Influence of Cu doping on structural, optical and electrochemical performance of spray pyrolyzed Cu doped Co3O4/FTO thin film electrodes

This study uses the spray pyrolysis technique to prepare pure and different content (2 at%, 4 at%, 6 at%, and 10 at%) of Cu-doped Co3O4/FTO thin films. The structural and optical properties of the synthesized thin films were further characterized using X-ray diffraction, field emission scanning electron microscope, energy dispersive X-ray analyzer, elemental mapping and UV-Vis spectroscopy. The addition of Cu not only changed the crystal structure, crystalline size, surface morphology and band gap of Cu-doped Co3O4/FTO thin films but also impacted the surface area and defects in Co3O4, affecting its electrochemical performance. The electrochemical results of the electrodes offer acceptable insights which confirming the battery-like behavior of Cu-doped Co3O4 thin films deposited on the FTO electrodes. The highest value of areal capacitance (6.77 mF/cm(2)) and the lowest values of charge transfer resistance (4.06 ohm.cm(2)) and equivalent distribution resistance (6.04 ohm.cm(2)) were corresponded to the 4 at% Cu-Co3O4/FTO thin film electrode. This is while the values of areal capacitance, charge transfer resistance and equivalent distribution resistance for undoped sample were (3.57 mF/cm(2)), (4.42 ohm.cm(2)) and (24.56 ohm.cm(2)), respectively. The obtained results of the electrodes suggested an enhance in conductivity, areal capacitance and charge storage capability for the Cu-Co3O4/FTO thin film electrode with Cu doping content of 4 at% because of the smaller crystallite size, better ion diffusion, decrease of voltage drop and increase of active sites on the surface of this electrode.