Although the physicochemical properties of niobium carbide (Nb2C) have been widely investigated, their exploration in the field of photoelectronics is still at the infancy stage with many potential ...applications that remain to be exploited. Hence, it is demonstrated here that few-layer Nb2C MXene can serve as an excellent building block for both photoelectrochemical-type photodetectors (PDs) and mode-lockers. We show that the photoresponse performance can be readily adjusted by external conditions and that Nb2C NSs exhibit a great potential for narrow-band PDs. The demonstrated mechanism was further confirmed by work functions predicted by density functional theory calculations. In addition, as an optical switch for passively mode-locked fiber lasers, ultrastable pulses can be demonstrated in the telecommunication and mid-infrared regions for Nb2C MXene, and as high as the 69th harmonic order with 411 MHz at the center wavelength of 1882 nm can be achieved. These intriguing results indicate that few-layer Nb2C nanosheets can be used as building blocks for various photoelectronic devices, further broadening the application prospects of two-dimensional MXenes.
MXenes, generally referring to two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides, have received tremendous attention since the first report in 2011. Extensive experimental ...and theoretical studies have unveiled their enormous potential for applications in optoelectronics, photonics, catalysis, and many other areas. Because of their intriguing mechanical and electronic properties, together with the richness of elemental composition and chemical decoration, MXenes are poised to provide a new 2D nanoplatform for advanced optoelectronics. This comprehensive review, intended for a broad multidisciplinary readership, highlights the state-of-the-art progress on MXene theory, materials synthesis techniques, morphology modifications, opto-electro-magnetic properties, and their applications. The efforts exploring the device performance limits, steric configurations, physical mechanisms, and novel application boundaries are comprehensively discussed. The review is concluded with a compelling perspective, outlook as well as non-trivial challenges in future investigation of MXene-based nano-optoelectronics.
Since their discovery in 2011, MXenes (abbreviation for transition metal carbides, nitrides, and carbonitrides) have emerged as a rising star in the family of 2D materials owing to their unique ...properties. Although the primary research interest is still focused on pristine MXenes and their composites, much attention has in recent years been paid also to MXenes with diverse compositions. To this end, this work offers a comprehensive overview of the progress on compositional engineering of MXenes in terms of doping and substituting from theoretical predictions to experimental investigations. Synthesis and properties are briefly introduced for pristine MXenes and then reviewed for hetero‐MXenes. Theoretical calculations regarding the doping/substituting at M, X, and T sites in MXenes and the role of vacancies are summarized. After discussing the synthesis of hetero‐MXenes with metal/nonmetal (N, S, P) elements by in situ and ex situ strategies, the focus turns to their emerging applications in various fields such as energy storage, electrocatalysts, and sensors. Finally, challenges and prospects of hetero‐MXenes are addressed. It is anticipated that this review will be beneficial to bridge the gap between predictions and experiments as well as to guide the future design of hetero‐MXenes with high performance.
A comprehensive overview of hetero‐MXenes, from theoretical predictions to experimental investigations, is presented. The reviewed theoretical calculations focus on three sites of MXenes and the reviewed metal‐/nonmetal‐doped/substituted MXenes are experimentally synthesized by in situ/ex situ strategies. It is believed that this work will be beneficial to bridge predictions and experiments, further promoting the development of hetero‐MXenes.
2D PbS nanoplatelets (NPLs) form an emerging class of photoactive materials and have been proposed as robust materials for high‐performance optoelectronic devices. However, the main drawback of PbS ...NPLs is the large lateral size, which inhibits their further investigations and practical applications. In this work, ultra‐small 2D PbS NPLs with uniform lateral size (11.2 ± 1.7 nm) and thickness (3.7 ± 0.9 nm, ≈6 layers) have been successfully fabricated by a facile liquid‐phase exfoliation approach. Their transient optical response and photo‐response behavior are evaluated by femtosecond‐resolved transient absorption and photo‐electrochemical (PEC) measurements. It is shown that the NPLs‐based photodetectors (PDs) exhibit excellent photo‐response performance from UV to the visible range, showing extremely high photo‐responsivity (27.81 mA W−1) and remarkable detectivity (3.96 × 1010 Jones), which are figures of merit outperforming currently reported PEC‐type PDs. The outstanding properties are further analyzed based on the results of first‐principle calculations, including electronic band structure and free energies for the oxygen evolution reaction process. This work highlights promising applications of ultra‐small 2D PbS NPLs with the potential for breakthrough developments also in other fields of optoelectronic devices.
PbS nanoplatelets with uniform lateral size (11.2 ± 1.7 nm) and thickness (3.7 ± 0.9 nm, ≈6 layers) are successfully fabricated by a facile liquid‐phase exfoliation approach. Their potential application in photodetectors (PDs) has been systematically investigated by both experimental measurements and theoretical calculations, achieving figures of merit outperforming currently reported photo‐electrochemical type PDs.
Despite the emerging interest in research and development of Ti3CN MXene nanosheet (NS)-based optoelectronic devices, there is still a lack of in-depth studies of the underlying photophysical ...processes, like carrier relaxation dynamics and nonlinear photon absorption, operating in such devices, hindering their further and precise design. In this paper, we attempt to remedy the situation by fabricating few-layer Ti3CN NSs via combining selective etching and molecular intercalation and by investigating the carrier relaxation possesses and broadband nonlinear optical responses via transient absorption and Z-scan techniques. These results are complemented by first-principle theoretical analyses of the optical properties. Both saturable absorption and reverse saturable absorption phenomena are observed due to multiphoton absorption effects. The analysis of these results adds to the understanding of the basic photophysical processes, which is anticipated to be beneficial for the further design of MXene-based devices.
The electrochemical way of reducing nitrogen to ammonia presents green and economic advantages to dial down irreversible damage caused by the energy-intensive Haber-Bosch process. Here, we introduce ...an advanced catalyst CB7-K
2
B
12
H
12
@Au with highly dispersed and ultrafine nano-gold. The CB7-K
2
B
12
H
12
@Au electrochemically driven ammonia yield and Faraday efficiency is as high as 41.69 μg h
−1
mg
cat.
−1
and 29.53% (at −0.4 V
vs.
RHE), respectively, reaching the US Department of Energy (DOE) utility index of ambient ammonia production along with excellent cycle stability and tolerance that indicates a high potential of industrial practical value. Experimental results and theoretical calculations show that the key to an excellent electrochemical nitrogen reduction performance lies in the smart design of the CB7-K
2
B
12
H
12
@Au catalyst combining the stable substrate anchored Au nanoparticles and K
+
ions that effectively prevent the hydrogen evolution reaction and polarize *N
2
leading to lowering of the rate determining step. This research will promote the further development of electrochemical ammonia production with low environmental impact.
Sustainable ambient electrochemical nitrogen reduction reaction has become a goal pursued by scientists, herein the potassium ion can effectively improve the E-NRR activity of Au anchored on the functional carrier.
The electricity provided by solar or wind power can drive nitrogen in the atmosphere, combining with ubiquitous water to form ammonia, and distributed production methods can alleviate the ...irreversible damage to the environment caused by the energy-intensive Haber–Bosch process. Here, we have designed a novel Ni-doped BCN heterojunction (S/M-BOPs-1) as a catalyst for the electrochemical nitrogen reduction reaction (NRR). The ammonia yield rate and Faraday efficiency in NRR driven by S/M-BOPs-1 reach up to 16.72 μg–1 h–1 cm–2 and 13.06%, respectively. Moreover, S/M-BOPs-1 still maintains high NRR activity and excellent stability after recycling for eight times and long-time operation of 12 h. Using density functional theory calculations, we reveal a possible NRR path for N2 to NH3 on Ni, BCN, and the S/M-BOPs-1 composite surfaces. The interaction between the BCN matrix and Ni nanoparticles promotes a synergetic effect for the electrochemical NRR efficiency due to the partial electron transfer from the Ni particles to BCN that inhibits hydrogen evolution reaction and decreases the rate-determining step on Ni surfaces toward NRR by ∼1.5 times. Therefore, efficient NRR performance can be achieved by tuning the electronic properties of non-noble metals via the formation of a heterointerface.
Abstract
The terms of topological and quantum stabilities of low-dimensional crystalline carbon lattices with multiple non-equivalent sublattices are coined using theoretical analysis, multilevel ...simulations, and available experimental structural data. It is demonstrated that complex low-dimensional lattices are prone to periodicity breakdown caused by structural deformations generated by linear periodic boundary conditions (PBC). To impose PBC mandatory limitations for complex low-dimensional lattices, the topology conservation theorem (TCT) is introduced, formulated and proved. It is shown that the lack of perfect filling of planar 2D crystalline space by structural units may cause the formation of (i) structure waves of either variable or constant wavelength; (ii) nanotubes or rolls; (iii) saddle structures; (iv) aperiodic ensembles of irregular asymmetric atomic clusters. In some cases the lattice can be stabilized by aromatic resonance, correlation effects, or van-der-Waals interactions. The effect of quantum instability and periodicity breakdown of infinite structural waves is studied using quasiparticle approach. It is found that both perfect finite-sized, or stabilized structural waves can exist and can be synthesized. It is shown that for low-dimensional lattices prone to breakdown of translation invariance (TI), complete active space of normal coordinates cannot be reduced to a subspace of TI normal coordinates. As a result, constrained TI subspace structural minimization may artificially return a regular point at the potential energy surface as either a global/local minimum/maximum. It is proved that for such lattices, phonon dispersion cannot be used as solid and final proof of either stability or metastability. It is shown that
ab initio
molecular dynamics (MD) PBC Nosé–Hoover thermostat algorithm constrains the linear dimensions of the periodic slabs in MD box preventing their thermostated equilibration. Based on rigorous TCT analysis, a flowchart algorithm for structural analysis of low-dimensional crystals is proposed and proved to be a powerful tool for theoretical design of advanced complex nanomaterials.
Currently, the development of stable electrochemical nitrogen reduction reaction (ENRR) catalysts with high N2 conversion activity and low cost to instead of the traditional Haber-Bosch ammonia ...production process of high-energy consumption remains a great challenge for researchers. Here, we have immobilized reductive closo-B12H11− boron clusters on a carbon nanotubes (CNT) surface and have successfully prepared a novel Au-CNT catalyst with extraordinary ENRR activity after adding HAuCl4 to the CNT-B12H11− precursor. The excellent properties of ammonia yield (57.7 μg h–1 cm–2) and Faradaic efficiency (11.97%) make it possible to achieve using this Au-CNT catalyst in large-scale industrial production of ammonia. Furthermore, its outstanding cyclic stability and long-term tolerability performance make it one of the most cost-effective catalysts to date. Here, by means of density functional theory we disclose the associative mechanism of N2-to-NH3 conversion on the Au(111) surface, providing visual theoretical support for the experimental results.
Lead selenide (PbSe)‐based nanomaterials have been extensively investigated as building blocks for next‐generation optoelectronic devices owing to their unique properties. In this work, PbSe ...nanocrystals (NCs) have been successfully fabricated by a facile liquid phase exfoliation approach and directly applied as active materials for photo‐electrochemical (PEC)‐type photodetectors (PDs). Taking advantage of broadband absorption and fast carrier dynamics, the PbSe NCs‐based PDs exhibit excellent photo‐current density (11.88 μA cm−2), photo‐responsivity (12.37 mA W−1), response/recovery time (0.12/0.13 s), and long‐term cycling stability. The working mechanism of PbSe NCs‐based PDs is explored by density functional theory calculations based on their structural and electronic properties under various conditions. It is anticipated that this contribution paves the way to readily fabricate low‐dimensional PbSe NCs and extend their practical applications in PEC‐type PDs.
Lead selenide nanocrystals (NCs) are successfully fabricated via facile liquid phase exfoliation and their transient optical responses are investigated by a femtosecond resolved transient absorption spectrometer. The as‐fabricated NCs are applied as active materials for establishing photoelectrochemical type photodetectors. Their photo‐response behaviors are systematically evaluated under various conditions and theoretically illustrated by density functional theory calculations.
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