Bimetallic Ru_xV_1-x alloy nanoparticles encapsulated tubular carbon fibers for boosting electrochemical capacitors

The growing demand for high-energy and high-power-density energy storage devices has accelerated advancements in electrochemical capacitors, renowned for their fast charge/discharge rates, high power density, and excellent durability. In this study, we present a straightforward strategy for fabricating bimetallic Ru_xV_1–x nanoparticles embedded in nitrogen-doped carbon nanofibers (CNFs), uniformly distributed with a narrow size range on the CNF surface, as efficient electrode materials to enhance capacitive performance. By tuning the molar ratio of ruthenium to vanadium, the crystal phase of Ru_xV_1–x within the CNFs can be precisely modulated to optimize electrochemical behavior in aqueous electrolytes. Among the various Ru_xV_1–x-CNF hybrid nanostructures, the Ru1V1–10 % based electrode exhibits outstanding capacitance and rapid charge–discharge characteristics. The Ru1V1–10 % electrode exhibited a high capacitance of 206–175 Fg⁻¹ (1–20 mA cm⁻²) in 6 M KOH and delivered 24.8 Whkg⁻¹ at 400 W kg⁻¹, while retaining 94 % of its capacitance after 10,000 cycles. These superior properties are primarily attributed to its high surface area and abundant mesopores of CNT structures including the synergistic benefit of a large number of electroactive sites within the crystalline Ru_xV_1–x nanoparticles. The enhanced mesoporosity and crystallinity facilitate efficient electrolyte transport and greater charge accumulation, thereby boosting overall performance. Notably, despite utilizing a smaller quantity of precursors for embedding Ru_xV_1–x nanoparticles into the CNFs, the resulting electrode achieves a threefold increase in specific capacitance compared to the pristine CNF electrode. Thus, optimizing the interplay between surface area, mesoporosity, and the crystalline phase of Ru_xV_1–x is essential for maximizing the capacitive performance of Ru_xV_1–x-CNF hybrid nanostructures.