A novel hybrid fuel cell is described using at least one electrode operating at high pH in an effort to use the high conductivity of Nafion and exploit the electrochemical advantages of high-pH operation. The electrochemical behavior of a hybrid anion exchange membrane (AEM)/proton exchange membrane (PEM) junction and corresponding fuel cell are presented. Two AEM/PEM junctions and fuel cells have been evaluated: AEM anode/PEM cathode and PEM anode/AEM cathode. The AEM cathode/PEM membrane configuration causes proton−hydroxide recombination at the membrane junction, resulting in self-hydration of the membrane. The fuel cell performance improves at lower relative humidity. At 65 °C and 0% relative humidity, the hybrid cell operates at steady state whereas the performance of a conventional PEM cell decreases with time due to dry-out.
In this study, the performance of the anionic electrodes in polymer-based alkaline fuel cells is analyzed. Direct alcohol, alkaline fuel cells suffer from a rapid decrease in cell potential at low discharge currents. Several effects are described to account for this drop in cell potential. Quaternary ammonium ions can specifically adsorb on the catalyst surface decreasing the active surface area and lowering the rate of methanol oxidation. In addition, the tethering of the quaternary ammonium cations on the polymer electrolyte inhibits the cation mobility causing a diffuse double layer to be formed. The diffuse double layer electrostatically inhibits the migration of hydroxide to the surface of the electrode which is needed for alcohol oxidation.
The microstructure of perfluorinated sulfonic acid proton-exchange membranes such as Nafion significantly affects their transport properties and performance in a vanadium redox-flow battery (VRB). In this work, Nafion membranes with various equivalent weights ranging from 1000 to 1500 are prepared and the morphology-property-performance relationship is investigated. NMR and small-angle X-ray scattering studies revealed their composition and morphology variances, which lead to major differences in key transport properties related to proton conduction and vanadium-ion permeation. Their performances are further characterized as VRB membranes. On the basis of this understanding, a new perfluorosulfonic acid membrane is designed with optimal pore geometry and thickness, leading to higher ion selectivity and lower cost compared with the widely used Nafion 115. Excellent VRB single-cell performance (89.3% energy efficiency at 50 mA·cm) was achieved along with a stable cyclical capacity over prolonged cycling.
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