A spray coated high performing metal-free onion-like carbon supercapacitor for sustainable energy storage

Supercapacitors will play a crucial role in the future energy landscape due to their high power density and extended cycle stability. However, energy density tends to be relatively low, partly because of conventional heavy current collectors, also posing sustainability issues. It is crucial to integrate lightweight, flexible current collectors and environmentally friendly active materials while maintaining the performance of the super- capacitor. Here we report on a metal-free supercapacitor using a carbon paper current collector and onion like carbon (OLC). The electrodes were fabricated through a scalable and flexible spray-coating process using onion- like carbon ink. Higher capacitances were observed for the paper-based electrode (24.1 F/g, 34.9 mF/cm(2)) compared to 22.5 F/g (31.5 mF/cm(2)) for aluminium collectors at scanrates of 2.5 mV/s over a voltage window of 2.5 V. At elevated scanrates of 100 mV/s-5 V/s, the actual operating window of a supercapacitor, the paper- based electrode offers a significantly enhanced performance. Stability tests demonstrated a capacitive retention of 98 % for both electrodes after 10,000 cycles. The utilization of onion-like carbon as the active material and a paper-based current collector enables the development of a fully carbon-based supercapacitor system, without compromising its electrochemical performance. This approach introduces a metal-free OLC super- capacitor and promotes environmental sustainability by reducing the dependence on conventional metal-based components and provides a more resource-efficient solution to address the energy storage needs.