Microstructural and electrochemical supercapacitive properties of Cr‐doped CuO thin films: Effect of substrate temperature

Abstract

Transition metal oxides have attracted a special interest in the applications of energy storage and conversion devices because of their distinctive structural, electronic, and catalytic properties. In the current study, the effect of substrate temperature on binder-free undoped CuO and Cr-doped CuO (~4.5 at. %) thin-film electrodes prepared by radio frequency sputtering technique is reported for supercapacitor applications. X-ray diffraction studies revealed the formation of undoped CuO and Cr-doped CuO films with monoclinic structure, while field emission scanning electron microscopy showed a significant change in the shape and size of the grains as a function of the substrate temperature. X-ray mapping indicated a uniform distribution of the elements present in these films. Substitution of Cr of ~4.5 at. % has not altered the primary monoclinic structure of CuO, but the doped CuO thin-film electrodes showed an improved conductivity. The electrochemical supercapacitive performance of the thin-film electrodes was studied using cyclic voltammetry, galvanostatic cycling with potential limitation, and electrochemical impedance spectroscopy techniques in 1 M KOH. The electrochemical measurements revealed that the thin-film electrode of Cr-doped CuO electrode developed at the substrate temperature of 573 K exhibited the highest areal capacitance of 209 mF cm−2 at a scan speed of 10 mV s−1, which is five times higher than that of the pure CuO (38 mF cm−2) thin-film. Furthermore, the Cr-doped CuO thin-film electrode exhibited excellent cycling stability with the capacity retention of 88% for 3000 continuous CV cycles in 1 M KOH. These results suggested that the binder-free Cr-doped CuO film electrodes prepared at the substrate temperature of 573 K is an excellent candidate material for the supercapacitor applications.