AbstractsEngineering

Flow batteries are a relatively new promising technology for use with intermittent renewables such as solar or wind power. Much of the research performed on flow batteries focuses on cell or electrode chemistry, with very little work being done to optimize the electrodes' physical properties. This work focuses on designing new electrodes with smaller diameter fibers and therefore higher surface area than current flow battery electrodes. Lower fiber diameter will cause losses in transport properties specifically permeability. To combat this, the materials were designed to have varying degrees of anisotropy which would in turn allow for permeability to vary significantly according to direction. Porous polyacrylonitrile mats were electrospun on an in-house built electrospinning setup. A number of materials were made with varying degrees of anisotropy. In-plane gas permeability measurements were performed in both the parallel and perpendicular directions relative to the fiber alignment. Because the permeability was measured in-plane it was necessary to mechanically compress the samples during measurements. Tests were performed at several compressed thicknesses, but it was found that the samples did not compress uniformly so it was not possible to determine a unique Carman-Kozeny constant for the material. A methodology was developed by which the Carman-Kozeny constant was determined for each compression that produced a linear trend against compressed porosity. It was proposed that the true Carman-Kozeny constant for the material can be determined by extrapolating this trend to the value of the uncompressed porosity, and good agreement with literature values was obtained. These values were used to determine a permeability coefficient which when divided by fiber diameter squared produced dimensionless permeability. The dimensionless permeability data showed very clearly that as the degree of anisotropy increased, the permeability in the direction parallel to the fibers increased and conversely the permeability perpendicular decreased. Simple modelling was performed to confirm the non-linear profile of compression in the materials. The model showed that a parabolic profile was adequate in describing the compression nature of the material. Les batteries à flux sont une nouvelle technologie prometteuse à utilisation intermittente avec les énergies renouvelable telle l'énergie solaire et éolienne. La plupart de la recherche sur les batteries à flux s'attarde sur la chimie cellulaire ou sur celle à l'électrode mais peu d'attention est portée sur l'optimisation des propriétés physiques de l'électrode. Cette étude tente donc d'élaborer de nouvelles électrodes avec des fibres à diamètre plus petit ayant donc une aire de surface beaucoup plus grande que les électrodes conventionnelles. Par contre, des fibres à diamètres plus faibles réduiront certaines propriétés de transport donc la perméabilité. Afin de combattre cet effet, les matériaux sont conçus avec différents degrés d'anisotropie ce qui à la fois varie de manière…