Enhancing the electrochemical performance of graphene supercapacitors by coating their electrodes with a slurry-paste of ZnO:Al, ZnO:Ga and ZnO: In

This investigation reports the morphological and structural properties of ZnO doped with the Al, In and Ga el-ements and its utilization as redox material to improve the capacitance and energy density of graphene super -capacitors (SCs). All the ZnO nanoparticles doped with these elements presented a plate-like morphology with irregular edges and had hexagonal wurtzite phase. Moreover, the values of band gap were obtained for the ZnO nanoparticles and they are reduced with the order of: ZnO:Ga (3.2 eV)> ZnO:In (3.0 eV)> ZnO:Al (2.95 eV). The results of electrochemical characterization revealed that the graphene SCs made without ZnO presented a maximum capacitance and energy density of 97.2 F g-1 and 19.4 Wh kg-1, respectively. After the deposition of the Al, In or Ga-doped ZnO nanoparticles to the SC electrodes, the capacitance and energy density are enhanced by 22-193%. The maximum values of capacitance and energy density of 284.6 F g-1 and 56.9 Wh kg-1 were observed for the SC made with ZnO:Al. Moreover, the analysis by Raman and photoluminescence demonstrated the presence of Zinc interstitials, oxygen vacancy and oxygen interstitials defects, which served as redox centers for the charge storage in the solid state SCs. In general, this research confirmed that adding doped ZnO into the SCs is a good strategy to increment their performance, which is of interest for energy storage applications.