Strategies to enhance the electrochemical performance of strontium-based electrode materials for battery-supercapacitor applications

Hollow Ni3S4@Co3S4 with core-satellite nanostructure derived from metal-organic framework (MOF)-on-MOF hybrids as an electrode material for supercapacitors

Metal-organic frameworks (MOFs) have found wide applications in the field of supercapacitors due to their highly controllable porous structure, big specific surface area, and abundant chemical functional groups. MOF-on-MOF hybrids not only enhance the composition of MOFs (such as ligands and/or metal centers) but also provide greater structural diversity. By utilizing MOFs as precursors for preparing sulfides, the unique characteristics and inherent structure of MOFs are preserved but their conductivity and capacitance are enhanced. This study successfully synthesized hollow-structured Ni3S4@Co3S4 derived from an Ni-MOF@ZIF-67 hybrid structure, where the Ni-MOF serves as the core and ZIF-67 as the satellite. The Ni3S4@Co3S4 electrode demonstrated a specific capacity as high as 747.3 C g-1 at 1 A g-1, and it could still maintain 77% of its initial capacity at 10 A g-1. Furthermore, the assembled Ni3S4@Co3S4//AC hybrid supercapacitor (HSC) device achieved a maximum energy density of 30.8 W h kg-1 when the power density was 750 W kg-1. The device exhibited remarkable cycling durability, retaining 85.4% of its initial capacitance after 5000 cycles. Therefore, the derived functional materials based on MOF-on-MOF provide a more scalable and promising approach for the preparation of efficient electrode materials.

Supercapatteries as Hybrid Electrochemical Energy Storage Devices: Current Status and Future Prospects

Among electrochemical energy storage (EES) technologies, rechargeable batteries (RBs) and supercapacitors (SCs) are the two most desired candidates for powering a range of electrical and electronic devices. The RB operates on Faradaic processes, whereas the underlying mechanisms of SCs vary, as non-Faradaic in electrical double-layer capacitors (EDLCs), Faradaic at the surface of the electrodes in pseudo-capacitors (PCs), and a combination of both non-Faradaic and Faradaic in hybrid supercapacitors (HSCs). EDLCs offer high power density but low energy density. HSCs take advantage of the Faradaic process without compromising their capacitive nature. Unlike batteries, supercapacitors provide high power density and numerous charge-discharge cycles; however, their energy density lags that of batteries. Supercapatteries, a generic term that refers to hybrid EES devices that combine the merits of EDLCs and RBs, have emerged, bridging the gap between SCs and RBs. There are numerous articles and reviews on EES, and many of those articles have emphasized various aspects of HSCs and supercapatteries. However, there are no recent reviews that dealt with supercapatteries in general. Here, we review recently published critically selected articles on supercapatteries. The review discusses different EES devices and how supercapatteries are different from others. Also discussed are properties, design strategies, and future perspectives on supercapatteries.

Tailoring the interfacial surfaces of tungsten and molybdenum tungsten disulfide electrodes for hybrid supercapacitors

The layered structures of tungsten disulfide (WS₂) and molybdenum tungsten disulfide (MoWS₂) are considered as the most promising electrode materials for energy storage devices. Herein, MS (magnetron sputtering) is required for the deposition of WS₂ and MoWS₂ on the surface of the current collector to attain an optimized layer thickness. The structural morphology and topological behavior of the sputtered material were examined via X-ray diffraction and atomic force microscopy. Three-electrode assembly was used to start the electrochemical investigations to identify the most optimal and effective sample among WS₂ and MoWS₂. CV (cyclic voltammetry), GCD (galvanostatic charging discharging), and EIS (electro-impedance spectroscopy) techniques were employed to analyze the samples. After preparing WS₂ with optimized thickness as the superior performing sample, a hybrid device was designed as WS₂//AC (activated carbon). With a remarkable cyclic stability of 97% after 3000 continuous cycles, the hybrid supercapacitor generated a maximum energy density (E_s) value of 42.5 W h kg^-1 and 4250 W kg^-1 of power density (P_s). Besides, the capacitive and diffusive contribution during the charge-discharge process and b-values were calculated by Dunn's model, which lay in the 0.5-1.0 range and the fabricated WS₂ hybrid device was found to have a hybrid nature. The outstanding outcomes of WS₂//AC make it suitable for future energy storage applications.

Exploring MOF-199 composites as redox-active materials for hybrid battery-supercapacitor devices

Metal-organic frameworks (MOFs) have emerged as intriguing porous materials with diverse potential applications. Herein, we synthesized a copper-based MOF (MOF-199) and investigated its use in energy storage applications. Methods were adapted to intensify the electrochemical characteristics of MOF-199 by preparing composites with graphene and polyaniline (PANI). The specific capacity of the synthesized MOF in a three-electrode assembly was significantly enhanced from 88 C g^-1 to 475 C g^-1 and 766 C g^-1 with the addition of graphene and polyaniline (PANI), respectively. Due to the superior performance of (MOF-199)/PANI, a hybrid supercapacitor was fabricated with the structure of (MOF-199)/PANI//activated carbon, which displayed an excellent maximum energy and power density of 64 W h kg^-1 and 7200 W kg^-1, respectively. The hybrid device exhibited an appreciable capacity retention of 92% after 1000 charge-discharge cycles. Moreover, using Dunn's model, the capacitive and diffusive contributions as well as the k ₁ and k ₂ currents of the fabricated device were calculated, validating the hybrid nature of the supercapattery device. The current studies showed that MOF-199 exhibits promising electrochemical features and can be considered as potential electrode material for hybrid energy storage devices.