Solid-state yet flexible supercapacitors made by inkjet-printing hybrid ink of carbon quantum dots/graphene oxide platelets on paper

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  • ReceivedApr 23, 2018
  • AcceptedJun 4, 2018
  • PublishedJun 22, 2018


Paper-based flexible supercapacitors (SCs) show advantages due to the improved adhesion between paper and active materials, the simplified printing process and the lower cost, compared to other substrates such as plastics. Here we report the fabrication of solid-state yet flexible SCs by inkjet-printing a hybrid ink consisting of carbon quantum dots (CQDs) and graphene oxide (GO) platelets, followed by casting of polyvinyl alcohol (PVA)/sulfuric acid (H2SO4) gel electrolyte. The SC obtained from 100-time-printing of the hybrid ink shows a specific capacitance of ~1.0 mF cm−2 at a scan rate of 100 mV s−1, which is enhanced by nearly 150%; the whole device including paper substrate, gel electrolyte and active material demonstrates an energy density of 0.078 mW h cm−3 at a power density of 0.28 mW cm−3. In addition, the excellent mechanical strength of GO platelets ensures the good flexibility and mechanical robustness of the printed SCs, which show a retention of 98% in capacitance after being bended for 1,000 cycles at a bending radius of 7.6 mm. This study demonstrates a promising strategy for the large-scale preparation of low-cost, lightweight, and flexible/wearable energy storage devices based on carbon-based ink and paper substrate.

Funded by

the 1000 Plan Talent Program of China; the MOE NCET Program of China; and the National Natural Science Foundation of China(51322204,51772282)


This work was supported by the Thousand Talents Plan of China, the Program for New Century Excellent Talents in University, and the National Natural Science Foundation of China (51322204 and 51772282).

Interest statement

The authors declare no conflict of interest.

Contributions statement

Zhu Y and Liu J designed this work; Liu J performed the experiments; Liu J and Ye J performed the characterizations; Zhu Y, Liu J, Ye J, Pan F and Wang X analyzed the data; Liu J and Zhu Y wrote the paper; all authors contributed to the discussion and revision.

Author information

Jie Liu is a graduate student at the University of Science and Technology of China. She is currently studying in the Department of Materials Science and Engineering. Her research focuses on the energy storage of new carbon-based composites.

Yanwu Zhu is currently a Professor of the Department of Materials Science and Engineering, University of Science and Technology of China. He obtained a BSc degree in applied physics from the National University of Defense Technology in 2000, a MSc degree in physics from Peking University in 2003, and a PhD degree in physics from the National University of Singapore in 2007. He was a postdoctoral researcher at the National University of Singapore and at the University of Texas at Austin. In the last decade, he has been engaged in the preparation, characterization and property research of graphene and other novel carbon materials.


Supplementary information

Supporting data are available in the online version of the paper.


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  • Figure 1

    (a) Schematic of the fabrication of solid-state SCs. SEM images of (b) blank A4 paper, H-ink printed paper with printing times of (c) 20, (d) 30, (e) 50 and (f) 100 times, respectively.

  • Figure 2

    (a) CV curves of the H-SCs with different printing times at a scan rate of 100 mV s−1. (b) GCD curves of the H-SCs at a current density of 100 μA cm−2. (c) Areal capacitance with respect to the scan rate. (d) CV curves of H-SCs, GO-SCs, and CQDs-SCs with 100 times of printing at a scan rate of 100 mV s−1. (e) GCD curves of H-SCs, GO-SCs, and CQDs-SCs at a current density of 100 μA cm−2. (f) Comparison of areal capacitances of H-SCs, GO-SCs, and CQDs-SCs with respect to the scan rate.

  • Figure 3

    Electrochemical characterizations of H-SCs after the printed electrodes were annealed at 100, 200, 250 and 300°C, respectively. (a) CV curves measured at 100 mV s−1. (b) GCD curves measured at 100 μA cm−2. (c) Comparison of areal capacitances and (d) Nyquist plots of H-SCs with details in the high-frequency region in the inset. (e) FTIR spectra of H-ink printed and annealed at different annealing temperatures. (f) Fraction of peak area for various oxygen groups and the O/C atomic ratio estimated XPS as a function of annealing temperature.

  • Figure 4

    (a) CV curves of the H-SCs-200 under normal and bending conditions at a scan rate of 10 mV s−1. (b) Capacitance retention after 1,000 cycles performed at a bending radius of 7.6 mm at 100 mV s−1, and the inset shows a photograph of the bent device. (c) CV curves of the H-SCs-200 printed on weighing paper at different scan rates. (d) Ragone plots of solid-state H-SCs-200 printed on weighing paper compared with reported values for other solid-state symmetric SCs.

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