Energizing Fe2O3-based supercapacitors with tunable surface pseudocapacitance via physical spatial-confining strategy

Developing an anode with outstanding electrochemical properties remains a significant challenge in building high-performance asymmetric supercapacitor devices. The promising Fe2O3-based anode shows exceptional theoretical electrochemical performance but limited by its undesired practical energy density and long-term cycling stability. Herein, we propose a physical spatial-confining strategy to enhance the electrochemical performance of the Fe2O3-based electrode with tunable surface pseudocapacitance using redox electrolyte Na2SO3. By introducing Al2O3 nanograins on the surface of Fe2O3, electrolyte Na+ can diffuse through the surface-anchored Al2O3 nanograin but SO32- was physically blocked due to the Na+ ions fast diffusion nature of Al2O3 during the electrochemical operations. And a positive charge center by Na+ was formed on the side of Fe2O3, which attracts SO32- securing a stable bridge between the dissociative SO32- groups and electrode. Such a physically constrained structure ensures the fast dual-ion-involved redox reactions, leading to a significant electrochemical performance (including capacitance performance and long-term cycling stability). The Al2O3/Fe2O3-based anode delivers a high capacitance of 2371F g(-1) at 5 mV s(-1) with a capacitance retention of 1277F g(-1) even at 200 mV s(-1), which also shows superior cycling stability of 95.38% after 5000 cycles. A novel dual-electrolyte Al2O3/Fe2O3@CNTs/Na2SO3//MnO2@CNTs/Na2SO4 asymmetric supercapacitor device with a potential window of 0-2.2 V was configured, which shows the remarkable performance of energy density of 174 W h kg(-1) at a power density of 4492 W kg(-1).