the catalysts were studied to some extent.It may be because that the new method could improve the uniform size,the specific surface area and the dispersity and the active sites of Pt metallic atom.At the same time,the new method could also reduce the Pt oxide which was no catalysis and yet hindered the absoption of H₂,CH₃OH,OH and O₂.Hence, compared with the conventional method,the new method could enhance the catalytic activation of the catalysts.The preparation process of the Ag/SPE plate by impregnation-reduction method was also investigated.The results showed that the particle size of the plate was larger and the dispersity was worse.The plate was more compact with the increase of the concentration of Ag⁺ or BH₄^- ion.However,if their concentration is too high,it will cause much too thick plate which can hinder the transfer and diffusion of the gases.When the plating time was selected once, the Ag/SPE plate at 3×10^-3mol/L Ag⁺ and 0.1 mol/L(pH=13)BH₄^- ion was fine,and the average size of Ag panicle was about 41.2nm.When the concentrations of Ag⁺ and BH₄^- ion were 3×10^-3and 0.1 mol·L^-1(pH=13),the average size of Ag panicle on the layer with twice plating was about 52.2nm,and the layer was fine and compact.