Novel cellulose-derived hybrid carbon nanofibre (CNF)/carbon nanotubes (CNTs) electrode-based structural supercapacitors, combined with a solid electrolyte, have been produced. Galvanostatic charge/discharge and electrochemical impedance spectroscopy measurements were used to assess the electrodes' performance. The CNF/CNTs electrodes have a better capacitive performance than the plain CNF electrodes; 0.91 +/- 0.02 and 3.35 +/- 0.05 mF cm(-2) for CNF and CNF/CNTs, respectively. A Raman spectroscopic approach was used to investigate the stress transfer properties of the CNF within a poly(methyl methacrylate) (PMMA) resin matrix. Deformation of the carbon structures was observed via shifts towards a lower wavenumber position of the G band (similar to 1590 cm(-1)) for CNF and CNF/CNTs samples processed at a carbonization temperature of 2000 degrees C. Moduli of these fibres were estimated to be similar to 145 and similar to 271 GPa, respectively, suggesting the growth of CNTs not only enhances the capacitive performance but also the mechanical performance of the structural supercapacitors.