Flexible Co(OH)2/NiOxHy@Ni hybrid electrodes for high energy density supercapacitors

It is a great challenge to develop a new kind of electrode materials simultaneously possessing the high energy density as well as good flexibility for high performance wearable supercapacitors. Herein, a flexible bimetallic electrode with novel interconnected hierarchically porous network, i.e. ultrathin Co(OH)2 nanopetals deposited on nanoporous nickel oxide/[email protected] [email protected] structure (Co(OH)2/np-NiOxHy@Ni), is synthesized through dealloying and electrodeposition. The hierarchical porous structure provides high effective surface area to reserve electrolytes and facilitates ions diffusion, which significantly improves the reaction kinetics of the active materials. Owing to the hierarchical porous structure and synergetic effect of Co(OH)2 and NiOxHy electroactive materials, the Co(OH)2/np-NiOxHy@Ni hybrid electrode delivers wider voltage window (–0.1~0.6 V) and higher specific capacitance (1421.1F cm−3 at 0.5 A cm−3) than the single transition-metal electrodes. Density functional theory (DFT) further proves that the d-orbit of Co atom in Co(OH)2 and the p-orbit of O atom in NiO forms a strong hybridization, which endows the newly developed Co(OH)2/np-NiOxHy@Ni electrode an improved electrochemical performance. Furthermore, the flexible all-solid-state symmetric supercapacitors (SCs) is assembled using Co(OH)2/np-NiOxHy@Ni hybrid electrode. The SCs deliver a high energy density of 59.2 mWh cm−3, which far excels those of commercial supercapacitors (less than10 mWh cm−3). Moreover, the watch could run for more than 45 min while the SCs is subjected with different deformations, demonstrating a fascinating application prospects in the wearable fields.