G-PSSA membranes

T. Lehtinen, G. Sunholm and F. Sundholm, Effect of cross-linking on the physicochemical properties of proton conducting PVDF-g-PSSA membranes, J. Appl. Electrochem., 1999, 29, 677-683 P. Vie, M. Paronen, M. Stromgard, E. Rauhala and... 

Values of proton conductivity of ETEE-g-PSSA, Nafion , PTFSSA, and BPSH membranes are strongly dependent on EW (Fig. 14a). The conductivity of Nafion and PTFSSA membranes maximizes at intermediate EWs, while the conductivity of ETFE-g-PSSA and BPSH membranes increases with decreasing EW. ETFE-g-PSSA membranes possess an exceptionally high conductivity. Compared to ETFE-g-PSSA membranes, a moderate conductivity can be achieved for Nafion , PTFSSA, and BPSH membranes by adjusting the EW of the membrane. However, based on the conductivity-EW relationship for SSEBS membranes, the maximum conductivity obtained is only 0.05 S cm and this is much lower than that of other membranes. 

For Nation membranes, a linear relationship between conductivity and ionic concentration is reahzed. The [H ] of the ETFE-g-PSSA membranes is comparatively larger than those of PTFSSA and SSEBS membranes, and similar to Nation . However, the water content and A. for ETFE-g-PSSA mem-... 

Proton diffusion coefficients for ETFE-g-PSSA membranes (Scheme 2e) have been calculated and compared to those of Nafion 117 (Fig. 27) [189] as well as PTFSSA (Scheme 2h) [190]. Fully hydrated ETFE-g-PSSA and PTFSSA membranes exhibit much higher proton diffusion coefficients than hydrated Nafion 117 due to their high water content. This is in agreement with the higher conductivities observed for fully hydrated ETFE-g-PSSA and, in general, PTFSSA membranes (Fig. 14). However, when proton diffusion coefficients are compared where the three polymer series overlap (e.g., Xy = 0.1-... 

FIGURE12.11 Current-voltage characteristics and power density curves of a PEM fuel ceU with PVDF-g-PSSA membranes having various G%. 

In their efforts to use various fluoropolymer films to develop PCMs, Scherer and co-workers [51] prepared PVDF-g-PSSA membranes in comparison with their counterparts based on ETFE films. PVDF films were activated from y-radiation (dose of 20 kGy at dose rate of 5.9 kGy h ) at room temperature in air and grafting of styrene with peroxidation method interestingly occurred at 60°C. The influence of the base polymer properties on the grafting behavior was addressed [52], Sulfonation of the grafted films conducted with chlorosulfonic acid/dichloromethane mixture at room temperature. The PEMFC performance of PVDF-based membranes was found to be inferior to their ETFE-based counterparts [52],... 

Scott et al. [56] tested radiation-grafted manbranes in DMFC. PVDF-g-PSSA membranes showed superior performance to Nafion under identical conditions at high current density in addition to lower methanol diffusion coefficient by an ordCT of magnitude. However, such membranes suffered performance deterioration after few hundreds of hours due to poor MEA interfacing. 

Lappan et al. [84] reported preparation of new FEP-g-PSSA membranes by radiation-induced grafting of styrene onto cross-linked FEP film using the preirradiation method and subsequent sulfonation. The FEP films were cross-linked by irradiation with EB at molten state (290°C). However, the properties of such membranes have not been reported. A summary of various studies on radiation-grafted PCMs manbranes based on FEP films and their basic properties is presented in Table 5.3. 

Scott et al. [56] tested the performance of radiation-grafted ElEE-g-PSSA membranes in comparison with Nafion in DMEC (90°C, 2M MeOH, and air). The ETFE-g-PSSA membranes showed comparable performance values with Nafion 117, especially with low current densities. 

Hatanaka et al. [92] prepared and tested the performance of ETFE-g-PSSA membranes in DMFC. These membranes were prepared by preirradiation of ETFE film (120 am) from y-radiation followed by styrene grafting and subsequent sulfonation. The membranes with degrees of grafting exceeding 30% displayed better transport properties, i.e., higher ionic conductivity and lower methanol permeation, compared with Nafion membranes. However, the PEM fuel cell performance of these membranes was found to be inferior to that of Nafion. The authors attributed such behavior to the poor bonding of the electrodes to the membrane surface in the MEA. 

Similar ElFE-g-PSSA membranes were prepared by Arico et al. [93] with electron irradiation, subsequent grafting, cross-linking, and sulfonation. The obtained man-brane samples were of commercial size. The membranes showed good conductivity and low methanol crossover at a thickness of around 150 pm. MEA assembUes based on these manbranes showed DMFC performance and cell resistance values comparable to Nafion 117 (210 pm). Stable electrochemical performance was recorded during 1 month of cycled operation at a temperature of 110°C. 

Earlier Nezu et al. [128] reported a PEMFC test with radiation grafted PFA-g-PSSA membranes in comparison with counterparts based on PTFE and FEP films. However, no details on the preparation conditions and properties of these membranes were released. 

Results from a series of degradation tests on grafted polystyrene sulfonic acid (g-PSSA) membranes have shown that thinner membranes have higher degradation rates than thicker ones (Gubler et al. 2005). Divinylbenzene cross-linked membranes have higher durability than non-cross-linked membranes owing to their lower gas crossover rate. 

NMR was used to characterize PTFE-g-PSSA membranes (Assink et al. 1991). The experiments were conducted at 50.16 MHz using dioxane (0.3%) as an internal standard set at 67.4ppm. Resonance peaks at 169,173, and 178 ppm were assigned to carboxylic acid or ester functional groups. Peaks in the region of 50-80 ppm correspond to carbons next to an alcohol or ether, while peaks in the 15-35-ppm range represent various aliphatic carbons. 

Detailed discussions on the membrane chemical degradation mechanisms will first be divided into three main categories hydrocarbon membranes, g-PSSA membranes, and PFSA membranes. General degradation pathways and correlations between different types of membranes will be discussed at the end of this section. 

G. Guo, R. lie, S. An, Performance of the self-breathing air direct methanol fuel cell with modified poly (vinylidene fluoride) grafted onto a blended polystyrene sulfonated acid (m-PVDF-g-PSSA) membranes, Adv. Mater. Res., 152-153 (2011) 149-153. 

---