Electrochemical Detection of Piezoelectric Effect from Misaligned Zinc Oxide Nanowires Grown on a Flexible Electrode

The piezoelectric effect from a packed layer of zinc oxide nanowires (ZnO NWs) can be used in an electrochemical device for energy harvesting. In this work, ZnO NWs have been synthesized on flexible conductive electrodes using the hydrothermal growth method under solution agitation. The scanning electron microscopy (SEM) images show poor alignment of NWs which is assumed to be the key issue for generating piezoelectric effect by bending the substrate. The piezoelectric effect of the grown NWs has been investigated in an electrochemical cell containing an electrochemically active redox material. A reversible voltage shift up to 316 mV has been measured for the redox potential in the cell by bending the electrode. Using cyclic voltammetry (CV) method, the piezoelectric effect has been studied in different samples with various NWs length under different bending curvatures. It is found that the piezo effect is more pronounced in samples with longer NWs. Also, the electrochemical impedance spectroscopy (EIS) of a sample under bending and straight conditions shows that the piezo effect can change the depletion width in the NWs. The feasibility of using ZnO NW for mechanical energy harvesting has been demonstrated in a supercapacitor device.