New composite hydrogels for energy storage and production

Hydrogels are highly water-absorbent three dimensional viscoelastic networks, mainly based on polymers used in numerous fields such as biotechnology, food and pharmaceutical industry. However, the potential use of these materials in the energy domain has not yet been fully investigated. To bring new insights and perspectives, we have developed during this PhD thesis a spherical macroporous electrode made of a conductive hydrogel. It is composed of sodium alginate, a polyelectrolyte that can form a biocompatible hydrogel when mixed with water in presence of divalent cations. The addition of carbon nanotubes in the solution before gelation leads to the formation of an electronically conductive network. The formulation and the physicochemical characterization are first discussed. Then two direct applications will be detailed. The first one consists in encapsulating electroactive bacteria inside the composite hydrogel. The peculiar metabolism of Geobacter sulfurreducens allows electron transfer with the external medium through oxido-reduction reactions. Current monitoring allows us to show proliferation and viability of the cells until depletion of nutrients in the medium. The second one is the incorporation of intercalation lithium particles in the same matrix for semi-solid redox flow battery domain. Characterization of the redox couple MnO₂/LiMn₂O₄ and FePO₄/LiFePO₄ inside the hydrogel, will enable us to develop a Li-ion battery with a 0.65 V nominal tension. (author)