Cu-coated Bi2O3 on plasma-activated carbon cloth as a high-performance supercapacitor electrode

Flexible battery-type supercapacitors are often limited by sluggish interfacial charge transfer and poor adhesion of active materials on carbon cloth, leading to rapid performance decay under high-rate cycling. Here, we combine O2/N2 plasma activation, hydrothermal growth of Bi2O3, and Cu magnetron sputtering to construct a hierarchical Cu–Bi2O3/plasma-activated carbon electrode on carbon cloth without a conventional carbon overlayer. The mixed O2/N2 RF plasma introduces nanopores and O/N-containing functional groups onto carbon fibers, improving wettability and creating anchored surface sites for homogeneous Bi2O3 nanosphere growth. An ultrathin sputtered Cu overlayer is deposited onto the Bi2O3/plasma-activated carbon electrode, acting as a conductive shell that bridges Bi2O3 nanospheres and the carbon substrate, reinforcing contact, reducing interfacial resistance, and improving active-material utilization. SEM, TEM, XRD, and XPS confirm this plasma-engineered architecture and a conformal Cu coating. Electrochemical tests in 6 M KOH reveal accelerated redox kinetics, reduced charge-transfer resistance, and good rate performance. The electrode delivers an areal capacitance of 4086.3 mF cm−2 at 1 mA cm−2 and retains 84.2% after 5000 cycles. Overall, these findings suggest a practical, potentially general strategy for designing high-performance carbon/transition-metal-oxide composite electrodes for supercapacitors.