POLYMER NANOHYBRIDS FOR PROTON EXCHANGE MEMBRANE IN FUEL CELLS

Abstract

Proton exchange membrane fuel cell (PEMFC) a staging change for engineers and researchers mostly mechanical engineers due to its great potential and bright future over conventional battery as well as combustion engine. It is highly capable to revolutionize the automobile industry concept of power supply to the vehicles. Strategically strong point of PEMFC is zero carbon emission with cost effective assemblies. Reliability of fuel cell is proven since 1980s, but not used for daily electricity consumption. Within the next one or two dictates there is a highly likely possibility of replacing the conventional combustion engine by the electric powered motor all over the world. Some future aimed automobiles are already in the market and some will run in near future. To power the electric motor PEMFC is the strongest competitor of conventional batteries. PEMFC has some insightful advantages over conventional power system i.e. fuel loading into the fuel tank can save several hours of recharging time of the battery, Hydrogen (H2, is the proton donating element for PEMFC, 236 times higher per kilogram for H2, energy density and light weight in nature) has more specific energy (40,000 Wh/kg) than conventional lithium-ion battery (it has 278 Wh/kg at best) hydro carbon fuel, water is the main and free source of H2 and can be split by solar energy on site and many more. Mercedes-Benz fuel cell car and Toyota hybrid fuel cell car are already creating a big challenge to Tesla and other battery powered car manufacturer world-wide, due to its great potential and bright future over conventional battery. PEMFCs have the pronounced potential to convert every house as a green power station in coming future. Tremendous amount of recent effort and research are focused to elevate the working temperature of PEMFC known as High Temperature PEMFC or HT-PEMFC, which working temperature should be more or equal to 100 ºC. Nafion (perfluorosulfonated ionomer) is the most commercialized polymer, used as polymer electrolyte membrane (PEM) in PEMFC. Nafion PEMs are not popular as HT-PEM due to its lower working temperature (is only up to 80 ºC) and water molecule retention is required for proton (H+) migration through PEMs. In this research, the proton exchange membrane (PEM) composed of sulfonated poly(ether ether ketone) (SPEEK) as a matrix material and reduced graphene oxides nanoribbons (rGONR) wrapped titanium dioxide (TiO2) microspheres as filler is fabricated using simple solution casting method. The incorporation of the of rGONR (optimised amount) wrapped TiO2 (rGONR@TiO2) nanofiller, acts as a novel self-humidifying/water trapping nanoshell and regulates the presence of (-SO3-)n ionic clusters in SPEEK matrix to build a better network without losing the motion of protons. The network formation dramatically stimulated the proton transport of the SPEEK/rGONR@TiO2 (SPTC) nanohybrid PEM and improved it up to 188% (0.62 S cm-1 for SPEEK to 1.79 S cm-1 for SPTC) at 100 °C. The activation energy (Ea) and diffusion coefficient (Dσ) for SPTC membrane are found to be 9.15 kJ mol-1 and 4.92×10-8 m2 s-1, respectively, which is in an excellent agreement to ensure better proton conductivity and lower ionic resistance. Furthermore, Sulfonated poly(ether ether ketone) –MO2 (M = Zr, Si) –carbon nanotubes (CNTs) nanocomposite membranes in the proton exchange membrane fuel cells (PEMFCs) were synthesized to enhance the proton mobility and water maintenance at elevated temperature (100 °C). The proton exchange membranes (PEMs) were synthesized by simple solution casting method, and the drying process (using controlled infrared (IR) lamp heating and air draft oven at adjusted temperature ramp) of the membranes were optimized to cast uniform (uniform thickness and homogeneous nanoparticle distribution in the PEMs) membranes to compare their results at different temperature. It was observed that the synergic effect of SiO2@CNT and ZrO2@CNT as nanofiller dramatically enhanced the proton conductivity, thermal stability, chemical reliability, and mechanical strength of the PEMs. Form this study, it was observed that between 40 to 60 °C, vehicular mechanism plays a key role, and between 80 to 100 °C Grotthuss mechanism plays a vital role in proton migration. Moreover, the combined proton transfer effect was observed in case of SPEEK/SiO2@CNT/ZrO2@CNT membrane, which exhibited 2 times better conductivity at 40 and 60 °C, 5 times better conductivity at 80 °C and 8 times better at 100 °C than the commercial Nafion 212 (N212) membrane under same setup and condition.