Waste-asphalt-derived carbon interlayer enabling uniform CuS deposition for advanced ferricyanide/polysulfide flow batteries

Abstract

Alkaline ferrocyanide-polysulfide redox flow batteries (Fe/S RFBs) have emerged as a promising candidate for grid-scale energy storage, primarily owing to their low raw material costs, intrinsic operational safety, and the inherent decoupling of power and energy in their design. Yet the intrinsically sluggish S₂^2-/S^2- chemistry restricts their power output and cycling durability. To tackle this, we developed a copper sulfide (CuS) and waste-asphalt-derived carbon co-modified carbon felt electrode (CuS-WA/CF), where waste-asphalt pyrolytic carbon serves as an interlayer to guide uniform copper electrodeposition. Subsequently, sulfidation converts the copper into well-dispersed CuS nanoparticles. This rational design increases the specific surface area by approximately 8.4-fold (from 9.55 to 80.46 m² g^-1) and markedly boosts electrochemical activity and conductivity. As a result, the assembled Fe/S RFB with CuS-WA/CF as the anode delivers a peak power density of 259.2 mW cm^-2, which is 61.4% higher than the pristine-CF counterpart. At 40 mA cm^-2, the cell maintained an average energy efficiency (EE) of 77.7% across 10,000 constant-current charge-discharge cycles. In a separate test using a higher-concentration ferrocyanide catholyte and excess anolyte, the cell delivered an average EE of 84.0% across 25,000 capacity-limited cycles. Beyond the performance gains, this work turns waste asphalt into a functional carbon source, offering a low-cost, scalable route toward the practical deployment of Fe/S RFBs for renewable integration.

Keywords

Waste asphalt / pyrolytic carbon interlayer / uniform CuS electrodeposition / polysulfide kinetics / alkaline Fe/S redox flow batteries

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