Preparation Of Ion-exchange Membranes Doped By Dyes And Their Application Performances For Fuel Cells

Currently, low-temperature fuel cells have been widely paid attention and they fall into two categories:proton exchange membrane ?PEM? fuel cells and anion exchange membrane ?AEM? fuel cells. The proton exchange membrane fuel cell has many advantages such as quick start at room temperature, excellent ionic conductivity, and light weight and small volume. However, the synthesis of most of PEM fuel cells has some difficulties because of high cost metals platinum catalysts, which limit PEM fuel cells'widespread application. Compared with PEM fuel cells, the AEM fuel cells can offer many advantages, such as good chemical dynamics, less dependence on the noble metal catalyst. However, its electro chemical performances, especially ionic conductivity still have a big disparity with those of PEMs, therefore new membranes for low temperature fuel cells need to be urgently exploited and utilized.Reactive dye is a kind of ionic dyestuffs with reactive groups, and has many strong electron acceptors and electron donors in its chemical structure. It also has highly delocalized conjugated system which can transfer electrons effectively, good compatibility with polymer film, ionic properties and can conduct H+ or OH- effectively. In this paper, reactive dyes with different chemical structure as conductive components are introduced into membranes for the first time by doping and grafting means for fuel cells, which can be kept in the membranes to transfer ions. The chemical structure, physical morphology, conductive performances and applied properties of the prepared ionic exchange membranes have been studied systematically, and the main points are summarized as follows:?1? A new type of proton exchange membranes based on poly?vinyl alcohol? ?PVA? and KE reactive dyes ?KE-4BD? had been prepared through the doping, blending and glutaraldehyde ?GA? crosslinking technologies. Aldolization between GA and PVA can be proved by FTIR and XPS. PVA/KE-4BD membranes show the high oxidative and thermal stability. The proton conductivity of the PVA/KE-4BD membrane ?1:0.5, in mass? can reach 0.109S cm^-1 at ambient temperature and affords a power density of 83.9mW cm^-2 at 210.4mA cm^-2 with open-circuit voltage ?OCV? of 810.8mV in a single H2/O2 fuel cell. The generating capacity is close to that of Nafion???212 membrane under the same conditions, indicating that the PVA/KE-4BD membrane has the excellent applied performance.A cationic reactive dye LCRD was blended with chitosan solution, followed by the GA crosslinking treatment, to synthesize a novel dye-doped anion-exchange membrane. Schiff base reaction between CTS and GA can be proved by FTIR and XPS. At ambient temperature, the OH-conductivity of the CTS/LCRD membrane ?1:0.5, in mass? reaches 3.18×10-S cm^-1. The membrane also affords a power density of 21.8mW cm 2 at 42.6mA cm 2 in a single H2/O2 fuel cell. In addition, after immersing the membrane in the KOH solution (80?,6mol·L^-1) for 168 hours, the OH- conductivity of the membrane remains 85.5% of that of the original sample, which indicates that the membrane has the certain resistant alkaline stability.?2? Pristine PVA membranes were prepared firstly, then X-type reactive dyes (X^-2R) were used to dye the pristine PVA membranes to fabricate a new type of proton exchange membranes, and the prepared membranes were subsequently treated by the GA solution. The PVA-X^-2R membrane ?45?m? shows excellent mechanical properties. The breaking strength is 40.5Mpa and its breaking elongation is 80.6%.The membrane shows a conductivity of 0.0519 S cm^-1 and affords a power density of 48.9 mW cm^-2 at 127.4 mA cm^-2 and OCV of 893.1 mV at ambient temperature.The cationic reactive dye LCRD was used to dye CTS films and the prepared membrane CTS-LCRD was also treated by the GA solution. The conductivities of the CTS-LCRD membranes are 0.82-4.59×10-3S cm^-1 while the thicknesses of the membranes are from 36?m to at ambient temperature. The breaking strength of the CTS-LCRD membrane ?52?m? is 27.63Mpa and its breaking elongation is 11.3%. Compared to the blended CTS/LCRD membrane, the dyed CTS-LCRD membrane has the comparable conductivity and generating capacity, but has the better mechanical properties and alkaline stability. The membrane also affords a power density of 25.8mW cn^-2 at 42.6mA cm^-2 in a single H2/O2 fuel cell. The adsorption mechanism and adsorption type was analyzed. The results showed that the pseudo second-order rate equation fitted the experimental data well and the adsorption process was controlled by chemical reaction.?3? An anionic polymeric dye XDCTS was blended with PVA to prepare a novel proton exchange membrane and the prepared PVA/XDCTS membrane was also treated by the GA solution. The prepared SEMI-interpenetrating network ?SEMI-IPN? membrane exhibits good thermal stability and mechanical performance, but its conductivity 8.69×10-3 S cm^-1 is relatively low. Compared with the benchmark Nafion and other kinds of PEMs in this paper, there is a considerable gap and the membrane preparation technology needs further improvement.Using PVA as the matrix with an anionic polymeric dye PRDS as conductive components, using MWCNTs as the performance enhancer, a novel proton exchange membrane PVA/PRDS/MWCNTs was prepared, which was subsequently treated by the GA solution. With the addition of MWCNTs, the SEMI-IPN PVA/PRDS/MWCNTs membrane shows higher thermal stability, mechanical properties, and chemical stability than those of the PVA/PRDS membrane. But MWCNTs over a certain dosage will cause conglomeration and has a negative effect on the properties of the membrane. The conductivity of the membrane between 2.91×10-3S cm^-1-9.53×10-3S cm^-1 is lower to those of Nafion and other kinds of PEMs in this paper and needs be further improved.?4? A novel SEMI-IPN anion exchange membrane was prepared by a cationic polymeric dye PRDQA and CTS. The OH- conductivity of CTS/PRDQA membrane ?1:0.5 in mass? can reach 8.17×10-3S cm^-1 at ambient temperature. At a current density of 57.4mA cn^-2, this membrane achieved a power density of 29.1mW cm^-2 with OCV of 991.6mV in a H2/O2 system. The membrane shows good alkaline stability, and its conductivity and water uptake are better than those of the original sample. The mechanical properties of the CTS/PRDQA membranes such as the breaking strength, breaking elongation decrease gradually with the increase of the dyestuff content in the membrane.A novel SEMI-IPN alkaline anion-exchange membrane from poly?vinyl alcohol?/ poly?acrylamide-co-diallyldimethyl ammonium chloride? by incorporating polyethylene glycol as a plasticizer and chemical cross-linking method was successfully prepared. The anionic conductivity is found to be greatly dependent on the content of PEG in the membrane. The conductivities of the membranes increase from 0.565×10-3 S cm^-1 to 1.14 × 10-3 S cm^-1 at room temperature with the increased PEG content. When the PEG is incorporated, the ion transport activation energy decreases from 32 kJ mol^-1 ?PVA/PAMDDAC 1:0.25 by mass? to 25.8 kJ mol^-1 ?PVA/PAMDDAC/PEG 1:0.25:0.25 by mass?. The flexibility of the membrane is improved because of plasticizer effect, which leads to more free room and more active ability of ionic. A maximum power density of 15.9 mW cm^-2 of DMFC with the membrane ?=1:0.25:0.25 by mass? can be reached at 70?.?5? CTS, dye-ionic liquids [QAIM]OH and MWCNTs-OH was blended, GA crosslinking was followed, and a novel alkaline polymeric electrolyte membrane was formed. The results of XRD and FTIR indicate that [QAIM]OH and MWCNT-OH are successfully introduced into the CTS matrix. SEM analysis shows that the roughness within the membrane is increased due to the additive of ionic liquids and carbon nanotubes. The thermal stabilities of both the CTS/[QAIM]OH membrane and the CTS/[QAIM]OH/MWCNTs-OH membrane have become better than that of the pristine CTS film. The tensile strength of the former is comparable to that of the pristine CTS membrane, but the breaking elongation is obviously higher than those of the pristine CTS membrane. The activation energy Ea of the CTS/[QAIM1OH/MWCNTs-OH membrane ?1:0.5/3%? is 11.97 kJ mol, which indicates that both Grotthus and Vehicle mechanism exist during the ionic conductive process. At a current density of 59.9mA cm, this membrane achieves a power density of 31.6mW cm^-2 in a H2/O2 system. Under the condition of middle temperature (100^-140?) with no water, the conductivities of the membranes increase with the increase of temperature and the amount of ionic liquids in the membrane respectively, indicating that the ionic transport behaviors still can be running.