Nitrogen-Doped α-Fe₂O₃ Nanosheets on Stainless-Steel Foils by Anodization for Self-Supported, Flexible, Binder-Free Supercapacitors

Developing high-performance flexible electrodes that balance mechanical strength with electrochemical performance remains a critical issue in the development of flexible supercapacitors. In practical applications, insufficient integration between mechanically robust flexible substrates and electrochemically active materials with high performance remains a major hindrance. In this work, low-cost, flexible stainless steel (SS) was used as a base active material for growing Fe2O3 nanosheets by electrochemical anodization. This approach enabled the fabrication of a binder-free flexible electrode, integrating active materials, a current collector, and a flexible substrate in a single-step anodization process. The anodized flexible electrode achieved a specific capacitance of up to 149 mF cm–2 at 1 mA cm–2. Then, the chemical vapor deposition (CVD) method was utilized for nitride doping of the anodized flexible electrode under NH3 to introduce more oxygen vacancy defects for higher electrical conduction. The nitridized flexible electrode demonstrated a remarkable specific capacitance as high as 479 mF cm–2 at 1 mA cm–2. The cycling properties have also been greatly improved, and the specific capacitance retention is improved from 37.2% of its initial value to 83.6% after 8000 cycles. When the nitridized flexible electrode was utilized as the negative electrode in conjunction with an activated carbon-coated carbon cloth as the positive electrode, the assembled flexible asymmetric supercapacitor achieved an impressive areal specific capacitance of 122.5 mF cm–2. Moreover, after enduring 100 bends at a 90° angle, the device maintained 93.5% of its specific capacitance after 2000 cycles, highlighting its exceptional mechanical and electrochemical properties.