12-Silicotungstic Acid Doped Phosphoric Acid Imbibed Polybenzimidazole for Enhanced Protonic Conductivity for High Temperature Fuel Cell Applications

Abstract

12-Silicotungstic acid, a heteropoly acid (HPA) -was incorporated into phosphoric acid (PA) doped polybenzimidazole (PBI) membrane that exhibited strong mechanical stability, excellent proton conductivity, and can be used for high temperature proton exchange membrane fuel cells (PEMFCs). At 160 • C, an electrochemical impedance spectroscopy (EIS) fitting of the fuel cells data showed the membrane electrode assemblies (MEAs) made of PBI/20%HPA/PA had three times lower ohmic resistance (0.057 ± 0.002 Ohm * cm 2 ) as compared to the control reference of PBI/PA (0.160 Ohm * cm 2 ). In addition, the ohmic resistance of the composite MEA remained unchanged while the charge transfer resistance decreased after 313 hours conditioning. Fourier transform infrared spectroscopy (FTIR), magic angle spinning -nuclear magnetic resonance (MAS-NMR), and thermogravimetric analysis (TGA) showed 12-silicotungstic acid inhibits water from escaping the membrane at elevated temperatures and adds more acid sites, providing additional paths for proton transport. Scanning electron microscope (SEM), transmission electron microscopy (TEM), and small angle X-ray scattering (SAXS) were used to confirm the structure and morphology of PBI/20%HPA/PA membrane prior making the MEAs. Fuel cell technologies have the potential to reduce our dependence on fossil fuels and to reduce associated emissions of pollutants as the global population continues to grow. Polymer electrolyte membrane fuel cells (PEMFCs) have the advantage of being fully scalable for stationary power generation than other types of fuel cells. PEMFCs have outstanding power density, rapid start-up, and high efficiency. 1In addition, the operation of PEMFCs is straightforward and does not generate any additional pollutants. Despite several advantages, current PEMFCs are not yet widely used or commercialized, because they remain too expensive, do not have enough durability, and require very pure hydrogen as a fuel.2 At the moment, PEMFCs generally operate below 100• C due to the need to fully humidify commonly used perfluorosulfonic acid electrolytes such as Nafion. At low operating temperatures, a small concentration of CO or SO 2 impurities in the fuel could poison the catalysts and lower the fuel cell performance. Therefore, current PEMFCs require high purity hydrogen that can only be cost-effectively produced from natural gas at this time. Furthermore, the humidification of fuel and oxidant in low temperature PEMFCs requires a complicated humidification system. These technical challenges can be addressed by increasing operating temperatures above 120• C. High temperature operation is a promising way to improve PEMFC performance; it has been shown that higher operating temperatures would increase chemical kinetics at the anode and dramatically enhance the electrode tolerance to fuel impurities, which allows for the use of lower-cost hydrogen.3 In addition, fuel cell operation above 120• C can tolerate up to 1% CO and 10 ppm SO 2 . Operating at elevated temperatures would also provid...

Porous Proton Exchange Membrane with High Stability and Low Hydrogen Permeability Realized by Dense Double Skin Layers Constructed with Amino tris (methylene phosphonic acid)

“…The peaks of these two forms of the p ‐OPBI‐ATMP/PA membrane move toward the low field, and the spectral linewidth narrows, indicating the higher proton mobility, and higher proton conductivity. [ 58,59 ] In addition, the FT‐IR spectrum also shown in Figure 4e demonstrates that hydrogen bonds were present inside the ATMP molecules. Thus, protons were continuously dissociated with increasing temperature, leading to effective proton conductivity (Figure S17, Supporting Information).…”

Water Electrolysis toward Elevated Temperature: Advances, Challenges and Frontiers

“…236 Exceptional durability at elevated temperatures was also attained by composite membranes with PWA-functionalized mesoporous silica (PWA-meso-SiO 2 ) for 2600 h at 200 °C237 and 12silicotungstic acid (SWA) for 700 h at 160 °C. 238 Other materials involving muscovite (Mus), 239 mixed zeolitic imidazolate framework (ZIF-Mix) composed of ZIF-8 (Znbased MOF) and ZIF-67 (Co-based MOF) 240 and ionic-liquidfunctional silica (ILS) 241 have also been utilized to fabricate PBI-based composite membranes for ET-PEMECs, which are collectively presented in Table 11.…”

“…Moreover, the incorporation of solid acid ZrP resulted in an extraordinary proton conductivity of 200 mS·cm –1 at 180 °C, and excellent stability for 730 h at 150 °C was illustrated by composite membranes with 10 wt % α-ZrP nanoparticles . Exceptional durability at elevated temperatures was also attained by composite membranes with PWA-functionalized mesoporous silica (PWA- meso -SiO 2 ) for 2600 h at 200 °C and 12-silicotungstic acid (SWA) for 700 h at 160 °C . Other materials involving muscovite (Mus), mixed zeolitic imidazolate framework (ZIF-Mix) composed of ZIF-8 (Zn-based MOF) and ZIF-67 (Co-based MOF) and ionic-liquid-functional silica (ILS) have also been utilized to fabricate PBI-based composite membranes for ET-PEMECs, which are collectively presented in Table .…”

Advancement in Phosphoric Acid Doped Polybenzimidazole Membrane for High Temperature PEM Fuel Cells: A Review

“…Thus, PBI/CNT composite were prepared and improvement in the mechanical properties are observed for both undoped and doped nanocomposite as the tensile strength and Young's modulus were increased by 32% and 147% respectively. Heteropolyacids (HPAs) such as 12silicotungstic acid, H4SiW12O4.29H2O has successfully incorporated into PBI membrane without using SiO2 as a support [68]. After doping with PA, most of the HPA able to retain in the polymer matrix.…”