## 3 Results and Discussion
The electrochemical performance of the printed MWCNTs/AC/BNNTs composite was studied in detailed in a three-electrode system and the relevant results are illustrated in Figure 5. The added different contents (0, 0.25, 0.50, 0.75 and 1 wt.%) of the BNNTs in MWCNTs/AC are marked by the given series of MWCNTs/AC-1, MWCNTs/AC/BNNTs-2, MWCNTs/AC/BNNTs-3, MWCNTs/AC/BNNTs-4 and MWCNTs/AC/BNNTs-5 composite materials, respectively. We can observe that the printed MWCNTs/AC/BNNTs-3 composite electrode material has shown high electrochemical performance in terms of both the cyclic-voltammetry (CV) and GCD outputs. A possible reason for the improved electrochemical performance of MWCNTs/AC/BNNTs-3 is that the addition of the optimal BNNTs content weakened the agglomeration phenomena of the AC particles and MWCNTs in the composite electrode material. In addition, BNNTs are very stable in acidic as well as in basic aqueous electrolytes and also the presence of BNNTs increase the electrolyte uptake. The reduced agglomeration phenomena of the MWCNTs/AC/BNNTs-3 composite electrode material may have resulted possibly in the improved surface area and maximum access to the electrolyte solution in the electroactive multicomponent system [14]. Another possible reason for the improved electrochemical properties of the MWCNTs/AC/BNNTs-3 composite electrode material is that the printed multicomponent system allows each component to participate with a synergistic effect to boost its electrochemical performance. However, MWCNTs/AC-1, MWCNTs/AC/BNNTs-2, MWCNTs/AC/BNNTs-4 and MWCNTs/AC/BNNTs-5 have shown inferior electrochemical performance in comparison to the MWCNTs/AC/BNNTs-3 composite material, owing to insufficient and overdoses of the BNNT contents in the composite electrode material, respectively. Once the optimization stage was fully investigated, the electrochemical performance of the optimized printed MWCNTs/AC/BNNTs-3 composite electrode material was studied in detail (Figure 5). Figure 4: (**a**,**b**) The typical XRD and Raman analyses of the MWCNTs/AC/BNNTs ternary composite material, respectively. (**c**–**e**) N\({}_{2}\) adsorption–desorption isotherms (inset show pore size distribution) of the MWCNTs, activated carbon and BNNTs, respectively. The CV response of the printed MWCNTs/AC/BNNTs-3 composite electrode material was investigated thoroughly at various scan rates (Figure 6a). The current density of the composite electrode material increased with an increasing scan rate, ranging from lower to maximum values of 5 to 100 mV s\({}^{-1}\). Similarly, the electrochemical performance of the printed MWCNTs/AC/BNNTs-3 composite electrode material in terms of the GCD was also measured, and the recorded results are depicted in Figure 6b. The MWCNTs/AC/BNNTs-3 composite has shown a lengthy charging-discharging cycle at a minimum current density of 1 A g\({}^{-1}\), while the charging-discharging cycle lengths were decreased as the current density was increased from 1 to 10 A g\({}^{-1}\). The specific capacitance of the MWCNTs/AC/BNNTs-3 composite electrode material was calculated from the measured GCD plots according to Equation (1). The MWCNTs/AC/BNNTs-3 composite has shown a maximum specific capacitance of 262 F g\({}^{-1}\) at 1 A g\({}^{-1}\) with 49.61% capacitance retention at a maximum current density of 10 A g\({}^{-1}\). In addition, the charge transfer and solution resistance kinetics were studied by EIS and the measured results are displayed in Figure 6d. The as-fabricated MWCNTs/AC/BNNTs-3 composite has shown a minimum charge transfer resistance (R\({}_{\text{ct}}\)) of 0.15 \(\Omega\) due to the presence of multiple carbon-based elements, such as AC and MWCNTs. Moreover, the stability testing of the printed MWCNTs/AC/BNNTs-3 composite film was also evaluated (Figure 6e) and it demonstrated a specific capacitance retention of 95% after the maximum number of cycles (1000).