Facile Synthesis of MnO 2 /Ti 3 C 2 T x /CC as Positive Electrode of All‐Solid‐State Flexible Asymmetric Supercapacitor

Electrophoretic deposition of MXenes and their composites: Toward a scalable approach

Over the past decade, MXenes, a novel class of advanced 2D nanomaterials, have manifested as a prominent electrode material with diverse applications. Their unique layered structures, negative zeta potential, charge carrier mobility, mechanical properties, adjustable bandgap, hydrophilicity, metallic nature, and surface chemistry collectively contribute to the abundance of active redox sites on the surface and a reduction in the ion diffusion pathway. Despite such promising attributes of MXene, challenges like aggregation and restacking reduce the accessibility of active surface sites for electrolyte ions. Amongst approaches such as surface functionalization, addition of spacers, or facilitating pore formation, the electrophoretic deposition (EPD) of MXene on substrates has commenced to gain attention aiming to mitigate these issues. More importantly, it offers large-scale film fabrication in a short time without the necessity of using a charge-inducing agent. This review compiles recent advances in the use of EPD for preparing MXene-based electrodes and discusses the effect of EPD parameters on the relevant device performance. Recognition is given to understanding the relation of MXene colloidal composition in aqueous (and in some cases, non-aqueous) dispersions, deposition times, and other relevant parameters on respective device performances. In conclusion, the potential avenues offered by MXenes for future research on electrode materials are emphasized.

Electronic Structure Engineered Heteroatom Doped All Transition Metal Sulfide Carbon Confined Heterostructure for Extrinsic Pseudocapacitor

Ultra-high energy density battery-type materials are promising candidates for supercapacitors (SCs); however, slow ion kinetics and significant volume expansion remain major barriers to their practical applications. To address these issues, hierarchical lattice distorted α-/γ-MnS@Cox Sy core-shell heterostructure constrained in the sulphur (S), nitrogen (N) co-doped carbon (C) metal-organic frameworks (MOFs) derived nanosheets (α-/γ-MnS@Cox Sy @N, SC) have been developed. The coordination bonding among Cox Sy , and α-/γ-MnS nanoparticles at the interfaces and the π-π stacking interactions developed across α-/γ-MnS@Cox Sy and N, SC restrict volume expansion during cycling. Furthermore, the porous lattice distorted heteroatom-enriched nanosheets contain a sufficient number of active sites to allow for efficient electron transportation. Density functional theory (DFT) confirms the significant change in electronic states caused by heteroatom doping and the formation of core-shell structures, which provide more accessible species with excellent interlayer and interparticle conductivity, resulting in increased electrical conductivity. . The α-/γ-MnS@Cox Sy @N, SC electrode exhibits an excellent specific capacity of 277 mA hg-1 and cycling stability over 23 600 cycles. A quasi-solid-state flexible extrinsic pseudocapacitor (QFEPs) assembled using layer-by-layer deposited multi-walled carbon nanotube/Ti3 C2 TX nanocomposite negative electrode. QFEPs deliver specific energy of 64.8 Wh kg-1 (1.62 mWh cm-3 ) at a power of 933 W kg-1 and 92% capacitance retention over 5000 cycles.

Rational design of flower-like MnO2/Ti3C2Txcomposite electrode for high performance supercapacitors

Combining the new two-dimensional conductive MXene with transition metal oxide to build composite structure is a promising path to improve the conductivity of metal oxide. However, a critical challenge still remains in how to achieve a good combination of MXene and metal oxide. Herein, we develop a facile hydrothermal route to synthesize the MnO₂/Ti₃C₂T_xcomposite electrode for supercapacitors by synergistically coupling MnO₂nanowires with Ti₃C₂T_xMXene nanoflakes. Compared with the pure MnO₂electrode, the morphology of the MnO₂/Ti₃C₂T_xcomposite electrode changes from nanowires to nanoflowers. Moreover, the overall conductivity and electrochemical performance of the composite electrode are greatly improved due to an addition of Ti₃C₂T_xMXene. The specific capacitance of the MnO₂/Ti₃C₂T_xcomposite electrode achieves 210.8 F·g^-1at a scan rate of 2 mV·s^-1, while that of the pure MnO₂electrode is only 55.2 F·g^-1. Furthermore, the specific capacitance of the MnO₂/Ti₃C₂T_xcomposite electrode still can remain at 97.2% even after 10 000 charge-discharge cycles, revealing an excellent cycle stability. The synthesis strategy of this work can pave the way for the research and practical application of the electrode materials for supercapacitors.

Hierarchical V4C3TX@NiO-reduced graphene oxide heterostructure hydrogels and defective reduced graphene oxide hydrogels as free-standing anodes and cathodes for high-performance asymmetric supercapacitors

Asymmetric supercapacitors (ASCs) based on a battery-type anode and a capacitive-type cathode have been attracting extensive interest because of their high energy density. Herein, NiO nanosheets are hydrothermally deposited onto a V₄C₃T_X substrate, which are then assembled into a 3D porous heterostructure hydrogel through a graphene oxide-assisted self-convergence hydrothermal process at low temperatures. The resultant hierarchical V₄C₃T_X@NiO-RGO heterostructure hydrogel exhibits an ultrahigh specific capacitance of up to 1014.5 F g^-1 at 1 A g^-1. In addition, a defective reduced graphene oxide (DRGO) hydrogel is prepared using a cost-effective hydrothermal procedure followed by cobalt-catalyzed gasification, which shows a higher specific capacitance (258 F g^-1 at 1 A g^-1) than the untreated RGO hydrogel (176 F g^-1). These two electrodes are then assembled into an ASC; the device features a stable operating voltage of 1.8 V, a maximum energy density of 86.22 W h kg^-1 at 900 W kg^-1, and excellent cycling stability at 96.4% capacitance retention after 10 000 cycles at 10 A g^-1. The results from this work highlight the unique potential of MXene-based materials for the construction of high-performance ASCs.

Lamellar structured Ni3P2O8: first-ever use to design 1.8 V operated flexible all-solid-state symmetric supercapacitor

Increasing demand for microelectronic devices necessitates the development of highly flexible energy storage technologies with a wide operating voltage. Thus, flexible electrodes and their devices with the requisite mechanical and electrochemical characteristics have prime importance. In this regard, the present article demonstrates the feasibility of designing a flexible all-solid-state supercapacitor using a chemically grown Ni₃P₂O₈ lamellar microstructured electrode embedded with carboxy methyl cellulose-Na₂SO₄ (CMC-Na₂SO₄) gel electrolyte. The formed symmetric device impressively exhibited a maximum working voltage window of 1.8 V with a high specific energy of 44.7 W h kg^-1 and specific power of 3.3 kW kg^-1 along with prolonged cycle life. Also, the device's high deformation tolerance (95%) when bent at 170° with a flashing light-emitting diode (LED) working demonstration showcases its viability for advanced flexible energy storage applications.

High-Energy-Density Asymmetric Supercapacitor Based on Free-Standing Ti3C2TX@NiO-Reduced Graphene Oxide Heterostructured Anode and Defective Reduced Graphene Oxide Hydrogel Cathode

The rational design of an asymmetric supercapacitor (ASC) with an expanded operating voltage window has been recognized as a promising strategy to maximize the energy density of the device. Nevertheless, it remains challenging to have electrode materials that feature good electrical conductivity and high specific capacitance. Herein, a 3D layered Ti₃C₂T_X@NiO-reduced graphene oxide (RGO) heterostructured hydrogel was successfully synthesized by uniform deposition of NiO nanoflowers onto Ti₃C₂T_X nanosheets, and the heterostructure was assembled into a 3D porous hydrogel through a hydrothermal GO-gelation process at low temperatures. The resultant Ti₃C₂T_X@NiO-RGO heterostructured hydrogel exhibited an ultrahigh specific capacitance of 979 F g^-1 at 0.5 A g^-1, in comparison to that of Ti₃C₂T_X@NiO (623 F g^-1) and Ti₃C₂T_X (112 F g^-1). Separately, a defective RGO (DRGO) hydrogel was found to exhibit a drastic increase in specific capacitance, compared to untreated RGO (261 vs 178 F g^-1 at 0.5 A g^-1), owing to abundant mesopores. These two materials were then used as free-standing anode and cathode to construct an ASC, which displayed a large operating voltage (1.8 V), a high energy density (79.02 Wh kg^-1 at 450 W kg^-1 and 45.68 Wh kg^-1 at 9000 W kg^-1), and remarkable cycling stability (retention of 95.6% of the capacitance after 10,000 cycles at 10 A g^-1). This work highlights the unique potential of Ti₃C₂T_X-based heterostructured hydrogels as viable electrode materials for ASCs.