Molecular engineered A–D–A–D–A organic electrode system for efficient supercapacitor applications

Abstract

Pseudocapacitors (PSCs) play a key role in energy storage (ES) technology development today. PSCs offer higher energy density as compared to their inorganic counterparts. Moreover, as compared to battery systems, they also exhibit higher power density for a shorter duration of time. In the present investigation, we designed, synthesized and demonstrated a novel acceptor (A)–donor (D)–acceptor (A)–donor (D)–acceptor (A) molecular architecture comprising naphthalene-1,4,5,8-tetracarboxylic diimide (NDI), tryptophan (Trp) and dopamine (DP) organic components. The as-fabricated NDI-Trp-DP/graphite foil (GF) electrode material was employed for three-electrode supercapacitor (SC) and two-electrode symmetric supercapacitor (SSC) device fabrication. The NDI-Trp-DP/GF material exhibited pseudocapacitive behaviour with an excellent specific capacitance (C_sp) of about 267.90 F g⁻¹ at a scan rate of 5 mV s⁻¹ (cyclic voltammetry, CV) and 323 F g⁻¹ at a current density 0.5 A g⁻¹ (galvanostatic charge–discharge, GCD) in a three-electrode SC and a C_sp of 152 F g⁻¹ at 0.5 A g⁻¹ in two-electrode SSC device systems. The NDI-Trp-DP/GF electrode exhibits an excellent cycling stability of about 95.87% after 10 000 galvanostatic charging–discharging (GCD) cycles and 97.76% continuous GCD charge–discharge cycling coulombic efficiency. The enhanced C_sp and cycling stability performance of the NDI-Trp-DP/GF electrode results from the reversible redox reactions of the organic subunits present in the molecule, faster ion diffusion, and improved mechanical and chemical stability. This novel A–D–A–D–A design offers an efficient way to improve the electrochemical performance of PSCs. The design of this molecular engineered architecture and its redox properties with excellent cycling stability will help to fabricate future PSC-based electronics.