Experimental investigation of changes in membranes morphology and microstructure under freeze-thaw cycles for PEMFCs : Experimental investigation of changes in membranes morphology and microstructure under freeze-thaw cycles for PEMFCs

• Main Authors: Spasov, D.D., Ivanova, N.A., Pushkarev, A.S., Butrim, S.I., Seregina, E.A., Fateev, V.N.
• Format: Conference Object
• Language: English
• Published: Институт физики твердого тела РАН 2019
• Subjects: Arctic
• Online Access: https://dx.doi.org/10.26201/issp.2019/fc.5; http://www.issp.ac.ru/ebooks/conf/FuelCell_2019.pdf#page=280

For a number of fuel cells applications (including the power supply of the Arctic territories, unmanned aerial vehicles, etc.), there is an urgent need to ensure their launch and operation at negative temperatures. Studies of the operation of FC at low temperatures started long enough. A certain practical success has been achieved, namely, the launch of solid polymer fuel cells in the temperature range -20 °C - -15 °C [1-5] is reported. However, the optimal solution to the described problem has not been found, which retains the relevance of modern research in this area [6,7]. In this paper, we studied the effect of temperature cycling from the room (about 20 ОС) to low (-35 or -80 ОС) on the physicochemical and operational characteristics of the membrane. We investigated the membrane brand Nafion 212 50 µ thick. The membranes treated with three different methods: D – dry, untreated membrane, M – treated by the standard method membrane without liquid water and L – treated according to the standard method membrane with traces of a liquid DI water. The standard procedure of membrane treatment assumed the transfer of the membrane to the H+-form during boiling in HNO3 aqua solution. Membranes were exposed to low temperatures by cycling from -35 (-80) to 20 OC, and the duration of each stage was at least 2 hours (see figure 1). After a certain number of cycles, the membranes were ex-situ examined. Fig. 1. Freeze-thaw cycles method scheme. Experimental studies. ESEM was performed. The specific volume resistance and moisture capacity of the membranes were also investigated. The membranes were also tested as part of a membrane-electrode bloke and 40Pt/Vulcan XC-72 (10 wt.% of Teflon) was used as a catalyst for the anode and cathode with a deposition density of 1.05 mg/cm2. The measurements of the polarization curve versus current density were performed using a Solartron 1285 (Solartron Analytical, USA) potentiostat in the potential range from 0.9 to 0.1 V in the potentiodynamic mode. The operating temperature of the cell is 35-50 °C. Two U-I curves of each cell were taken sequentially, first using oxygen and hydrogen, and then hydrogen and air as operating gases. ESEM images for D and M membranes were obtained (see figure 2). Visible differences in membranes morphology are not observed on these images. Fig. 2. ESEM images of D (left) and M (right) membranes. Scale bar 20 µ. In figure 3, the curves of changes in the specific volume resistance for various membranes after 5, 15, and 30 cycles are freeze-thaw plotted. Visible dependence is observed only for dry untreated membrane. Such an effect is observed for both resistivity and water capacity. Water capacity of all investigated membranes was near 20 wt.%. Fig. 3. The specific volume resistance versus number of freeze-thaw cycles (the numbers in the membrane name indicate freezing temperature). In the FC cell, M and L membranes are used, for which influence of freeze-thaw cycles for morphology and properties is absent. For these membranes, U–I curves in the 1 cm2 experimental FC with GDL — Sigracet 39 BC were obtained. The U-I curves are shown in figure 4. Fig. 4. U-I curves for 1 cm2 FC with membranes after 30 freeze-thaw cycles. According to the results of research, it can be concluded that the working parameters of the cell with the membranes subjected to freezing are improved in comparison with the initial characteristics of FC. The reported study was funded by RFBR according to the research project №18-29-23030. Studies performed in NRC “Kurchatov institute” were supported by project no. 1390. References [1] F. Jiang, C-Y. Wang, “Potentiostatic start-up of PEMFCs from subzero temperatures.”, J Electrochem Soc, vol.155, pp.B743–51 (2008). [2] M. Khandelwal, S. Lee, M.M. Mench, “One-dimensional thermal model of cold-start in a polymer electrolyte fuel cell stack.”, J Power Sources, vol.172, pp.816–30 (2007). [3] R. Lin, Y. Weng, X. Lin, F. Xiong, “Rapid cold start of proton exchange membrane fuel cells by the printed circuit board technology.”, Int J Hydrogen Energy, vol.39, N183, pp. 69–78 (2014). [4] Q. Guo, Y. Luo, K. Jiao, “Modeling of assisted cold start processes with anode catalytic hydrogen-oxygen reaction in proton exchange membrane fuel cell.”, Int J Hydrogen Energy, vol.38, pp.1004–15 (2013). [5] Y. Tabe, M. Saito, K. Fukui, T. Chikahisa, “Cold start characteristics and freezing mechanism dependence on start-up temperature in a polymer electrolyte membrane fuel cell.”, J. Power Sources, vol.208, pp.366-373 (2012). [6] Z. Wan, H. Chang, Sh. Shu, Y. Wang, H. Tang, “A Review on Cold Start of Proton Exchange Membrane Fuel Cells.”, Energies, vol.7, pp.3179-3203 (2014). [7] L. Yao, J. Peng, J-b. Zhang, Y-j. Zhang, “Numerical investigation of cold-start behavior of polymer electrolyte fuel cells in the presence of super-cooled water.”, Int J of Hydrogen Energy, vol.43, N32, pp. 15505-15520 (2018).