High-performance binder-free RuO₂/electrospun carbon fiber for supercapacitor electrodes

Binder-free RuO₂/carbon fiber composite electrodes were prepared by depositing RuO₂ on electrospun carbon fibers using the incipient wetness impregnation method. The amount of RuO₂ in the composites monotonically increased with the number of impregnation cycles. When the composite was thermally treated at 300 °C, RuO₂ particles coalesced to form a wrinkle-like structure. Additionally, hydrous RuO₂ partly converted to crystalline RuO₂. We demonstrated that the relative contents of crystalline and hydrous RuO₂ were closely related to the amount of RuO₂ in the composite: the crystalline RuO₂ content increased, whereas the hydrous RuO₂ content decreased with an increase in the amount of RuO₂ in the composite. When the composites were used as supercapacitor electrodes, the specific capacitance increased and then decreased with the amount of RuO₂ in the composite. The maximum capacitance of 544 F/g in 2 M of H₂SO₄ at a scan rate of 2 mV/s was achieved with an RuO₂ content of 12.23%; this was attributed to the favorable RuO₂ content in the composite and the suitable amounts of hydrous/crystalline RuO₂. When the amount of RuO₂ in the composite was high, RuO₂ caused fiber fracture during electrochemical reactions, resulting in poor electrode stability.