A microwave irradiation method has been used to prepare mixed nickel cobalt sulfide (NixCoyS4) nanosheets with different stoichiometric composition as electrodes for electrochemical capacitors. This study has been undertaken to determine the effect of synthesis time and concentration of nickel on the morphology and pseudocapacitance behavior of the NixCoyS4. It was observed that the time had an effect on the morphology of NixCoyS4, producing sheet-like (leaf-like) morphology which curls in flower-like shapes with increase in growth (synthesis) time. The effect of morphology on the electrochemical behavior was studied by cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) techniques in aqueous solutions. The sample with a concentration ratio of 2:1 of nickel and cobalt (NixCoyS4-(3)) shows higher faradaic performance when compared to other samples grown under similar conditions but with different ratios. The maximum specific capacitance values obtained for was 1110 Fg(-1) at a scan rate of 5 mV s(-1) for this sample. The Coulombic efficiency of the sample was similar to 80% after 2000 galvanostatic charge-discharge cycles at a current density of 5A g(-1). Crown Copyright (C) 2015 Published by Elsevier Ltd. All rights reserved.