Hierarchical Architectured Dahlia Flower-Like NiCo2O4/NiCoSe2 as a Bifunctional Electrode for High-Energy Supercapacitor and Methanol Fuel Cell Application

We report unique hierarchical dahlia flower-like NiCo2O4 nanograss/NiCoSe2 nanosheets on Ni foam (NCO/NCS/NF) as bifunctional binder-free electrodes for high energy density hybrid supercapacitors and methanol electro-oxidation applications. NCO/ NCS/NF is synthesized by a facile hydrothermal method followed by an electrodeposition process. As a supercapacitor electrode, NCO/NCS/NF exhibits a superior specific capacitance of 2045.5 F g(-1) (227 mAh g(-1) or 818 C g(-1)) at 1.8 A g(-1). The assembly of a hybrid NCO/ NCS/NF//AC device delivers impressive specific energy of 54.5 Wh kg(-1) at 350 W kg(-1) with durable cyclic stability of 82.5% after 10,000 charge-discharge cycles. NCO/NCS/NF as an electrocatalyst toward methanol oxidation yields a high current density of 130 mA cm(-2) at 0.5 V and a low onset potential of 0.13 V, in comparison to other reported catalysts. Such high electrochemical performance of a binder-free NCO/NCS/NF electrode is attributed to the synergistic effect between the bimetallic oxides and selenides, core-shell nanostructure, hierarchically aligned architectures of nanograss/nanosheets, and conductive coatings of NCS to provide rapid charge transfer reactions. To the best of author's knowledge, this is the first report of a 3D hierarchical NCO/NCS/NF 1D/2D nanostructure toward a bifunctional binder-free electrode for energy storage and conversion technologies.