Design and fabrication of printed Graphene paper based micro-supercapacitor device with a Redox-active electrolyte

Introduction Inspired by future needs of flexible, simple and low-cost energy storage devices, we designed smart graphene based micro-supercapacitors on ordinary paper substrates using redox-active aqueous electrolytes which... [ view full abstract ]

Introduction
Inspired by future needs of flexible, simple and low-cost energy storage devices, we designed smart graphene based micro-supercapacitors on ordinary paper substrates using redox-active aqueous electrolytes which can have great applications in portable electronics. This printed graphene device exhibited a maximum volumetric capacitance of 87.6 mF/cm3 (1.95 mF/cm2) at 3.2mA/cm3. Later, the performance was tested in hybrid electrolyte which was prepared by adding a redox-active species (potassium iodide, KI) in 1 M H2SO4. The results were remarkably improved with excellent volumetric capacitance of 813 mF/cm3 at 37.5 mA/cm3 (30.7 mF/cm2) (one order of magnitude higher).
Method
Briefly, graphene dispersion in water (2mg/ml) was printed over the two sides of conventional paper without any pre-treatment by stamping technique [1]. Further the printed electrodes were then soaked in either H2SO4 or H2SO4 containing different concentrations of KI (0.05 M, 0.1 M and 0.2 M) for 5 min and used for further measurements. All the values are given normalized per volume (cm3) of the total device.
Results and discussion
Figure 1a shows the TEM image of the graphene nanosheet which shows that the nanosheets are thin and transparent with extra-large size, inset is the electron diffraction pattern that confirms the formation of graphene. Figure 1(b) show the cyclic voltammetry (CV) curves in conventional H2SO4 and KI-doped H2SO4 electrolyte. It is revealed that area under the CV curves increases and is distorted from ideal rectangular shape (obtained from EDLC) suggesting increase in total capacitance and involvement of redox active KI. Galvanostatic charge/discharge curves are strongly in agreement with CV results (see Figure 1 c) and shows prolonged time for discharge indicating high energy and capacitance. The maximum volumetric capacitance was found to be 813 mF/cm3 for 0.1M KI+H2SO4 electrolyte which is one order of magnitude higher than the conventional H2SO4 electrolyte (Fig. 1d). The device achieved maximum energy and power densities of 0.29 mWh/cm3 and 73.6 mW/cm3, respectively, Figure 1(e). Finally, Figure 1(f) shows 97% capacitance retention over 1000 charge-discharge cycles for this device.
References
[1] Luis Baptista-Pires, Carmen C. Mayorga-Martínez, Mariana Medina-Sanchez, Helena Monton, and Arben Merkoci̧, ACS Nano 2016, 10, 853−860