Research Of Ordered Membrane Electrodes Based On PANI-Pt Nano-array Structure

In the electrochemical energy conversion devices,the oxygen reduction is considered the main limitation step of energy conversion efficiency.For example,polarization loss is account for 76%of the entire fuel cell loss in the proton exchange membrane fuel cell.Moreover,the noble metal catalyst used in oxygen reduction reaction is also an important constrained factor in the practical application of these electrochemical energy conversion devices.It costs only 0.05 mg/cm² of noble metal platinum in the fuel cell anode hydrogen oxidation process.However,in the oxygen reduction reaction,the total mass of the platinum is about 0.4 mg/cm² in the commercial cathode electrodes.This is far greater than the entire electrode?cathode and anode including?energy target amount of 0.125 mg/cm² expected by the US Department.The ordered array electrode with surface directed nano-array structure catalyst was gradually developed to improve the performance of the oxygen electrode reduction reaction.This array electrode with a low platinum loaded of 0.15 mg/cm² in the cathode was produced by 3M Company and it exhibited excellent electrical output performance.In contrast to the conventional Pt/C?platinum content:0.4 mg/cm²?electrode,the performance of this new electrode demonstrated a similar output with much lower platinum content.Therefore,the ordered array electrode is the most promising to become the next generation electrode.To achieve this aim,this thesis is mainly focused on the preparation and characterization of PANI-Pt?Polyaniline-platinum?nano-array electrode and the contexts are summarized in the following:?1?The polyaniline nano ordered arrays were prepared in a control fashion using the stairs-current polymerization method.Summing up all the parameters affecting the electrical polymerization reaction in the preparation of polyaniline nano ordered arrays,the concentration of perchloric acid and aniline,electric power during the polymerization current density and polymerization time were investigated under different conditions in this thesis.The growth mechanism of olyaniline nano ordered arrays can be explored according to the change of the diameter,length and density of the obtained nanoarrays under different condition.It was found that the key parameters for the growth of polyaniline nano ordered arrays are the concentration of perchlorate and the polymerization time.The nanoarrays can't be formed with the concentration of perchlorate below 0.4 mol/L or aniline solution below 0.05 mol/L.The growth of polyaniline fiber was too fast to form the cross-linking fiber network films when a high current density was applied.The polyaniline nano ordered arrays with fiber diameter of 33 nm,length of 180 nm and density of 244?1/?m²?,can be prepared in an optimized condition.?2?The deposition of platinum on the glassy carbon electrode surface was investigated.It was found that the platinum nanoparticles with size more than 10 nm were deposited on the glassy carbon surface under different potentials and a constant-voltage condition.The reason for the big particle size can be attributed to the low nucleation sites caused by the low surface area of the planar structure.Therefore,to achieve the platinum nanoparticles with a smaller size,the morphology of the glassy carbon need to be optimized to increase the nucleation sites.Under the deposition potential of 400 mV,the nucleation of platinum nanoparticles is continuous and their growth are controlled via the diffusion.?3?PANI-Pt_ED ordered nano-array electrode was prepared by the deposition of Pt nanoparticles on ordered PANI nano-array under an over-potential and constant voltage of 400 mV and a PANI-Pt_ED ordered nano-array electrode with fiber length from 184²05 nm,density of 89¹36?1/?m²?,and diameter in the range of 52⁶9 nm was obtained.The results showed that PANI-Pt_ED ordered nano-array electrode demonstrated high electrochemical activity and high potential stability.The limiting current density using this electrode is around 6 mA/cm² and the electrode loss is less than 20%after a test time of 20000 s under a high potential of 0.65 V.A specific activity up to 718.36?A/cm²_pt and mass activity of 0.0771 A/mg_pt were achieved using this electrode,?4?PANI-Pt_SD ordered nano-array electrode was also successfully prepared by the deposition of Pt nanoparticles on ordered PANI nano-array via magnetron sputtering technology.PANI-Pt_SD ordered nano-array electrode with fiber length from190²19 nm,fiber density at 50⁶5?1/?m²?,diameter from 77¹35 nm was obtained.Using this electrode,specific activity and mass activity up to 65.81?A/cm²_pt and0.0534 A/mg_pt were achieved.?5?Three dimensional ordered macroporous silicon?3DOM?incorporated with inorganic Cs_2.5H_0.5PW electrolyte was prepared and used as high temperature proton exchange membrane materials.The results showed that this electrolyte membrane demonstrated high conductivity,good stability and low activation energy.Within an incorporated Cs_2.5H_0.5PW content of 90 wt.%,the electrolyte membrane performed an conductivity of 0.228 S/cm under 170?.