We report results of polarization measurements resolved for the negative and positive electrodes of vanadium redox batteries (VRBs) using a dynamic hydrogen electrode in an operating battery cell. Electrochemical experiments with symmetric electrolyte feeds were also performed. Greater kinetic polarization is observed at the negative (V 3/2+) electrode compared to the positive electrode (V 5/4+), in contrast with previously reported ex situ measurements. For the positive electrode, the polarization in the low-current regime was modest and was not kinetically controlled. The relative rates of reaction are a surprise since it might be expected that the V 3/2+ redox reaction is a simple outer-sphere electron transfer.

Sulfonated Diels-Alder poly(phenylene) (SDAPP) membranes were synthesized and characterized as potential electrolyte separators for vanadium redox flow batteries. The SDAPP membranes studied had ion exchange capacities of 1.4, 1.8 and 2.3 meq/g. Transmission electron microscopy imaging shows that the ionic domains in SDAPP are roughly 0.5 nm in dimension, while Nafion has a hydrophilic phase width of around 5 nm. The sulfuric acid uptake by SDAPP was higher than that for Nafion, but the materials had similar water uptake from solutions of various sulfuric acid concentrations. In equilibration with sulfuric acid concentrations ranging from 0-17.4 mol · kg −1 , SDAPP with a IEC of 2.3 meq/g had the highest conductivity, ranging from 0.21 to 0.05 S · cm −1 , while SDAPP with a IEC of 1.8 had conductivity close to Nafion 117, ranging from 0.11 to 0.02 S · cm −1 . With varying sulfuric acid concentration and temperature, vanadium permeability in SDAPP is positively correlated to the membrane's IEC. The vanadium permeability of SDAPP 2.3 is similar to that of Nafion, but permeability values for SDAPP 1.8 and SDAPP 1.4 are substantially lower. The vanadium permeation decreases with increasing electrolyte sulfuric acid concentration. Vanadium diffusion activation energy is about 20 kJ · mol −1 in both SDAPP and Nafion.The vanadium redox flow battery (VRFB) has shown technical potential for large scale electrical energy storage. 1-3 One possible role of VRFBs is their integration with the electrical grid to "level off" supply and demand mismatches and to improve overall reliability and efficiency of the grid. 1 Another scenario for VRFB use is buffering stochastic energy sources, such as solar or wind, which will improve the stability of electricity output from these renewable resources. 1,4 A VRFB is essentially a regenerative fuel cell, with a flowing operation pattern similar to proton exchange membrane fuel cells. 5,6 In a VRFB the energy is carried by vanadium redox couples V 5+ /V 4+ and V 2+ /V 3+ in electrolyte solutions. The energy is interconverted between electrical and electrochemical forms by the battery cell or stack, where the functional core is the membrane electrode assembly. The function of the membrane is to separate positive and negative electrolyte solutions and conduct ionic current, while vanadium redox reactions take place on the electrode surface in each half-cell. During battery operation, electrolyte solutions are constantly fed through the battery to support electrochemical reactions and to generate steady current output or recharge the electrolyte solution.In the VRFB cell, the electrolyte separator is a primary limiting factor in the battery's performance. 3 As has been demonstrated, resistance from the separator is the most important source of the battery's internal resistance, impeding battery performance during high current density operation. 3,7 Ideally, the electrolyte separator should have high conductivity to minimize battery efficiency losses caused by internal resistance and also hig...

Many previous studies have focused on the surface M proteins of group A streptococci (GAS) as virulence determinants and protective antigens. However, the majority of GAS isolates express M-related protein (Mrp) in addition to M protein, and both have been shown to be required for optimal virulence. In the current study, we evaluated the protective immunogenicity of Mrp to determine its potential as a vaccine component that may broaden the coverage of M protein-based vaccines. Sequence analyses of 33 mrp genes indicated that there are three families of structurally related Mrps (MrpI, MrpII, and MrpIII). N-terminal peptides of Mrps were cloned, expressed, and purified from M type 2 (M2) (MrpI), M4 (MrpII), and M49 (MrpIII) GAS. Rabbit antisera against the Mrps reacted at high titers with the homologous Mrp, as determined by enzyme-linked immunosorbent assay, and promoted bactericidal activity against GAS emm types expressing Mrps within the same family. Mice passively immunized with rabbit antisera against MrpII were protected against challenge infections with M28 GAS. Assays for Mrp antibodies in serum samples from 281 pediatric subjects aged 2 to 16 indicated that the Mrp immune response correlated with increasing age of the subjects. Affinity-purified human Mrp antibodies promoted bactericidal activity against a number of GAS representing different emm types that expressed an Mrp within the same family but showed no activity against emm types expressing an Mrp from a different family. Our results indicate that Mrps have semiconserved N-terminal sequences that contain bactericidal epitopes which are immunogenic in humans. These findings may have direct implications for the development of GAS vaccines.

not Available.

not Available.