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 Fe 2 O 3 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 NH 3 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.