Fabrication And Characterization Of Pt Catalyst On PANI/Nano Carbons Composite Carriers With High Surface Activity

With the rapid development of technology and economy, the energy crisis and environmental problems are received increasing attention. Fuel cell as the "Clean Energy In the 21st Century" is increasingly becoming a concern and research focus. Direct methanol fuel cell (DMFC),using methanol as fuel, being abundant sources, low prices, liquids at room temperature, easy to carry and store and higher energy density will be more attractive than the hydrogen fuel cells as a kind of proton exchange membrane fuel cell (PEMFC),anode catalyst is a key component of DMFC. Currently, platinum (Pt) is the best catalyst of the system, but the low-efficiency and CO poisoning are the two major problems. In light of these problems, this paper has prepared Polyaniline/nano-carbon composite materials with high surface activity followed by depositing platinum metals on the surface to improve the utilization; The synergy between Pt particles and polyaniline promoted the ability of anti-CO poisoning,which has provide theoretical support for the application of the polymer/inorganic composite materials in DMFC.1. Preparation and Characterizations of the Composite Carriers and CatalystsAt the aspect of the carriers,we have prepared Polyaniline/nano-carbon composites (PANI/XC-72 Carbon and PANI/multi-walled carbon nanotube,PANIMWNT)materials using In-situ polymerization through the structure designation of the composites,meanwhile,tested and analyzed them by the instruments of conductivity,SEM,FT-IR and XRD.SEM showed that the PANI/C, PANI/C ratio of 0.08 and 0.12 show a high surface of complex state, When PANI / C ratio increased (eg. 0.28 and 0.44/) ,the PANI present massive random or nanowires intertwined; In PANI/MWNT system. PANI/MWNT composite with the ratio of 0.54 showed homogeneous polymer-coated carbon nanotubes form.Too small with not saturated polymer loading, resulting nanotube mutual adhesion; and too large with too much polymer coating on the MWNT, showing a great degree of reunion and a large block structure.FT-IR showed that in the PANI/C, the relation between matrix and modifier is conjugate between carbon and N=Q=N structure in PANI.The intensity ratio of the electronic-like band to quinone ring structure (Ie-i/Iquin) value increased first and then decreased with PANI content increasing ,which meant that the conductivity of PANI in the composite has the best value ratio of 0.26.Intensity ratio of Quinone structure to benzene peak (Iquin / Ibenz) decreased following PANI content increasing, which meant Quinones structure declined, caused by the interaction between PANI and C; In PANI/MWNT. The relation between matrix and modifier is conjugate between carbon and Quinone or benzene structure in PANI. /e-1/Iquinvalue increased first and then decreased with PANI content increasing ,which meant that the conductivity of PANI in the composite has a best value ratio of 0.54,which due to orientation of polymer chain along the surface of MWNT.XRD showed that with the content of PANI in the composite gradually increasing, the characteristic peaks of PANI gradually clearly revealed, but the carbon(002) peak intensity weakened, which presented that carbon nanotubes are coated by PANI. At the aspect of the catalysts, we prepared the catalysts(Pt/PANI/C and Pt/PANI/MWNT) by depositing platinum on the composite carriers using chemical redox method .SEM, TEM, XRD and FT-IR test the structure,which explorated the interaction between Pt and carriers,including the impact of particle size and distribution.For Pt/PANI/C, SEM and TEM tests showed that compared with pure carbon black, PANI/C composite carrier can not only supported Pt particles efficiently, but also dispersed Pt particles uniformly with a narrow particle size distribution and the average size of about 7 run For Pt/PANI/MWNT, SEM and TEM showed that in Pt/MWNT, the Pt particles presented in large clusters (40nm) and serious implications between clusters because of bad attachment and dispersion of metal particles.The exist of PANI greatly improve the dispersion of Pt particles, and the ratio of PANI/MWNT 0.54 showed the best form .Small parts are the small clusters(about 10 nm),and more for the single particle size distribution (about 4 nm). XRD showed that the size of Pt in Pt/MWNT is the largest, and with the content of PANI increasing, it became smaller, until 0.54 it showed the smallest size,which is attributed to the different surface structure and morphology of PANI/ MWNT composites. Through the quantitative calculation of the relative content of crystal face Pt(lll), different PANI/C ratio showed similar content, but all significantly increased compared to Pt /C; The ratio 0.54 of PANI/MWNT of the catalysts showed relatively maximum content of Pt(lll),which meant that the surface morphology of PANI/MWNT carriers have greater impact to Pt dispersion compared to PANI/C.In order to investigate the relations between metal particles and the carriers more thoroughly, this paper first test the catalyst by FT-IR. By comparing with the characteristic absorption peak from mutual catalysts and the corresponding carrier ,which proved that there existed interaction between imino groups of PANI and Pt so that the structure of PANI are stable.2. Property of the catalystsBy scanning the PANI/C composite and the catalyst in sulfuric acid medium with multi-ring cyclic voltammetry (CV), The thesis suggested there existed synergy between PANI and Pt particles.which primarily embodied in;(1)The orbit overlap betweenπelectronic track of PANI -imino group and Pt makes PANI more stable in the state; (2)In the potential scanning process, Pt took oxidation reaction prio to PANI and gave PANI electronics, inhibiting its oxidative degradation, so that the catalyst system can exists in the reaction medium steadily; (3) After depositing Pt, the role (1) increased the oxidation state of PANI structure, and reduced the reduction state ,leading to the electrode reaction not as strong as before,which mainly embodied in the decreasing oxidation peak current density from semi-oxidation state to the per-oxidation state.This thesis compared the properties of catalysts towards methanol electro-catalytic oxidation. Through the peak current density, peak potential and the onset oxidation potential it proved that PANI/C 0.12 made the catalytic activity relatively the best.We compared the attenuation Performance of Pt/nano-carbon and Pt/PANI/nano-carbon by scanning the electrodes in methanol solution for 200 Circles .At the end of the scanning, the current density of Pt/C decreased by 60%,corresponding Pt/PANI/C only dropped 20%, which proved resistant to poisoning of the latter is 3 times stronger than the former. The PANI/C composite must have some relationship with Pt metal to prevent the degradation of PANI and enhance the catalytic activity of Pt.By comparing the CV chart of Different carriers and catalysts with different PANI/MWNT ratio in sulfuric acid and methanol solution CV, it showed that methanol can hinder the redox process of PANI, which actuate the adsorb of methanol molecules in turn, inclining the next step oxidation process. The PANI/MWNT ratio of 0.54 showed the relatively highest catalytic ability for methanol electro-catalytic oxidation .The Chronoamperogram measurements presented the superiority of the ability of catalysis and CO anti-poisoning for the Pt/PANI/MWNT comparing to Pt/MWNT. Last,but not least,the CV attenuation Performance of the catalysts showed that besides the superiority of the ability of catalysis and CO anti-poisoning comparing to Pt/MWNT, the Pt/PANI/MWNT was better than the Pt/PANI/C.