LAUSR

Three-dimensional (3D) continuous carbon filament electrodes prepared with tailored fiber placement (i.e. embroidered electrodes) were investigated in a 300 cm2 redox flow cell with 50% state-of-charge ferro/ferricyanide redox couple as probe electrolyte. Electrochemical impedance spectroscopy was performed to identify the different resistance contributions, and thus voltage losses of the electrodes. The outcomes demonstrate that: (1) High-frequency resistance values comparable to the felts can be achieved through side contacting of continuous filament electrodes to the graphite plates instead of pressing the whole electrode structure; (2) The pressure drop can be minimized with the embroidered electrodes, independently of the electrode thickness, attributed to a reduced hydraulic resistance due to the parallel orientation of the carbon filaments to the electrolyte flow; (3) An oxidation treatment to improve the wettability of the electrodes to reduce charge-transfer resistances is required, as well as an optimization duration of the activation treatment to avoid filament breakage due to etching; and (4) An enhancement of mass transfer coefficients in the embroidered electrodes was observed as compared to the felts, which was attributed to the perpendicular orientation of the carbon filaments to the electrolyte flow. The paper provides avenues for further development of 3D carbon fiber electrodes.