2022, Ramadoss, Ananthakumar, Mohanty, Ankita, Saravanan, K. Gobi, Kundu, Manab, Noby, Sohaila Z., Kirubavathi, K., Selvaraju, K., Schmidt-Mende, Lukas

The energy storage devices for flexible/wearable and portable electronics are on immediate requirement demanding for high-performance flexible supercapacitors. Nevertheless, the real-time application of advanced electronics necessitates supercapacitors to own admirable mechanical properties to endure rigorous straining environments. Also, it is necessary to reduce the mass and volume of the whole device. Therefore, constructing a high-performance flexible supercapacitor based on better electrochemical and significant mechanical properties is still a formidable task. Herein, we have successfully fabricated a vanadium nitride thin film electrode onto the flexible, thin, and light-weight graphite paper substrate via reactive direct current (DC) magnetron sputtering method. The as-fabricated graphite sheets current collector is flexible, thin, light-weight, electrically conductiviting, cost-effective, and easy to fabricate. Furthermore, the as-prepared binder-free flexible negative electrode displayed better supercapacitor performance in terms of specific capacitance and cycle stability. The negative electrode exhibited an areal capacitance of 91 mF cm⁻² and better cycling stability with > 64% capacitance retention after 2000 cycles. Moreover, the flexible hybrid supercapacitor is fabricated with NiCo hydroxide and VN films and showed a maximum energy density of 1.80 μWh cm⁻² and power density of 387.5 μW cm⁻² and good stability. These results propose that the fabricated electrode has great prospective as a power source for flexible, wearable, and portable electronic devices.

2021, Mohanty, Ankita, Jaihindh, Dhayanantha Prabu, Fu, Yen-Pei, Senanayak, Satyaprasad P., Schmidt-Mende, Lukas, Ramadoss, Ananthakumar

Metal-organic frameworks (MOFs) are evolving as emerging materials for application in supercapacitors on account of their inherent porous characteristics, which can be suitably controlled with molecular engineering. This allows suitable attributes to MOFs such as multiple dimensionalities, high surface area and additional aspect ratio compared to traditional materials. Secondary building units (SBUs) are the milestones that allow immense structural diversity, thermodynamic stability, and mechanical/architectural stability to demonstrate materials on-demand with predetermined topologies in the synthesis of MOFs through stronger bonding between the constituent metals and organic linkers. Despite these advancements, the usage of pristine MOFs is lagging in the area of supercapacitor, majorly due to their insulating nature. As smart avenues, hybridization of MOFs or using MOFs as templates for deriving metal oxide, carbon or hydroxides etc., are being proved as hugely successful. This review is directed towards the utilization of MOFs, specifically three-dimensional MOFs as a platform for utilization in supercapacitor. Extensive discussion is developed on divergent methods related to the synthesis of MOFs, their performance in supercapacitor application and various strategies adopted to enhance their functionality. Finally, the future prospective and possible research proceedings in this field are described briefly.

2022, Ramadoss, Ananthakumar, Wong, Ka Kan, Swain, Nilimapriyadarsini, Mohanty, Ankita, Kirubavathi, K., Selvaraju, K., Schmidt-Mende, Lukas

In the present work, we have introduced lightweight, ultrabendable, rough graphite sheets on a polyimide tape substrate as a current collector. The flexible current collector was fabricated by the peel-off method. The as-prepared graphite-sheet-coated polyimide substrate is ultraflexible (bendable, rollable, and twistable), thin, and lightweight, has better conductivity, high mechanical durability, and ease of fabrication, and is cost-effective, rough, and environment friendly. The fabricated flexible current collector could be directly used as the substrate for constructing RuO₂–MnO₂/graphite flexible supercapacitors. The as-prepared electrode delivered a maximum gravimetric capacitance of 183 F g^–1 (73.5 mF cm^–2) at a current density of 1 A g^–1 with better rate capability and 96% capacitance retention (after 5000 cycles). The better electrochemical performance of the electrode is due to the rough surface and good electrical conductivity of the current collector leads to the better attachment of active material and rapid ions/electron transfer.

2022, Noby, Sohaila Z., Mohanty, Ankita, Zirak, Peyman, Ramadoss, Ananthakumar, Schmidt-Mende, Lukas

Molybdenum oxide (MoO₃) is an appropriate electrode material for vast applications such as gas sensing, catalyst, and energy storage devices. Its high oxidation states provide the possibility for ion intercalation and de-intercalation to the electrode material, which is truly advantageous for supercapacitor application. Herein, we report about reduced vertically aligned α-MoO₃ nanoblades on conducting substrates via a post-treatment in reduced gas environments (H₂, N₂ and vacuum) to tune their conductivity by introducing oxygen vacancies. These α-MoO₃ nanoblades were further carbonized through decomposition of glucose as a carbohydrate material to obtain binder-free carbon coated vertically aligned α-MoO₃ electrode. As a binder-free supercapacitor negative electrode, the vacuum treated α-MoO₃ electrode showed the highest specific capacitance (39.8 mF cm⁻²), as compared to that achieved by N₂ and H₂ treated samples (29.2 mF cm⁻² and 24.5 mF cm⁻², respectively). Besides, the vacuum annealed electrode also maintained around 76.4% of its initial specific capacitance value after 10,000 cycles indicating a more stable electrochemical performance of such electrode. An asymmetric device 3D-MnO₂//α-MoO₃ was assembled and it attained maximum specific capacitance value of 37.5 mF/cm² at current density value 1.5 mA cm^{− 2} and maximum energy density value of 16.875 µWh cm^-2 at power density value of 675 µW cm^-2. The results demonstrate that the proposed hybrid synthesis approach is very promising for preparation of binder-free materials for high-performance supercapacitors.