Wearable fabric supercapacitors based on CNTs and polyhedral ZnO with a wide potential window

Wearable electronic devices such as health monitors, sensors, and e-skin can be powered by lightweight, high-power supercapacitors. Using a binder-free and low-temperature hydrothermal method, polyhedral ZnO nanoparticles were grown on carbon nanotube (CNT)-decorated cotton fabric, which is friendly to human skin and highly wearable, inexpensive, and thus commercially viable. The concentration of the starting material, zinc acetate, was varied to optimize the electrochemical performance. The evenly spaced polyhedral ZnO facilitated efficient permeation of the electrolyte into the active material. The fabric filaments were decorated with CNTs to enhance electron transfer and the overall electrochemical processes. The symmetric cell comprised of cotton fabric decorated with ZnO polyhedron/CNT showed no discernible change in the cyclic voltammetry curves even after 500 bending cycles, demonstrating the mechanical durability of the electrode. The potential window of 1.6 V using a Na₂SO₄/K₂SO₄ aqueous dual-ion electrolyte improved the long-term electrochemical stability and increased the energy storage capacity. The capacitance retention was 94% after 5000 cycles at a current density of 1 A·g⁻¹, indicating long-term electrochemical stability. A specific capacitance of 375 F·g⁻¹ at a current density of 5 A·g⁻¹ and energy density of 33.3 Wh·kg⁻¹ at a power density of 2000 W·kg⁻¹ were recorded for the optimized electrode. Highlights: Polyhedral ZnO was grown on cotton fabric using a hydrothermal process. The electrochemical performance was optimized by varying the zinc acetate concentration. The highest specific capacitance was 375 F·g⁻¹ at a current density of 5 A·g⁻¹. Under optimal conditions, the capacitance retention was 94% at N = 5000 cycles. The energy density of the electrode was as high as 33.3 Wh·kg⁻¹.