Unexpected properties of gallium incorporated nickel oxide for electrochemical energy storage

With the aim of tailoring the electrochemical properties of p-type nickel oxide, the logical approach is to dope the material with a p-type acceptor to improve both the conductivity and supercapacitor performance. However, in this work, we incorporated an n-type element into p-type NiO instead. This is for examining such effect that is poorly known. Group III redox-inactive element Ga is chosen to be incorporated into NiO to investigate the effect on the crystal structure, morphology and supercapacitor performance. The results demonstrate that Ga incorporated nickel oxides have the same crystal structures as that of un-doped NiO. Unsurprisingly, specific capacitance decreases after doping Ga in small amounts. However, it is counter-intuitive that the capacitance increases with a further increase in the content of Ga in the nickel oxide. From the studies, maximum capacitance much higher than that of the un-doped NiO is achieved when the atomic ratio of gallium is 7 percent in the precursor solution. The expected and unexpected results are analyzed and discussed. (C) 2016 Elsevier Ltd. All rights reserved.