Electrospun Carbon Nanofiber Composite Electrode with Gradient Porous Structure for Rapid Ion Transport in an All-Vanadium Redox Flow Battery

This study introduces a novel approach through the design and creation of a composite electrode, uniquely made of three distinct layers of micro/mesoporous electrospun carbon nanofiber (CNF) mats, featuring a gradient in pore size. This innovative gradient pore structure merges the benefits of varying pore sizes, significantly enhancing redox flow battery (RFB) efficiency. The first layer, a microporous CNF mat situated near the membrane, offers an extensive reactive surface area, minimizing charge transfer resistance and speeding up electrochemical reactions—key factors in enhancing battery reaction efficiency. The next layer, a mesoporous CNF mat, fine-tunes the flow properties of the electrolyte, lowering flow resistance while ensuring superior charge transfer capabilities. This structured gradient in pore size not only facilitates improved electrolyte penetration and even distribution but also harmonizes the balance between charge transfer efficiency and electrolyte flow, thus mitigating energy losses without compromising reaction velocity. Charge–discharge testing demonstrated notable performance gains: an energy efficiency of 82% at 100 mA cm⁻² (surpassing traditional electrodes by 71.5%) and 69% at 200 mA cm⁻², alongside a 77.4% increase in peak power density. This advancement not only enhances energy and power densities but also its lifespan, marking a significant step forward for RFB technologies.