Electrochemical process intensification : from porous electrodes to fluidized bed reactors

Three dimensional electrodes have been widely used until now for environmental applications such as the electrorecovery of metals from dilute effluents, since they offer a high specific surface area allowing to recover metals down to the ppm level. However, such metal electrorecovery on porous electrodes is limited on the one hand by mass transfer, and on the other hand by its intrinsic discontinuous operation to recover the spent metal-covered electrodes. In this thesis, we have explored the use of such 3-D foam structures as gas evolving electrodes for the electrochemical production of hydrogen from water electrolysis. This is an emerging and fastly growing application, closely related to the need for large-scale energy storage solutions associated with renewable (and thus intermittent) electricity production on the MW or even GW scale. It can be expected that both the use of 3D electrodes as well as a switch from batch to continuous operation will allow to significantly reduce the size of water electrolysers, hence opening the way for a much needed electrochemical process intensification. Within this technological context, three main scientific objectives have been pursued. Firstly, to develop and improve experimental methods to electrochemically measure mass transfer limitations in 3D foam electrodes. Secondly, to use these 3D foam cathodes to lower the energy consumption of classical water electrolysers based on low-cost electrocatalyst materials. And finally, to develop a novel rotating fluidized bed reactor where fluidized particles are used as 3D granular electrodes that can be renewed continuously.