Engineering Multimodal Pore Size Distributions in Redox Flow Battery Electrodes via Non-Solvent Induced Phase Separation

Redox flow batteries (RFBs) are promising for large-scale energy storage, but their widespread deployment is limited by elevated capital costs. Advancing porous electrode to achieve high power density is an effective strategy for reducing the system-level costs. Conventional fibrous electrodes are not originally designed for RFBs, resulting in low surface area and suboptimal microstructure. Recently, non-solvent induced phase separation (NIPS) has emerged as a versatile method for fabricating non-fibrous electrodes with engineered architectures. Building on our previous NIPS work, we introduce a nanoparticle-assisted templating strategy to achieve multimodal pore networks. CaCO 3 nanoparticles are incorporated into the polymer solution and subsequently removed to template mesopores within the scaffold. By varying the CaCO 3 loading from 2.5 wt% to 15 wt%, we systematically evaluate the effects on solution rheology, microstructure, pressure drop, and electrochemical performance. The resulting electrodes exhibit trimodal pore networks, enabling high permeability, enhanced electrochemical surface area, and efficient electrolyte transport. Electrochemical testing in vanadium RFBs shows a significant increase in peak power density, with optimal performance achieved at 5 wt% loading (757 mW cm −2 ). These results highlight the benefits of multimodal pore microstructures in RFB electrodes and open a pathway for electrode engineering applicable to other electrochemical technologies.