Fuel cells membrane stability

Fuel cell membranes are close to optimization with PFSA materials. These materials give excellent performance when fully humidified and have adequate oxidative stability. These materials limit the temperature of operation of the FC to <100°C and have unacceptably high methanol crossover for direct methanol... 

Kim HJ, Litt MH, Shin EM, Nam SY. Hydrolytic stability of sulfonic acid-containing polyimides for fuel cell membranes. Macromol Res 2004 12 545-52. 

Alkaline Membrane Fuel Cells, Membranes, Fig. 7 Anion exchange membrane ex situ stability measurements, (a) Conductivity versus time [26] (b) ion exchange capacity (lEC) versus time [27]... 

The PA-doped /m-PBI fuel cell membrane maintains thermal and physical stability while operating at high temperature. To illuminate the fundamental differences in polymer film architecture, polymers with similar physical characteristics were prepared by the conventional PPA Process (Table 13.1). Even though the ratio of phosphoric acid-to-polymer repeat unit (PA/PRU) achieved by both processes were nearly identical, the PPA Process produces membranes with much higher proton diffusion coefficients and conductivities. The higher protmi diffusion coefficients of membranes produced by the PPA... 

As electrochemical reaction sites, CLs play an extremely important rote in the performance of fuel cell stacks. A CL mainly consists of catalyst, support and binder. The CL is usually coated on the surface of the GDL. Another method has the CL directly applied to the membrane (catalyst coated membrane, CCM). The selection of the components, the proper ratios of those components, the structure of the formed CL and the formation method of the CL are critical factors in the performance of a fuel cell. The stability of the fuel cell performance is directly related to the stabilities of the catalyst, binder and support in flie CL. Degradation of catalytic activity would be due to the agglomeration of the eatalyst particles and their detachment from the support, the degradation of the binder, and the oxidation and corrosion of the support, particularly at the cathode. Further improvement in CL performance is possible. The basic technical considerations include how to maximize the three-phase interface of the CL, how to stabilize the metal particles on the support, and how to reduce the degradation of the components in the CL. 

To compare different polymers with respect to their chemical stability, the Fenton test is widely applied in fuel cell membrane research. In these tests, membrane samples are immersed in hydrogen peroxide solution containing a small amount of Fe " ", e.g., iron(lI)sulfate. In the presence of the metal ion, the decomposition of hydrogen peroxide is accelerated. The ongoing reactions are very complex, and several reactive intermediates are formed. Just as an example and demonstrating the catalytic nature, the following partial reactions of the so-called Haber-Weiss mechanism are highlighted, as shown in (6.28)-(6.31) [49, 50]. 

Gubler L, Koppenol WH (2012) Kinetic simulation of the chemical stabilization mechanism in fuel cell membranes using cerium and manganese redox couples. J Electrochem Soc 159 B211-B218... 

In addition to these two main reactions, there are some other processes having an impact on the electrode behavior. The surface mobility of adsorbed species in the catalytic layer is relevant to analyze the performance and degradation of the fuel cell membrane-electrode assembly. This study is not an easy task and, therefore, these phenomena have been scarcely explored. The diffusion of hydrogen and oxygen adsorbed species is particularly relevant for the performance and stability of PEMFC electrodes. 

Among fluorinated polymers, PTFE is the least polymer used for preparation of radiation-grafted membranes despite its extraordinary chemical, thermal, and mechanical stabilities. This is due to PTFE s extreme sensitivity to high-energy radiation, which produces chain scission with a very small irradiation dose [87], Nevertheless, studies on preparation of fuel cell membranes based on PTFE films were reported in literature [27]. 

---