Unlocking the potential of vanadium redox flow batteries: Recent advances in biomass lignin-based carbon fibers and future outlook

Electrode materials play a pivotal role in determining the performance of redox flow batteries (RFBs), which are emerging as efficient and scalable energy storage systems for renewable energy integration. Conventional electrode materials such as graphite and carbon felt, while effective, are expensive and environmentally taxing. As a sustainable alternative, biomass-derived carbon fibers (BCFs) and lignin-derived carbon (LDC) have attracted significant attention due to their low cost, environmental friendliness, and desirable electrochemical properties. BCFs offer high surface area, excellent electrical conductivity, and mechanical durability, making them well-suited for RFB electrodes. Their performance can be further enhanced through physical and chemical activation processes that increase porosity and surface functionality. Lignin, a complex and abundant phenolic biopolymer, serves as a promising carbon precursor due to its high carbon content, thermal stability, and intrinsic redox activity. Through carbonization and activation, lignin can be converted into high-conductivity carbon materials with tunable properties for electrochemical applications. This review critically evaluates the current progress in the development and application of BCFs and LDCs in RFBs, highlighting how their integration can enhance electron transport, ion accessibility, and long-term stability. The combined use of these materials not only improves RFB efficiency but also contributes to reducing the overall carbon footprint of energy storage systems. Finally, the review identifies key challenges and outlines future research directions aimed at optimizing material synthesis, improving performance, and enabling large-scale implementation to support a more sustainable energy infrastructure.