High-performance supercapacitors using carbon dots/titanium dioxide composite electrodes and carbon dot-added sulfuric acid electrolyte

Abstract

The H 2 SO 4 system used carbon dots as electrode/electrolyte additives. The charge storage of pristine titanium oxide is dominantly controlled by the surface mechanism. Carbon dots act as pseudocapacitive boosters via improving surface wettability, interaction at the electrode/electrolyte interface, and the diffusion-controlled process. The supercapacitors achieved the highest areal specific capacitance of 643 mF cm -2 , representing a total enhancement of 1,261%. • The carbon dots were used as additives in TiO 2 /H 2 SO 4 -based supercapacitors. • The capacitance was enhanced of 237% by adding carbon dots in TiO 2 electrode. • The capacitance was further improved by 292% by adding carbon dots in H 2 SO 4 . • An areal specific capacitance of 643 mF cm −2 was obtained with 98.4% retention. • The overall enhancement is 1,261% better than pristine TiO 2 and H 2 SO 4 system. Herein, the electrochemical performance of nanocomposite comprised of TiO 2 nanoparticles and sodium polyacrylate-derived carbon dots (CDs) was investigated in H 2 SO 4 electrolyte. The specific capacitance of 5% w/w CDs-containing TiO 2 electrode in 1 M H 2 SO 4 demonstrated a significant enhancement of 237%, compared to pristine TiO 2 . Interestingly, when added to the electrolyte, the specific capacitance was further increased by 292% or as high as 643 mF cm −2 . As a result, the addition of CDs in both electrode and electrolyte produced overall improvement of 1,261% through favorably synergistic effects of lessening the series resistance, enhancing surface wettability, diffusion-controlled contribution, and pathways for ion diffusion. These findings are confirmed by thorough electrochemical analysis and data fitting. To the best of our knowledge, this supercapacitor gave the highest areal capacitance value among prior reports of TiO 2 -based supercapacitors containing H 2 SO 4 electrolytes. Furthermore, it also delivered a high areal energy density of 24.3 μWh cm −2 at a power density of 187.5 μW cm −2 and extraordinary cycling stability of 98.4% capacitance retention after 5,000 cycles. Our work proved that the utilization of CDs as pseudocapacitance promoters and ion facilitators can significantly improve the supercapacitor performance. This strategy will be an innovative way to develop energy storage devices with high performance, excellent stability, simple manufacturing process, and low production cost for practical applications.