Electrochemical capacitors (ECs) that store charge based on the pseudocapacitive mechanism combine high energy densities with high power densities and rate capabilities. 2D transition metal carbides (MXenes) have been recently introduced as high‐rate pseudocapacitive materials with ultrahigh areal and volumetric capacitances. So far, 20 different MXene compositions have been synthesized and many more are theoretically predicted. However, since most MXenes are chemically unstable in their 2D forms, to date only one MXene composition, Ti3C2T
MXenes constitute a rapidly growing family of 2D materials that are promising for optoelectronic applications because of numerous attractive properties, including high electrical conductivity. However, the most widely used titanium carbide (Ti3C2T
- Award ID(s):
- 2041050
- NSF-PAR ID:
- 10371490
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 34
- Issue:
- 41
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract x , has shown stable pseudocapacitive charge storage. Here, a cation‐driven assembly process is demonstrated to fabricate highly stable and flexible multilayered films of V2CTx and Ti2CTx MXenes from their chemically unstable delaminated single‐layer flakes. The electrochemical performance of electrodes fabricated using assembled V2CTx flakes surpasses Ti3C2Tx in various aqueous electrolytes. These electrodes show specific capacitances as high as 1315 F cm−3and retain ≈77% of their initial capacitance after one million charge/discharge cycles, an unprecedented performance for pseudocapacitive materials. This work opens a new venue for future development of high‐performance supercapacitor electrodes using a variety of 2D materials as building blocks. -
Transition metal carbides (MXenes) are an emerging family of highly conductive two-dimensional materials with additional functional properties introduced by surface terminations. Further modification of the surface terminations makes MXenes even more appealing for practical applications. Herein, we report a facile and environmentally benign synthesis of reduced Ti 3 C 2 T x MXene (r-Ti 3 C 2 T x ) via a simple treatment with l -ascorbic acid at room temperature. r-Ti 3 C 2 T x shows a six-fold increase in electrical conductivity, from 471 ± 49 for regular Ti 3 C 2 T x to 2819 ± 306 S m −1 for the reduced version. Additionally, we show an enhanced oxidation stability of r-Ti 3 C 2 T x as compared to regular Ti 3 C 2 T x . An examination of the surface-enhanced Raman scattering (SERS) activity reveals that the SERS enhancement factor of r-Ti 3 C 2 T x is an order of magnitude higher than that of regular Ti 3 C 2 T x . The improved SERS activity of r-Ti 3 C 2 T x is attributed to the charge transfer interaction between the MXene surface and probe molecules, re-enforced by an increased electronic density of states (DOS) at the Fermi level of r-Ti 3 C 2 T x . The findings of this study suggest that reduced MXene could be a superior choice over regular MXene, especially for the applications that employ high electronic conductivity, such as electrode materials for batteries and supercapacitors, photodetectors, and SERS-based sensors.more » « less
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Abstract In this work, Ti3C2T
x MXene was investigated as a nanofluidic anolyte additive in vanadium redox flow batteries to improve the sluggish kinetics of V2+/V3+redox reaction. Numerous electrochemical tests under flow and static conditions were performed to demonstrate the effectiveness of MXenes for VRFB applications. Pressure drop tests and morphology analysis were also conducted to better understand the hydraulic effects of MXene addition into the anolyte. The nanofluidic anolytes with the concentration of 0.10 and 0.15 wt% showed the best electrochemical performance, although the former induced less aggravated hydraulic effects within a reasonable pressure drop range. At a current density of 200 mA cm−2, the nanofluidic analyte containing 0.10 wt% MXene was able to utilize 67 % of the theoretical capacity. Contrarily, with the pristine anolyte, only 10 % of the theoretical capacity could be utilized due to excessive losses. Moreover, the energy efficiency up to 74 % is observed for the nanofluidic electrolyte, which is an increase of 25 % compared to the pristine anolyte. Primarily, the enhanced battery performance was attributed to the improved electrocatalytic activity towards the anodic V2+/V3+redox reaction. Furthermore, a dynamic, web‐like, flowing electrode network is shown to increase the mass transport capacity of porous carbon felt electrodes by creating additional, abundant, and electrochemically active surfaces within the pores. -
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Abstract Next‐generation electronics and energy technologies can now be developed as a result of the design, discovery, and development of novel, environmental friendly lead (Pb)‐free ferroelectric materials with improved characteristics and performance. However, there have only been a few reports of such complex materials’ design with multi‐phase interfacial chemistry, which can facilitate enhanced properties and performance. In this context, herein, novel lead‐free piezoelectric materials (1‐
x )Ba0.95Ca0.05Ti0.95Zr0.05O3‐(x )Ba0.95Ca0.05Ti0.95Sn0.05O3, are reported, which are represented as (1‐x )BCZT‐(x )BCST, with demonstrated excellent properties and energy harvesting performance. The (1‐x )BCZT‐(x )BCST materials are synthesized by high‐temperature solid‐state ceramic reaction method by varyingx in the full range (x = 0.00–1.00). In‐depth exploration research is performed on the structural, dielectric, ferroelectric, and electro‐mechanical properties of (1‐x )BCZT‐(x )BCST ceramics. The formation of perovskite structure for all ceramics without the presence of any impurity phases is confirmed by X‐ray diffraction (XRD) analyses, which also reveals that the Ca2+, Zr4+, and Sn4+are well dispersed within the BaTiO3lattice. For all (1‐x )BCZT‐(x )BCST ceramics, thorough investigation of phase formation and phase‐stability using XRD, Rietveld refinement, Raman spectroscopy, high‐resolution transmission electron microscopy (HRTEM), and temperature‐dependent dielectric measurements provide conclusive evidence for the coexistence of orthorhombic + tetragonal (Amm2 +P4mm ) phases at room temperature. The steady transition ofAmm2 crystal symmetry toP4mm crystal symmetry with increasingx content is also demonstrated by Rietveld refinement data and related analyses. The phase transition temperatures, rhombohedral‐orthorhombic (TR‐O), orthorhombic‐ tetragonal (TO‐T), and tetragonal‐cubic (TC), gradually shift toward lower temperature with increasingx content. For (1‐x )BCZT‐(x )BCST ceramics, significantly improved dielectric and ferroelectric properties are observed, including relatively high dielectric constantε r≈ 1900–3300 (near room temperature),ε r≈ 8800–12 900 (near Curie temperature), dielectric loss, tanδ ≈ 0.01–0.02, remanent polarizationP r≈ 9.4–14 µC cm−2, coercive electric fieldE c≈ 2.5–3.6 kV cm−1. Further, high electric field‐induced strainS ≈ 0.12–0.175%, piezoelectric charge coefficientd 33≈ 296–360 pC N−1, converse piezoelectric coefficient ≈ 240–340 pm V−1, planar electromechanical coupling coefficientk p≈ 0.34–0.45, and electrostrictive coefficient (Q 33)avg≈ 0.026–0.038 m4C−2are attained. Output performance with respect to mechanical energy demonstrates that the (0.6)BCZT‐(0.4)BCST composition (x = 0.4) displays better efficiency for generating electrical energy and, thus, the synthesized lead‐free piezoelectric (1‐x )BCZT‐(x )BCST samples are suitable for energy harvesting applications. The results and analyses point to the outcome that the (1‐x )BCZT‐(x )BCST ceramics as a potentially strong contender within the family of Pb‐free piezoelectric materials for future electronics and energy harvesting device technologies. -
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Abstract Textile devices have benefited from the discovery of new conductive materials and innovations in textile device design. These devices include textile‐based supercapacitors (TSCs), encompassing fiber, yarn, and fabric supercapacitors, which have demonstrated practical value in powering wearable devices. Recent review articles have highlighted the limited energy density of TSCs as an important challenge, demanding new electrode materials with higher electronic conductivity and theoretical capacitance than present materials. Ti3C2T
x , a member of the MXene family, is known for its metallic conductivity and high volumetric capacitance in acidic electrolytes due to its pseudocapacitive behavior. Driven by these excellent properties, recent literature has reported promising integration methods of Ti3C2Tx into TSCs with significantly improved areal and volumetric capacitance compared with non‐MXene‐based TSCs. Furthermore, knitted MXene‐based TSCs demonstrated practical application of wearable energy storage devices in textiles. Herein, the techniques used to produce MXene‐based fibers, yarns, and fabrics and the progress in architecture design and performance metrics are highlighted. Challenges regarding the introduction of this new material into fiber/yarn/fabric architectures are discussed, which will inform the development of textile‐based devices beyond energy storage applications. Opportunities surrounding the development of MXene‐based fibers with tunable mechanical, electrical, and electrochemical properties are proposed, which will be the direction of future research efforts.
