Perfluoro‐ethylene‐1,2‐bis‐phosphonic Acid Fuel Cell Electrolyte

Abstract

Concentrated aqueous perfluoroethylene-1,2-bis-phosphonic acid, (OH)2OPCF2CF2PO(OH)2, has been investigated as an alternative to phosphoric acid as the electrolyte in the H2/02 acid fuel cell. Phosphoric and bis-phosphonic acid solutions were equilibrated with pure 02 (P = 1 atm) and were used in (i) chronoamperometry experiments performed with a Pt microelectrode to estimate the °2 diffusion coefficient, D, and solubility, C, and (ii) 02 electroreduction polarization studies done with a gas-fed Teflon-bonded carbon electrode with a high surface area Pt catalyst in a microfuel cell. At 22°C in 85% bis-phosphonic acid, C was found to be 3.4 0.3 X iO mol/liter and D was 5.0 0.5 X i0 cm2/s as compared with C = 2.8 0.3 X 10 mol/liter and D = 1.2 0.1 X 10-6 cm2/s in 85% phosphoric acid at T = 22°C. The overpotential for 02 reduction on the microfuel cell cathode was smaller in 85% bis-phosphonic acid than in 85% phosphoric acid for current densities up to 200 mA/cm2 at 100°C. This indicates that the oxygen electroreduction kinetics on Pt increased when phosphoric acid was replaced with the perfluorinated bis-phosphonic acid. At higher current densities ( 200 mA/cm2) where mass transport may influence cathode performance, the performance with bis-phosphonic acid was not as good as with phosphoric acid at 100°C, which is consistent with the higher viscosity and lower D found for bis-phosphonic acid relative to phosphoric acid at 22°C. As the temperature was raised from 100 to 200°C, the cathode performance improved with the bis-phosphonic acid electrolyte. The enhanced 02 reduction kinetics with the bis-phosphonic acid persisted in the fuel cell environment at temperatures up to 200°C for 500 h which demonstrated a major improvement in stability for a high performance perfluorinated fuel cell electrolyte used at higher temperatures such as 200°C.

Design and Synthesis of Cross-Linked Copolymer Membranes Based on Poly(benzoxazine) and Polybenzimidazole and Their Application to an Electrolyte Membrane for a High-Temperature PEM Fuel Cell

“…It was also reported that the addition of perfluorinated compounds increased the solubility and diffusivity of oxygen in phosphoric acid and improved the oxygen reduction kinetics in the cathode [123]. Alternative fluorocarbon acid electrolytes were also used as a replacement for phosphoric acid in an attempt to improve the oxygen reduction rates of Pt [124].…”

“…For the fuel cell that used the phosphoric-acid-doped PBI electrolyte, the amount of PBI in the catalyst layer was found to affect the cell performance [124]. This suggests that the PBI in the catalyst layer absorbed phosphoric acid and provided a path for protons.…”

Arylphosphonic Acid‐Functionalized Polyelectrolytes as Fuel Cell Membrane Material

“…Compared to sulfonic and carboxylic acids, the phosphonic acid group is of intermediate acidity and has been intensely discussed as an alternative protogenic moiety 4, 71–76. By the rise of model compounds' melting and boiling points in the order sulfonic < carboxylic < phosphonic acid, data in Table 1 indicates increasing degrees of interaction by polar and/or hydrogen bonding in the series.…”

“…Perfluorinated alkylphosphonic polyelectrolytes have been produced from various phosphonated perfluorovinylethers,69, 72, 82 as well as from trifluorostyrene phosphonate 83. To obtain suitable film properties, copolymerization with various unfunctionalized perfluorinated monomers was usually required, as is shown in Scheme .…”

Catalyst, Membrane, Free Electrolyte Challenges, and Pathways to Resolutions in High Temperature Polymer Electrolyte Membrane Fuel Cells

“…Kanamura et al investigated the use of perfluoro-ethylene-1,2-bis-phosphonic acid [138], where 85 wt % perfluoro-ethylene-1,2-bis-phosphonic acid and phosphoric acid were tested with a RHE reference electrode and a platinum foil counter electrode. The resulting CV measurements were performed at 22 • C and showed strong hydrogen adsorption peaks on platinum with the Perfluoroethylene-1,2-bis-phosphonic acid versus the phosphoric acid which indicated the Perfluoroethylene-1,2-bis-phosphonic acid was not strongly adsorbing.…”