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Two kinds of electrode materials were produced to fabricate asymmetric supercapacitor devices: (i) Highly defective, n-type wide bandgap semiconductor ZnO nanocrystalline electrodes below 50 nm were synthesized with the aid of the high energy ball milling technique. (ii) Flexible 3D-graphene foams were synthesized via the chemical vapor deposition technique. Extensive defect structure analysis was performed via enhanced characterization techniques mainly the spectroscopy ones: electron paramagnetic resonance (EPR), Raman, and photoluminescence (PL). Compared to bulk ZnO electrodes the nanoscale ZnO electrodes revealed a dramatic increase of defect concentration. The surface defect plays a crucial role in the electrochemical performance of supercapacitor devices. Strong decreases in charge transfer resistance were observed for the smallest crystallite size which is 15 nm. This work also shows …