Enhanced supercapacitor performance of anodized stainless steel flexible electrode coated by electron cyclotron resonance carbon film

Electrochemical anodized stainless steel is hopeful serving as free-standing electrode in flexible supercapacitor for the low-cost, eco-friendly and binder-free characteristics. However, the unsatisfactory cycling stability prevents the practical use towards wearable electronics. Herein, we introduce a conductive carbon film deposited on the surface of anodized stainless steel electrode as a protection layer via electron cyclotron resonance sputtering. By optimizing the deposition bias voltage and deposition time, the accomplished flexible electrode exhibits a specific capacitance of 271.6 mF·cm^-2 at a current density of 1 mA·cm^-2, a 2.24-fold increase over the uncoated counterpart, with 88.7% capacitance retention after 8,000 cycles. The elevated performance is highly related to the conductivity of surface coating, resulting from the sp2/sp3 ratio. The carbon film coated anodized stainless steel electrode is combined with activated carbon on carbon cloth electrode and gel electrolyte to produce flexible supercapacitor. The energy storage device exhibits a wide operating potential window of 1.8 V, a high energy density of 51.70 mWh·cm^-3, and a power density of 0.50 W·cm^-3, accompanied by robust flexible stability. Our findings may pave the way for increasing the reliability of high-performance, flexible, and cost-effective supercapacitors, which are compatible with large-scale semiconductor device manufacturing as well.