New composite PEM for high temperature fuel cells (abstract)

New composite PEM for high temperature fuel cells

M. E. Cordova; A. E. Sleczka; E.M. Kelder; S. J. Picken

TU Delft, ChemE, Nanostructured Materials Julianalaan 136 2628 BL, Delft, The Netherlands

The first commercial use of fuel cells was in NASA space programs to generate power for probes, satellites and space capsules. Since then, fuel cells have been used in many other applications. Fuel cells are used for primary and backup power for commercial, industrial and residential buildings and in remote or inaccessible areas. They are used to power fuel cell vehicles, including automobiles, buses, forklifts, airplanes, boats, motorcycles and submarines.[1]

One of the biggest challenges for fuel cells is

to work over 100 °C because their

efficiency increases with temperature while at the same time the water needed for the proton conduction in the membrane is gone. The aim of this work is, using Sulphonated Poly (Ether Ether Ketone) (SPEEK) together with inorganic fillers that contain water ì.e. hydrate salts, to try to develop a membrane able to fill these new requirements.

EXPERIMENTAL SPEEK Synthesis

Commercial PEEK (Vitrex 450 PF) with a Mw: 39200 g r/mol [2] was sulphonated in a reactor (95/5 v/wt.) with sulphuric acid (98% sigma-aldrich) at 55°C for 5 hours and 75 hours (sulphonation degree [SD] 60% and 100% respectively obtain using back titration [3]). Before the reaction, the PEEK was dissolve in the sulphuric acid completely. The solution was then washed with demineralized water until the pH was neutral. [3] The modified polymer was dried in a vacuum oven for 1 week at 120°C.

Membrane Preparation

The membranes were made with SPEEK5h and SPEEK75h in 55% wt. and a hydrated salt (FeSO4+7H2O, CuSO4 5H2O and NiSO4 6H2O) with 45% wt. All the components were grinded to a 45μm size. The polymer was dissolve in N,N-Dimethylacetamide (DMAc) at 120°C with a continuous stirring, when the solution was homogeneous the salt was added. When a homogeneous solution was obtained it was casted in a PTFE plate and the solvent was evaporated in a vacuum oven at 120°C.

Equipment

Differential Scanning Calorimetry (DSC) and TGA were made under an inert atmosphere (pure nitrogen). The DSC was a Perkin Elmer DSC 7 and the TGA was Perkin Elmer TGA 7.

RESULTS AND DISCUSSION

In Figure 1 the TGA measurements are presented. The polymer obtained after the sulfonation is stable over 200°C, at 300°C a partial degradation of the polymer occurred as a consequence of the released of the sulphonated group and finally the degradation of the carbon base groups occurred over 500°C. [4]

The main objective of used of the salt in the membrane is to keep the water inside the membrane

even when the temperature goes over 100°C. In Figure 2 it can be seen that in the DSC results that the water goes out at higher temperatures keeping the membrane available for conduction. Also, the salts are able to couple with the sulphonated groups in the SPEEK creating a path for the protons through the membrane. 100 200 300 400 500 600 50 60 70 80 90 100 110 SPEEK 75h SPEEK 5h

Weight (%)

Temperature (°C)

Figure 1. TGA results obtained before and after the

polymer sulphonation under an inert atmosphere.

30 60 90 120 150 180 NiSO4+6H2O CuSO4+5H2O

Heat Flow (mW)

Temperature (°C)

Figure 2. first heating DSC scans at 10°C/min of

different hydrated salts.

DSC, TGA, Impedances Spectroscopy, Polarization Curves at different temperatures will be showed in the congress along with a comparison of the results with the performances of Nafion membranes.

REFERENCES

1. S. Basu, Recent Trends in Fuel Cell Science and Technology, Springer, New Delhi (2007).

2. M. Di Vona, D. Marani, C. D’Ottavi, M. Trombetta, E. Traversa, I. Beurroies, Ph. Knauth and S. Licoccia, Chem. Mater., 18; 69 (2006). 3. R. Huang, P. Shao, C. Burns and X. Feng, J. App.

Polym. Sci., 82, 2651 (2001).

4. S. Zaidi, S. Mikhailenko, G. Robertson, M. Guiver and S. Kaliaguine, J. Membrane Sci., 173,17 (2000).