MOF-Derived Fe2O3@Fe3O4-Coated Carbon Fiber Fabric as a Negative Electrode for Flexible Supercapacitors

Owing to the increasing demand for wearable electronics, flexible energy storage devices, such as supercapacitors, have gained interest in the electronic industry. In this context, asymmetric configurations have emerged as a promising strategy for the development of wider potential window supercapacitors. On the other hand, MOF-derived synthesis of transition metal oxides is known to result in porous materials, which exhibit better electrochemical performance. In this work, a MOF-derived Fe2O3 coating on carbon fiber woven substrate is proposed as a negative supercapacitor electrode for asymmetric flexible devices. Moreover, the MOF calcination time was evaluated in order to ensure the best electrochemical performance possible, achieving for the sample calcined for 2 h a specific capacitance of 18.8 F/g at a current density of 200 mA/g and an excellent rate capability. In addition, not only was this promising material obtained, but an asymmetric flexible supercapacitor based on two MOF-derived TMO coatings on carbon fiber woven electrodes was manufactured and characterized as a proof of concept. This supercapacitor displayed a specific capacitance of 229 mF/cm2, an energy density of 0.067 mWh/cm2 and a power density of 0.11 mW/cm2 at 0.15 mA/cm2. Moreover, the flexible supercapacitor retained 94.1% of its capacitance even after being bent to 90°.