Electrodeposition of CoSx-graphene nanoplatelets on Ni(OH)2 nanosheets for improving the pseudocapacitance performance

Abstract

In the present work, binder-free CoSx–graphene nanoplatelets porous structures were coated on Ni(OH)2 nanosheets using a one-step electrodeposition process. The graphene was produced from the electroreduction of CO2∗ intermediates during the electrodeposition of CoSx. The surface morphology and interfacial bonding states of CoSx–graphene@Ni(OH)2 were sensitive to the deposition time and Co–to–thiourea molar ratio (Mr). The interface reconstruction between CoSx–graphene NCs and Ni(OH)2 nanosheets improved the pseudocapacitance performance, which was investigated at different Mr and varying deposition times. Raman spectra verified the presence of graphene and CoSx mixed phases in all heterostructure electrodes, where CoS2 was dominant at Mr = 0.2. An XPS analysis indicated the evolution of various interfacial bonding states (CO, CO, CoONi, and SO) between Ni(OH)2 nanosheets and CoSx-graphene nanoplatelets, revealing the improvement in the interfacial synergy and concentration of electroactive sites. The hybrid CoSx-graphene@Ni(OH)2 NCs at Mr = 0.2 exhibited the highest capacitance of 2116 F∙g−1 at 2 mV∙s−1 and 1618 F∙g−1 at 1 A∙g−1 compared with bare Ni(OH)2, which achieved 1212 F∙g−1 at 2 mV∙s−1 and 882.88 F∙g−1 at 1 A∙g−1, and other NCs. Bare Ni(OH)2 nanosheets retained only capacitance retention of 25 % after 2000 cycles, which improved to 70 % in all CoSx-graphene@Ni(OH)2 nanoplatelets.