Langmuir–Blodgett Assembly of Ti₃C₂T_x Nanosheets for Planar Microsupercapacitors

Abstract

The rapid development of miniaturized electronic devices has stimulated strong interest in planar microsupercapacitors. Titanium carbide nanosheets (Ti 3 C 2 T x ) have long been considered as an attractive electrode material for such capacitors, given their high pseudocapacitance along with large surface area. State-of-the-art studies with thin films of the nanosheets prepared by methods such as spray-coating have shown specific areal capacitances of a few tens of mF cm −2 and volumetric capacitances of up to 357 F cm −3 . However, most of these results have been obtained from films with thickness over the micrometer range; with the strong interest in portable and transparent devices, it would be favorable to develop ultrathin films with comparable or even improved performance. Herein, the Langmuir−Blodgett (LB) technique is used to produce films of Ti 3 C 2 T x nanosheets with a controllable number of layers, from a single monolayer up to 20 layers. Specific areal capacitances of 1.21 and 5.89 mF cm −2 were obtained from 10 and 20 layer films, respectively, with a retention of ∼90% after 500 cycles. In particular, the thickness of the 20 layer film is ∼140 nm, which gives a volumetric capacitance of nearly 421 F cm −3 . This remarkable performance is attributed to the flat and uniform deposition of the nanosheets in high density for each layer, enabled by the LB technique. This work demonstrates how the LB technique could be utilized for creating high-performance electrodes for planar microsupercapacitors, in particular with film thickness significantly smaller than what can be typically achieved by other methods.

Ultrathin Films of MXene Nanosheets Decorated by Ionic Branched Nanoparticles with Enhanced Energy Storage Stability

“…The enhanced cycling stability of the hybrid electrodes can also be attributed to the aggregation of POSS nanoparticles at the air gaps in between the stacked layers that prevent, to a great extent, further MXene restacking during prolonged cycling . Indeed, MXene-based electrodes reported to date frequently show irreversible capacitance loss, which usually leads to poor cycling stability with capacitance retentions of 46–90% after 500 to 5000 cycles. ,,, The irreversible capacitance loss is typically attributed to restacking of the MXene nanosheets, leading to insufficient electrolyte ion diffusion, as well as to MXene oxidative degradation, deteriorating electronic conductivity . As shown in Figure f and Table S6, in contrast, the improved cycling stability of the POSS-containing supercapacitors studied here is noteworthy in direct comparison with literature results on ultrathin-film (<500 nm electrode thickness) supercapacitors. ,,,− Recent exceptions include reports on thick (>5 μm) shear-delaminated MXene electrodes with good cycling stability up to 500,000 cycles tested in a three-electrode configuration, while other strategies to achieve high capacitance retention include the development of three-dimensional electrodes. , …”

“…The increasing demand for portable, flexible, and wearable electronics has led to an increased need for miniaturized, thin, and lightweight energy storage devices. , Two-dimensional (2D) materials can form flexible and mechanically robust films with high packing density that can meet the requirements of flexible and wearable electronics. Various 2D nanomaterials, such as reduced graphene oxide (rGO), metal oxides, and MXenes, have been considered as active electrode materials using a variety of different fabrication techniques, including layer-by-layer (LbL) methods, spin-coating, spray-coating, and vacuum-assisted filtration. − Among others, rapidly emerging 2D nanomaterials, MXenes, are promising candidates for energy storage applications due to their high electrical conductivity (up to 20,000 S/cm for Ti 3 C 2 T x ), high surface area, and pseudocapacitive behavior, leading to enhanced capacitance values. − Specifically, MXenes represent a family of 2D transition metal carbides, nitrides, and carbonitrides with a general formula of M n +1 X n T x , where M is an early transition metal, X is carbon and/or nitrogen, and T x is the surface terminal group (e.g., −O, −OH, −F, and/or −Cl), with n = 1, 2, 3, or 4 and x representing the number of functional groups per unit . As known, MXenes are typically synthesized using a top-down method by selective etching of A layers from layered ternary nitrides/carbide MAX phases, where A represents an element from group IIIA or IVA of the periodic table …”

Self‐Assembled Monolayer Ti3C2TxMXene as Electron Selective Heterocontact for Crystalline Silicon Solar Cells

“…The thickness of the film is approximately 1.9 nm, which is consistent with the reported thickness characteristics of the monolayer Ti 3 C 2 T x . [ 52 ] The AFM result also showed stacking or folding of the self‐assembled films at a few locations, which is thought to be generated by nonideal splicing and excessive electrostatic forces leading to squeezing between the nanosheets during the self‐assembly process. This should be improved at a later stage by adjusting the solution concentration and surface tension.…”

Self-Competitive Growth of CsPbBr3 Planar Nanowire Array

“…6−8 Great progress has been made in the fabrication of PNAs, which can be categorized into "postgrowth assembly" and "bottom-up growth" routes. The PNA fabrication with "post-growth assembly", such as Langmuir− Blodgett assembly, 9 micromanipulation, 10 and optical tweezers, 11 usually involves multiple steps for collecting, transferring, and rearranging nanowires on substrates, leading to challenges in terms of poor crystal quality, inefficiency, and high cost.…”

“…Semiconductor micro/nanowires have garnered significant attention over the past few decades and are regarded as ideal building blocks for high-performance optical, electroni,c and optoelectronic devices, including waveguides, nanolasers, nanowire transistors, and photodetectors. − Specifically, the planar nanowire arrays (PNAs) play a crucial role in achieving large-scale integration of on-chip devices with advanced functionalities. − Great progress has been made in the fabrication of PNAs, which can be categorized into “postgrowth assembly” and “bottom-up growth” routes. The PNA fabrication with “post-growth assembly”, such as Langmuir–Blodgett assembly, micromanipulation, and optical tweezers, usually involves multiple steps for collecting, transferring, and rearranging nanowires on substrates, leading to challenges in terms of poor crystal quality, inefficiency, and high cost.…”