Graphite microparticles as bifunctional component for constructing high-performance electrode with gradient structure for vanadium redox flow batteries

The performance of vanadium redox flow batteries (VRFBs) is decisively influenced by the electrode. The key properties of electrode, including surface activity, electrical conductivity, and mass transfer performance, often display a contradictory trade-off relationship. Gradient design can effectively harmonize these critical properties of electrodes and achieve enhanced battery performance. In this study, graphite microparticles with several micrometers in size, are concurrently introduced into the PAN-based electrospinning precursor solution. By controlling the content of graphite microparticles (GMPs) and employing stepwise electrospinning, carbon nanofiber electrode with gradient components and pore structures can be fabricated. The side with more GMPs and larger pore size interfaces with the bipolar plate and liquid inlet, enhancing mass transfer and reducing contact resistance. Conversely, the dense side without GMPs interfaces with the membrane, shortening the ion-electron transport path and protecting the membrane from damage caused by vertical fibers. The gradient structure is also advantageous for preventing fiber breakage and structural collapse that may result from an excessive amount of GMPs. The VRFB assembled with a gradient electrode demonstrated an energy efficiency 4.18% higher than that of the conventional battery, which verifies the feasibility of this gradient electrode design.