Surface-Enhanced Raman Spectroscopy and Artificial Neural Networks for Detection of MXene Flakes' Surface Terminations.

The properties of MXene flakes, a new class of two-dimensional materials, are strictly determined by their surface termination. The most common termination groups are oxygen-containing (=O or -OH) and fluorine (-F), and their relative ratio is closely related to flake stability and catalytic activity. The surface termination can vary significantly among MXene flakes depending on the preparation route and is commonly determined after flake preparation by using X-ray photoelectron spectroscopy (XPS). In this paper, as an alternative approach, we propose the combination of surface-enhanced Raman spectroscopy (SERS) and artificial neural networks (ANN) for the precise and reliable determination of MXene flakes' (Ti3C2Tx) surface chemistry. Ti3C2Tx flakes were independently prepared by three scientific groups and subsequently measured using three different Raman spectrometers, employing resonant excitation wavelengths. Manual analysis of the SERS spectra did not enable accurate determination of the flake surface termination. However, the combined SERS-ANN approach allowed us to determine the surface termination with a high accuracy. The reliability of the method was verified by using a series of independently prepared samples. We also paid special attention to how the results of the SERS-ANN method are affected by the flake stability and differences in the conditions of flake preparation and Raman measurements. This way, we have developed a universal technique that is independent of the above-mentioned parameters, providing the results with accuracy similar to XPS, but enhanced in terms of analysis time and simplicity.

Decoding Niobium Carbide MXene Dual-Functional Photoactive Cathode in Photoenhanced Hybrid Zinc-Ion Capacitor.

The coupling of energy harvesting and energy storage discrete modules in a single architecture as a "two-in-one" concept is significant in off-grid energy storage devices. This approach can decrease the device size and the loss of energy transmission in common integrated energy harvesting and storage systems. This work systematically investigates the photoactive characteristics of niobium carbide MXene, Nb2CTx, in a photoenhanced hybrid zinc-ion capacitor (P-ZIC). The unique configuration of the Nb2CTx photoactive cathode absorbs light to charge the capacitor and enables it to operate continuously in the light-powered mode. The Nb2CTx-based P-ZIC shows a photodriven capacitance enhancement of over 60% at the scan rate of 10 mV s-1 under 50 mW cm-2 illumination with 435 nm wavelength. Furthermore, a photoenhanced specific capacitance of ∼27 F g-1, an impressive photocharging voltage response of 1.0 V, and capacitance retention of ∼85% (over 3000 cycles) are obtained.

Tuning Germanane Band Gaps via Cyanoethyl Functionalization for Cutting-Edge Photoactive Cathodes: Photoenhanced Hybrid Zinc-Ion Capacitor Evaluation.

Energy harvesting and storing by dual-functional photoenhanced (photo-E) energy storage devices are being developed to battle the current energy hassles. In this research work, our investigations on the photoinduced efficiency of germanane (Ge-H) and its functionalized analogue cyanoethyl (Ge-C2-CN) are assessed as photocathodes in photo-E hybrid zinc-ion capacitors (ZICs). The evaluated self-powered photodetector devices made by these germanene-based samples revealed effective performances in photogenerated electrons and holes. The photo-E ZICs findings provided a photoinduced capacitance enhancement of ∼52% (for Ge-H) and ∼26% (for Ge-C2-CN) at a scan rate of 10 mV s-1 under 100 mW cm-2 illumination with 435 nm wavelength. Further characterizations demonstrated that the photo-E ZIC with Ge-C2-CN supply higher specific capacitance (∼6000 mF g-1), energy density (∼550 mWh kg-1), and power density (∼31,000 mW kg-1), compared to the Ge-H. In addition, capacitance retention of photo-E ZIC with Ge-C2-CN is ∼91% after 3000 cycles which is almost 6% greater than Ge-H. Interestingly, the photocharging voltage response in photo-E ZIC made by Ge-C2-CN is 1000 mV, while the photocharging voltage response with Ge-H is approximately 970 mV. The observed performances in Ge-H-based photoactive cathodes highlight the pivotal role of such two-dimensional materials to be applied as single architecture in new unconventional energy storage systems. They are particularly noteworthy when compared to the other advanced photo-E supercapacitors and could even be enhanced greatly with other suitable inorganic and organic functional precursors.

Two-Dimensional Van Der Waals Thin Film and Device.

In the rapidly evolving field of thin-film electronics, the emergence of large-area flexible and wearable devices has been a significant milestone. Although organic semiconductor thin films, which can be manufactured through solution processing, have been identified, their utility is often undermined by their poor stability and low carrier mobility under ambient conditions. However, inorganic nanomaterials can be solution-processed and demonstrate outstanding intrinsic properties and structural stability. In particular, a series of two-dimensional (2D) nanosheet/nanoparticle materials have been shown to form stable colloids in their respective solvents. However, the integration of these 2D nanomaterials into continuous large-area thin with precise control of layer thickness and lattice orientation still remains a significant challenge. This review paper undertakes a detailed analysis of van der Waals thin films, derived from 2D materials, in the advancement of thin-film electronics and optoelectronic devices. The superior intrinsic properties and structural stability of inorganic nanomaterials are highlighted, which can be solution-processed and underscor the importance of solution-based processing, establishing it as a cornerstone strategy for scalable electronic and optoelectronic applications. A comprehensive exploration of the challenges and opportunities associated with the utilization of 2D materials for the next generation of thin-film electronics and optoelectronic devices is presented.

Powering the Future: Unleashing the Potential of MXene-Based Dual-Functional Photoactive Cathodes in Photo-Rechargeable Zinc-Ion Capacitor.

Dual-functional photo-rechargeable (photo-R) energy storage devices, which acquire stored energy from solar energy harvesting, are being developed to battle the current energy crisis. In this study, these findings on the photo-driven characteristics of MXene-based photocathodes in photo-R zinc-ion capacitors (ZICs) are presented. Along with the pristine Ti3 C2 Tx MXene, tellurium/Ti3 C2 Tx (Te/Ti3 C2 Tx ) hybrid nanostructure is synthesized via facile chemical vapor transport technique to examine them for photocathodes in ZICs. Interestingly, the evaluated self-powered photodetector devices using MXene-based samples revealed a pyro-phototronic behavior introduced into the samples, with higher desirability observed in Te/Ti3 C2 Tx . The photo-R ZICs results exhibited a capacitance enhancement of 50.86% for Te/Ti3 C2 Tx at two scan rates of 5 and 10 mV s-1 under illumination, compared to dark conditions. In contrast, a capacitance enhancement of 30.20% is obtained for the pristine Ti3 C2 Tx at only a 5 mV s-1 scan rate. Furthermore, both samples achieved photo-charging voltage responses of ≈960 mV, and photoconversion efficiencies of 0.01% (for Te/ Ti3 C2 Tx ) and 0.07% (for Ti3 C2 Tx ). These characteristics in MXene-based single photo-R ZICs are significant and considerable with the distinguished integrated photo-R supercapacitors with solar cells, or coupled energy-harvesting and energy-storing devices reported recently in the literature.

Atomic-layered V2C MXene containing bismuth elements: 2D/0D and 2D/2D nanoarchitectonics for hydrogen evolution and nitrogen reduction reaction.

The exploitation of two-dimensional (2D) vanadium carbide (V2CTx, denoted as V2C) in electrocatalytic hydrogen evolution reaction (HER) and nitrogen reduction reaction (NRR) is still in the stage of theoretical study with limited experimental exploration. Here, we present the experimental studies of V2C MXene-based materials containing two different bismuth compounds to confirm the possibility of using V2C as a potential electrocatalyst for HER and NRR. In this context, for the first time, we employed two different methods to synthesize 2D/0D and 2D/2D nanostructures. The 2D/2D V2C/BVO consisted of BiVO4 (denoted BVO) nanosheets wrapped in layers of V2C which were synthesized by a facile hydrothermal method, whereas the 2D/0D V2C/Bi consisted of spherical particles of Bi (Bi NPs) anchored on V2C MXenes using the solid-state annealing method. The resultant V2C/BVO catalyst was proven to be beneficial for HER in 0.5 M H2SO4 compared to pristine V2C. We demonstrated that the 2D/2D V2C/BVO structure can favor the higher specific surface area, exposure of more accessible catalytic active sites, and promote electron transfer which can be responsible for optimizing the HER activity. Moreover, V2C/BVO has superior stability in an acidic environment. Whilst we observed that the 2D/0D V2C/Bi could be highly efficient for electrocatalytic NRR purposes. Our results show that the ammonia (NH3) production and faradaic efficiency (FE) of V2C/Bi can reach 88.6 µg h-1 cm-2 and 8% at -0.5 V vs. RHE, respectively. Also V2C/Bi exhibited excellent long-term stability. These achievements present a high performance in terms of the highest generated NH3 compared to recent investigations of MXenes-based electrocatalysts. Such excellent NRR of V2C/Bi activity can be attributed to the effective suppression of HER which is the main competitive reaction of the NRR.