Enhanced capacity and electrochemical performance of zinc cobalt selenide by using a novel two-stage synthesis method

In this paper, a novel method of synthesis of zinc cobalt selenide (ZnCoSe) nanostructures via the hydrothermal method is introduced that is comprised of two stages as opposed to the direct method that could be done in a single stage. In the single-stage method, the consequent electrodes were covered by ZnCoSe that was directly and immediately synthesized while in the two-stage method, first, zinc cobalt oxide (ZnCoO) was hydrothermally produced then the oxygen atoms were replaced by selenium and the ZnCoSe* electrode was indirectly obtained. The structural and electrochemical evaluations showed boosted performance of the ZnCoSe* whose structure was found to be nanowire. In this paper, the specific capacitance values (Csp) of the ZnCoSe* , ZnCoO and ZnCoSe electrodes were measured to be 104, 64 and 62 F.g-1 at 20 mV/s scan-rate by Cyclic voltammetry (CV) which alongside the Galvanostatic Charge-Discharge (GCD) analysis, led us to conclude superior activity of the ZnCoSe* electrode. Electrochemical impedance spectroscopy (EIS) was also performed and its results were in accordance with those of the cyclic voltammetry. Based on the EIS results, ZnCoSe* showed the smallest charge transfer resistance (6.5 ohm/cm-2)  and consequently the supreme electrochemical behavior among the studied electrodes. Moreover, a better capacity retention value was recorded in the cyclability test of the ZnCoSe* electrode as the specific capacity value of this electrode reached 145% of its initial value after 2000 cycles.