[en] Polyaniline/Nafion and polypyrrole/Nafion composite membranes, prepared by chemical polymerization, are studied by infrared and nuclear magnetic resonance spectroscopy, and scanning electron microscopy. Differences in vanadium ion diffusion through the membranes and in the membranes area specific resistance are linked to analytical observations that polyaniline and polypyrrole interact differently with Nafion. Polypyrrole, a weakly basic polymer, binds less strongly to the sulfonic acid groups of the Nafion membrane, and thus the hydrophobic polymer aggregates in the center of the Nafion channel rather than on the hydrophilic side chains of Nafion that contain sulfonic acid groups. This results in a drastically elevated membrane resistance and an only slightly decreased vanadium ion permeation compared to a Nafion membrane. Polyaniline on the other hand is a strongly basic polymer, which forms along the sidewalls of the Nafion pores and on the membrane surface, binding tightly to the sulfonic acid groups of Nafion. This leads to a more effective reduction in vanadium ion transport across the polyaniline/Nafion membranes and the increase in membrane resistance is less severe. The performance of selected polypyrrole/Nafion composite membranes is tested in a static vanadium redox cell. Increased coulombic efficiency, compared to a cell employing Nafion, further confirms the reduced vanadium ion transport through the composite membranes.

[en] The stability of the electrolytes for all-vanadium redox flow battery was investigated with ex-situ heating/cooling treatment and in-situ flow-battery testing methods. The effects of inorganic and organic additives have been studied. The additives containing the ions of potassium, phosphate, and polyphosphate are not suitable stabilizing agents because of their reactions with V(V) ions, forming precipitates of KVSO6 or VOPO4. Of the chemicals studied, polyacrylic acid and its mixture with CH3SO3H are the most promising stabilizing candidates which can stabilize all the four vanadium ions (V2+, V3+, VO2+, and VO2+) in electrolyte solutions up to 1.8 M. However, further effort is needed to obtain a stable electrolyte solution with >1.8 M V5+ at temperatures higher than 40 C.

[en] Through-plane liquid accumulation, distribution and transport inside polymer electrolyte fuel cell (PEFC) components were analyzed as a function of channel wall hydrophobicity with the use of high-resolution neutron imaging. Neutron images were taken with polytetrafluoroethylene (PTFE) coated and uncoated flow channel walls. Anode to cathode liquid distribution was analyzed for each case at low and high current conditions over 20 min of operation. The form and amount of liquid water inside the channels and diffusion media (DM) were compared for hydrophobically coated channels and hydrophilic channels, and a primary liquid transport-flooding mechanism is suggested for each case. The location and value of maximum water storage in DM at low and high current operation were analyzed and slopes of water mass versus distance curve were calculated to compare the significance of capillary liquid flow and phase-change-induced flow within the diffusion media. A significant effect of CL|MPL and MPL|DM interfaces on liquid transport and flooding is found through the analysis of micro-porous layer (MPL) water content and saturation profile along the CL|MPL and MPL|DM interface region.