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.