Capacitive charge storage of tetraphenylporphyrin sulfonate-CNT composite electrodes

•A sulfonated porphyrin-CNT composite electrode was developed for capacitive storage.•A < 2 nm porphyrin on CNT led to higher capacitance and faster kinetics than pure CNT.•The synergy was related to the reduced HOMO-LUMO gap in porphyrin deposited on CNT.•The porphyrin depositions on CNT was confirmed by vibrational and surface analyses.•The symmetric capacitor also had low interfacial resistance and fast rate response. A tetraphenylporphyrin sulfonate-carbon nanotube (TPPS-CNT) composite was developed and characterized for capacitive charge storage. Density functional theory (DFT) simulations suggested that the adsorption of TPPS on CNT was energetically favored with a strong contribution of the sulfonate groups. The composite electrodes, with a < 2 nm TPPS layer, had up to 80 % increase in volumetric capacitance and faster kinetics over the bare CNT electrodes. The adsorption of TPPS on CNT also led to a 9 % reduction in HOMO-LUMO gap of TPPS, which could be the origin of the synergy for improved performance. The highly capacitive TPPS-CNT composite electrode also had high cycling stability after 10,000 cycles. In a two-electrode symmetrical device, the TPPS-CNT maintained a higher capacitance than that of the CNT device. The device based on the composite materials also had lower charge transfer resistance and faster rate response, very promising for high-rate electrochemical charge storage. [Display omitted]