Structural composite supercapacitor using carbon nanotube mat electrodes with interspersed metallic iron nanoparticles

A carbon nanotube (CNT) mat interspersed with metallic iron nanoparticles is investigated as a structural supercapacitor electrode material that could be incorporated into fiber-reinforced composites. Both ionic liquid and aqueous potassium hydroxide electrolytes are trialed to examine pseudocapacitive mechanisms and the long-term electrochemical stability of the CNT mat in symmetrical supercapacitors. High-resolution transmission electron microscopy showed the high level of interconnection of the CNTs and evenly distributed metallic iron nanoparticles, which enhances the structural and electrical performance of the electrode. Raman and X-ray photoelectron spectroscopies combined with thermogravimetric and surface area analyses are used to characterize the physico-chemical properties of the CNT mat and identify the different electrochemical mechanisms contributing to the supercapacitive behavior. Three electrode experiments demonstrated the relative contributions of the cathode and anode processes to the total capacitance. Symmetrical supercapacitor coin-cell trials used a structural glass-fiber separator and showed the ionic liquid electrolyte facilitated stable pseudocapacitance with the available iron nanoparticles, leading to specific energy and power as high as 18.3 Wh.kg−1 at 0.15 kW kg−1 and 5.6 Wh.kg−1 at 2.4 kW kg−1 after 5000 cycles. It is envisioned these materials can readily be incorporated into composite materials for structural energy storage technology. [Display omitted] •Well characterized self-standing CNT mat electrode for structural composite supercapacitors.•Electrochemical pseudocapacitance adds to total capacitance and is retained after 5000 cycles.•Commercial woven glass fiber cloth is used successfully as separator material.•All components are compatible with fiber reinforced polymer composites and their manufacturing techniques.•Successful electrochemical and structural testing of integrated supercapacitor in carbon fiber reinforced composite.