2, 6-Diaminopyridine decorated reduced graphene oxide as integrated electrode with excellent electrochemical properties for aqueous supercapacitors

Asymmetric Supercapacitors based on 1,10-phenanthroline-5,6-dione Molecular Electrodes Paired with MXene

An efficient approach to increase the energy density of supercapacitors is to prepare electrode materials with larger specific capacitance and increase the potential difference between the positive and negative electrodes in the device. Herein, an organic molecular electrode (OME) is prepared by anchoring 1,10-phenanthroline-5,6-dione (PD), which possesses two pyridine rings and an electron-deficient conjugated system, onto reduced graphene oxide (rGO). Because of the electron-deficient conjugated structure of PD molecule, PD/rGOs exhibit a more positive redox peak potential along with the advantages of high capacitance-controlled behaviour and fast reaction kinetics. Additionally, the small energy gap between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) leads to increased conductivity in PD/rGO. To assemble the asymmetric supercapacitor (ASC), a two-dimensional metal carbide, as known as MXene, with a chemical composition of Ti3C2Tx is selected as the negative electrode due to its exceptional performance, and PD/rGO-0.5 is employed as the positive electrode. Consequently, the working voltage is expanded up to 1.8 V. Through further electrochemical measurements, the assembled ASC (PD/rGO-0.5//Ti3C2Tx) achieves a remarkable energy density of 36.8 Wh kg-1. Remarkably, connecting two ASCs in series can power 73 LEDs, showcasing its promising potential for energy storage applications.

Free-standing reduced graphene oxide/carboxymethylcellulose-polyaniline (RGO/CMC-PANI) hybrid film electrode for high-performance asymmetric supercapacitor device

This work demonstrates a facile and effective strategy for the preparation of a reduced graphene oxide/carboxymethylcellulose-polyaniline (RGO/CMC-PANI) hybrid film electrode. Specifically, through the hydrogen bonding interaction between -OH of CMC molecules and -NH₂ of aniline monomer, PANI grows in an ordered manner on the surface of CMC, which effectively alleviates the structural collapse of PANI during the continuous charge/discharge process. After compounding with RGO, CMC-PANI bridges adjacent RGO sheets to form a complete conductive path, and opens the gap between RGO sheet layers to obtain fast ion channels. As a result, the RGO/CMC-PANI electrode exhibits excellent electrochemical performance. Moreover, an asymmetric supercapacitor was fabricated using RGO/CMC-PANI as the anode and Ti₃C₂T_x as the cathode. The results show that the device has a large specific capacitance of 450 mF cm^-2 (81.8 F g^-1) at 1 mA cm^-2 and a high energy density of 140.6 μWh cm^-2 at a power density of 749.9 μW cm^-2. Besides, 87.3 % initial capacitance and 100 % good coulombic efficiency can be maintained even after 20,000 GCD cycles. Therefore, the device has a broad application prospect in the field of new-generation microelectronic energy storage.

Organic Small-Molecule Electrodes: Emerging Organic Composite Materials in Supercapacitors for Efficient Energy Storage

Organic small molecules with electrochemically active and reversible redox groups are excellent candidates for energy storage systems due to their abundant natural origin and design flexibility. However, their practical application is generally limited by inherent electrical insulating properties and high solubility. To achieve both high energy density and power density, organic small molecules are usually immobilized on the surface of a carbon substrate with a high specific surface area and excellent electrical conductivity through non-covalent interactions or chemical bonds. The resulting composite materials are called organic small-molecule electrodes (OMEs). The redox reaction of OMEs occurs near the surface with fast kinetic and higher utilization compared to storing charge through diffusion-limited Faraday reactions. In the past decade, our research group has developed a large number of novel OMEs with different connections or molecular skeletons. This paper introduces the latest development of OMEs for efficient energy storage. Furthermore, we focus on the design motivation, structural advantages, charge storage mechanism, and various electrode parameters of OMEs. With small organic molecules as the active center, OMEs can significantly improve the energy density at low molecular weight through proton-coupled electron transfer, which is not limited by lattice size. Finally, we outline possible trends in the rational design of OMEs toward high-performance supercapacitors.