Preparation and Evaluation of Nanocomposite Membranes Based on Sulfonated Graphene Oxide and Carbon Nanotube for Aluminum Air Batteries

The procedure of membrane synthesis and evaluation plays an important role in development of new energy related technologies such as fuel cells, batteries and electrolyzer. The main challenge of membrane technology is the synthesis of high efficient, environmental friendly and cost effective membranes. In this work, a series of proton exchange membranes based on multi-functionalized graphene oxide (GO) and multi walled carbon nanotube (MWCNT) were synthesized via a solution casting procedure. The structure and morphology of the samples were investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and optical polarizing microscopy. Finally, the synthesized membranes were evaluated for proton conductivity from the point of measured current versus time at a constant potential in a homemade aluminum air battery cell setup and compared with the commercial nafion 112 membrane. For the synthesis of membranes, at first GO was synthesized through modified hummer method [1], MWCNT purchased from US research nanomaterials Inc. (OD: 20-30 nm) and purified via reflux treatment in HCl: HNO3 solution at 90 ◦C for 30 min, Then they were sulfonated via chlorosulfonic acid [2] and labeled as GO-SO3H and MWCNT-SO3H respectively. The membranes were prepared by casting the polymer solution of polyacrylonitrile/dimethylformamide With GO, GO-SO3H and MWCNT-SO3H to get modified membranes with the labels of GO-AN, GO-SO3H-AN and MWCNT-SO3H-AN. Fig. 1 shows the FT-IR spectra of GO, GO-SO3H and MWCNT-SO3H. As it can be seen in the figure, all of the characteristic peaks of C-O, C=C, C=O and C-OH are obvious in all samples spectra. But GO-SO3H and MWCNT-SO3H spectra showed the additional O=S=O stretching vibration, -SO3- symmetrical stretching vibration and S-OH stretching vibration which can enhance the proton conductivity of membrane. 119 Figure 6. FT-IR spectra of GO, of GO-SO3H and MWCNT-SO3H Fig. 2 shows the optical polarizing microscopy of GO-SO3H. It confirms the transparity and presence of sulfonated GO in the nanocomposite membrane. The average currents of GO-SO3HAN, MWCNT-SO3H-AN and GO-AN were 705, 653 and 608 mA at 2.3 V whereas the measured current for nafion 112 was 1200 mA at this voltage. It appears that of GO-SO3H-AN and MWCNTSO3H- AN nanocomposite membranes can be good candidates for future battery applications Figure 7. Typical optical polarizing microscopy of GO-SO3H