High supercapacitive performance of sol–gel ZnO-doped manganese oxide coatings

In the present study, ZnO-doped manganese (Mn) oxide coatings were prepared as a function of ZnO content (≤40at.%) by sol–gel process. After post heat treatment at 300°C, the influences of ZnO on the microstructural characteristics and pseudocapacitive performance of the Mn-oxide films were investigated. The structural analyses identified the sol–gel ZnO-doped Mn-oxide powder as a tetragonal Mn3O4 phase with a nanocrystalline structure. The formation of ZnxMn3−xO4 spinel occurred when ZnO content was ≥20at.%. The crystallite size of Mn-oxide powder increased when a small amount of ZnO was added, and then decreased when larger amounts were added. The cyclic voltammetry (CV) data showed that the specific capacitance (SC) of the Mn-oxide film in 1M Na2SO4 electrolyte can be increased from 236F/g to 301F/g at 25mV/s by doping with 10at.% ZnO. The formation of spinel tended to inhibit the SC value of the films. After activation of the Mn-oxide film, however, a relatively high cycling efficiency of >85% was obtained for all compositions after 1200 CV cycles. ► ZnO doping does increase the pseudocapacitive performance of sol–gel Mn-oxide. ► The Mn/Zn-oxide was identified as Zn–Mn spinel when ≥20at.% ZnO was added. ► A maximum improvement of ~28% in capacitance can be obtained by doping ZnO. ► The coating exhibited ability without influence of smoothening mechanism after CV. ► ZnO doping can improve the cycling stability up to an efficiency higher than 85%.