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Non‐woven carbon nanofiber networks were produced by electrospinning. Electrospinning is a process that can easily be up‐scaled, producing carbon fibers that can be used as electrodes with increased surface area and reaction sites. The structure of electrospun carbon nanofibers (ES‐CNFs) was investigated by scanning electron microscopy and compared to a commercial carbon felt (CF). The electrochemical properties of the obtained ES‐CNFs were studied for the negative half‐cell reaction in a three‐electrode setup and a single‐cell battery test system. The performance and stability of the generated materials were tested by charging and discharging the cell and carrying out X‐ray diffraction and Raman spectroscopy before and after operation. An increase in the energy efficiency of about 10 % was achieved when using five sheets of free‐standing ES‐CNFs compared to commercial CFs, revealing the potential use of ES‐CNFs as electrode materials in the negative half‐cell of all‐vanadium redox flow batteries.

In this work we present a redox-flow battery set-up, into which two reference electrodes were inserted. This system allows for the investigation of individual overpotentials in each half-cell. Further, polarization (E/i) curves were recorded for different states of charge (SOC) of the battery. The performance of pristine and thermally oxidized carbon felts was compared at the negative and positive side of the battery. From the reference electrode measurements we were able to attribute the performance gain of the oxidized felt to the overpotential at the negative half-cell. In contrast the positive side does not seem to improve significantly.

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