A 3D printed solid-state supercapacitor, 3D-SC, is developed to evaluate the potential of this 3D printable graphene filament utilising two 3D printed discs and sandwiching a solid electrolyte between the two, creating a fully freestanding supercapacitor. The solid electrolyte is prepared by mixing 6 g polyvinyl acetate (PVA) with 10 mL of 1.0 M H2SO4 (as mentioned in the Methods section), leaving a completely freestanding solid-state structure utilising 3DEs, depicted in the inset of Fig. 4A. Upon creation of the 3D-SCs, cyclic voltammetric analysis was carried out, with the PVA-H2SO4 acting as a solid-state electrolytic layer, over a range of −2.0 V to 2.0 V, at a scan rate of 25 mVs−1 and is depicted in Fig. 4A. The voltammogram provides a general analysis of the capacitive properties of the 3D-SC, in that the volume of the curve is indicative of the capacitance of the system. Herein, we visualise the curve intersect the zeroth potential line at ~±5.0 μA, indicating the charging current range available for the device. Next, the 3D-SCs capacitive performance was characterised via galvanostatic charge/discharge cycling over 200 cycles, and is described in terms of specific capacitance of the weight of the entire device, , the weight of the working electrode, , and the weight of the active material, graphene, in the working electrode, . The characteristic saw-tooth charge-discharge behaviours are shown in Fig. 4B, for the 3D-SC with a charging current of 5.0 μA. The 3D-SCs exhibit consistent behaviour over the 200 cycles without any notable variation in the shape or range, consistently showing the same change in gradient over the potential range 0–0.25 V. Given the nature of the saw-tooth wave determining the gradient and hence capacitive properties of the material is complex. Therefore, a technique highlighted by Kampouris et al.28 is utilised to reduce any ambiguity of any values presented in Fig. 4C. Figure 4
Cyclic voltammetry (A) of the 3D-SC consisting of a 2 mm layer of solid electrolyte of PVA and 1.0 M H2SO4. Corresponding charge/discharge curves with (C) and without (B) the Kampouris’ circuit in parallel are also presented. Scan Rate: 25 mV s−1. Inset to A is a schematic of the 3D-SC utilised throughout this study. Full size image
Attention was next turned towards obtaining the specific capacitance (CS) values of the 3D-SCs. Current literature utilises an array of methods in the calculation of CS, however the differences observed for each method are not reported. Thus, in this work a diverse range of methods were utilised to calculate the CS values and Table 4 exhibits the differences observed. Method 1 is the typical analysis of entire device; method 2 evaluates the specific capacitance of the working electrode only; and method 3 indicates the specific capacitance associated with the active material only. In these equations, CObs is the observed capacitance (F) of the entire device. Furthermore, mDevice is the mass (g) of the entire device, both electrodes and the mass of the solid electrolyte layer. Also mWE is the mass of the working electrode only and mAct is the mass of the active material in the working electrode i.e. graphene, assumed to be 8% of the total working electrode: Table 4: Comparison of capacitance and specific capacity for the 3D-SC over the range of applied currents (0.5–200 μA), calculated for the whole device, the working electrode (WE) and the active material within the printed 3DE (i.e. 8% graphene). Full size table
Method 1 for determining the capacitance of the device:
Method 2 for determining the capacitance of the working electrode:
Method 3 for determining the capacitance of the active material: Table 4 exhibits specific capacity values for the whole device, working electrode and total active material (i.e. loading of 8% of total wt. confirmed by TGA), it is clear that the values, although not competitive with advanced nanomaterials, demonstrate the capabilities and potential for the fabrication of low cost, non-toxic 3D supercapacitative architectures.
, the weight of the working electrode,
, and the weight of the active material, graphene, in the working electrode,
. The characteristic saw-tooth charge-discharge behaviours are shown in Fig. 4B, for the 3D-SC with a charging current of 5.0 μA. The 3D-SCs exhibit consistent behaviour over the 200 cycles without any notable variation in the shape or range, consistently showing the same change in gradient over the potential range 0–0.25 V. Given the nature of the saw-tooth wave determining the gradient and hence capacitive properties of the material is complex. Therefore, a technique highlighted by Kampouris et al.28 is utilised to reduce any ambiguity of any values presented in Fig. 4C.
(20min delay)