Interfacial Charge Transfer Activates Graphene Shells for High-Efficiency and Durable Vanadium-Cerium Redox Flow...

Vanadium-cerium redox flow batteries (V-Ce RFBs) have emerged as a promising alternative to all-vanadium systems, owing to their higher operating voltage and reduced material costs. However, their practical implementation is hindered by the sluggish kinetics of the Ce³⁺/Ce⁴⁺ redox reaction, and previous strategies have often yielded only marginal performance gains or inadequate stability under strongly acidic conditions. Herein, we develop a novel electrocatalyst comprising iron-cobalt alloy nanoparticles encapsulated with a graphene shell (FeCo@Gr) for the positive electrode of V-Ce RFBs. The graphene layer not only serves as a corrosion-resistant barrier but also exhibits high catalytic activity for Ce³⁺/Ce⁴⁺ redox reaction due to electron transfer from electronic coupling with the alloy core. The FeCo@Gr-modified electrode demonstrates significantly improved catalytic activity for the Ce³⁺/Ce⁴⁺ redox reaction compared to pristine GF. In a single-cell battery test, it achieves an energy efficiency of 63.4% at 200 mA cm^-2 and a peak power density of 433 mW cm^-2, substantially exceeding the performance of the unmodified electrode. Density functional theory calculations indicate that the electron-rich graphene layer facilitates charge transfer and lowers the reaction energy barrier. This work provides an effective strategy for developing durable and high-performance electrocatalysts for flow battery applications.