Electrospun composite fiber electrodes with balanced permeability coefficient and specific surface area for vanadium redox flow batteries

To address the trade-off between electrode permeability and specific surface area in vanadium redox flow battery, this paper proposes a novel electrode structure termed the directional mesh composite fiber electrode (DMFE). This electrode structure employs a directional fiber electrode (DFE) as the transport layer and a mesh fiber electrode (MFE) as the catalytic layer, effectively alleviating concentration gradients along both the through-plane and in-plane directions within the electrode while maintaining satisfactory electrochemical performance. DMFE is continuously fabricated via electrospinning, and this integrated preparation process effectively eliminates the contact resistance between the two electrode layers. The feasible ranges of porosity and fiber diameter for each layer are first determined experimentally, after which a genetic algorithm is employed to identify the optimal structural matching scheme, thereby exploiting the structural advantages of the gradient electrode. Experimental results show that MFE fiber diameter can be achieved in the range of 0.20 to 1.02 μm, whereas DFE fiber diameter is fixed at 3.89 μm. The corresponding porosity ranges are 0.80 to 0.90 for MFE and 0.85 to 0.95 for DFE. According to the genetic algorithm optimization, the optimal matching scheme for DMFE consists of a transport layer with a fiber diameter of 3.89 μm and a porosity of 0.85, and a catalytic layer with a fiber diameter of 1.01 μm and a porosity of 0.90. At a current density of 100 mA·cm⁻², the energy efficiency of DMFE assembled cell reaches 75.84%, which is 11.25% higher than that of the cell using DFE alone.