Metal-free platforms for molecular thin films as high-performance supercapacitors

Abstract

Controlling chemical functionalization and achieving stable electrode–molecule interfaces for high-performance electrochemical energy storage applications remain challenging tasks. Herein, we present a simple, controllable, scalable, and versatile electrochemical modification approach of graphite rods (GRs) extracted from low-cost Eveready cells that were covalently modified with anthracene oligomers. The anthracene oligomers with a total layer thickness of ∼24 nm on the GR electrode yield a remarkable specific capacitance of ∼670 F g⁻¹ with good galvanostatic charge–discharge cycling stability (10 000) recorded in 1 M H₂SO₄ electrolyte. Such a boost in capacitance is attributed mainly to two contributions: (i) an electrical double-layer at the anthracene oligomer/GR/electrolyte interfaces, and (ii) the proton-coupled electron transfer (PCET) reaction, which ensures a substantial faradaic contribution to the total capacitance. Due to the higher conductivity of the anthracene films, it possesses more azo groups (–NN–) during the electrochemical growth of the oligomer films compared to pyrene and naphthalene oligomers, which is key to PCET reactions. AC-based electrical studies unravel the in-depth charge interfacial electrical behavior of anthracene-grafted electrodes. Asymmetrical solid-state supercapacitor devices were made using anthracene-modified biomass-derived porous carbon, which showed improved performance with a specific capacitance of ∼155 F g⁻¹ at 2 A g⁻¹ with an energy density of 5.8 W h kg⁻¹ at a high-power density of 2010 W kg⁻¹ and powered LED lighting for a longer period. The present work provides a promising metal-free approach in developing organic thin-film hybrid capacitors.