Abstract

High electrochemical conversion rates can be obtained if the ratio of electrode surface to solution volume is maximized. In this context, packed bed electrodes consisting of fine conductive particles offer exceptionally high specific surfaces. However, in case of electrochemical reactions involving suspended solids or gases, packed bed electrodes are not suitable due to the risk of blockage. Fluidized bed electrodes can avoid this risk, but encounter problems regarding the electrical contacting between the electrode particles. In this work, we show that a magnetic stabilization of the fluidized bed electrode improves the contacting of the electrode particles and results in strongly improved yields. With electrode particles having a mean size of 175 µm and consisting mainly of carbon and magnetite, it was found that the yield of the reduction of a 3 mM potassium ferricyanide solution approached 100% when flowing through the fluidized bed with superimposed magnetic field, while the yield was less than 50% without the application of a magnetic field. To achieve this enhancement, the effective electrode surface of the fluidized bed must be increased by up to 400% when applying a magnetic flux density of 20 mT. Our results show that the magnetic stabilization of a fluidized bed electrode significantly improves the usability of this type of electrochemical reactor. We anticipate that the designed reactor will be a starting point for further investigations of applying fluidized bed electrodes for challenging electrochemical processes including solids and gases, as they can be found for example in waste water treatment or electro-biotechnology.

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