High-entropy engineering with regulated defect structure and electron interaction tuning active sites for trifunctional electrocatalysis.

High-entropy alloy nanoparticles (HEANs) possessing regulated defect structure and electron interaction exhibit a guideline for constructing multifunctional catalysts. However, the microstructure-activity relationship between active sites of HEANs for multifunctional electrocatalysts is rarely reported. In this work, HEANs distributed on multi-walled carbon nanotubes (HEAN/CNT) are prepared by Joule heating as an example to explain the mechanism of trifunctional electrocatalysis for oxygen reduction, oxygen evolution, and hydrogen evolution reaction. HEAN/CNT excels with unmatched stability, maintaining a 0.8V voltage window for 220 h in zinc-air batteries. Even after 20 h of water electrolysis, its performance remains undiminished, highlighting exceptional endurance and reliability. Moreover, the intrinsic characteristics of the defect structure and electron interaction for HEAN/CNT are investigated in detail. The electrocatalytic mechanism of trifunctional electrocatalysis of HEAN/CNT under different conditions is identified by in situ monitoring and theoretical calculation. Meanwhile, the electron interaction and adaptive regulation of active sites in the trifunctional electrocatalysis of HEANs were further verified by density functional theory. These findings could provide unique ideas for designing inexpensive multifunctional high-entropy electrocatalysts.

Nonmetal Atom Doping Induced Orbital Shifts and Charge Modulation at the Edge of Two-Dimensional Boron Carbonitride Leading to Enhanced Photocatalytic Nitrogen Reduction.

Electronic structure, particularly charge state analysis, plays a crucial role in comprehending catalytic mechanisms. This study focuses on metal-free boron carbonitride (BCN) nanosheets as a case study to investigate the impact of heteroatom doping on the charge state of active sites at the edge of two-dimensional (2D) metal-free nanomaterials. Our observations revealed that the doping induces a shift in the frontier py orbital near the Fermi level, accompanied by alterations in its charge state. These changes provide insights into the nitrogen adsorption descriptors and the critical hydrogenation step, ultimately leading to the proposal of a competitive charge transfer mechanism. Additionally, this exploration has led to the screening of five BCN-type structures (P@T1-C1, S@T1-B1, O@T1-B1, P@T1-B1C2, and P@T1-B1C3) with promising nitrogen reduction reaction (NRR) performances. The BCN structure (S@T1-B1) exhibited the lowest NRR overpotential reaching -0.2 V, which is associated with the proposed charge competition mechanism. Furthermore, the investigation delves into the key step hydrogenation mechanism, descriptors, and volcano diagrams of the conformational relationships. In addition, the proposed doping strategy endows the 2D-BCN with more sensitivity toward the solar spectrum, suggesting its application as a potential photocatalyst. Overall, this study establishes a strong foundation for the advancement of nonmetal-atom-doped BCN nanosheets in nitrogen reduction applications, while also providing a versatile framework for fine-tuning edge-site activity within the broader context of two-dimensional photo/electrocatalytic materials.

Air-Stable Self-Driven UV Photodetectors on Controllable Lead-Free CsCu2I3 Microwire Arrays.

The rapid evolution of the Internet of Things has engendered increased requirements for low-cost, self-powered UV photodetectors. Herein, high-performance self-driven UV photodetectors are fabricated by designing asymmetric metal-semiconductor-metal structures on the high-quality large-area CsCu2I3 microwire arrays. The asymmetrical depletion region doubles the photocurrent and response speed compared to the symmetric structure device, leading to a high responsivity of 233 mA/W to 355 nm radiation. Notably, at 0 V bias, the asymmetric device produces an open-circuit voltage of 356 mV and drives to a short-circuit current of 372 pA; meanwhile, the switch ratio (Iph/Idark) reaches up to 103, indicating its excellent potential for detecting weak light. Furthermore, the device maintains stable responses throughout 10000 UV-light switch cycles, with negligible degradation even after 90-day storage in air. Our work establishes that CsCu2I3 is a good candidate for self-powered UV detection and thoroughly demonstrates its potential as a passive device.

Metal Halide Single Crystals RbCdCl3:Sn2+ and Rb3SnCl7 with Blue and White Emission Obtained via a Hydrothermal Process.

Until now, effective blue light-emitting materials are essentially needed for the creation of white light and precise color renderings in real-world applications, but the efficiency of blue light-emitting materials has lagged far behind. Here, we present a hydrothermal method to synthesize tin-based metal halide single crystals (RbCdCl3:Sn2+ and Rb3SnCl7). Two single crystal materials with different shapes and phases can simultaneously be synthesized in the same stoichiometric ratio. Rb3SnCl7 has a bulk shape, while RbCdCl3:Sn2+ has a needle shape. The deep blue emission (436 nm) of RbCdCl3:Sn2+ can be obtained under the optimal excitation wavelength irradiation. However, pure blue emission (460 nm) to white light can be obtained by changing the excitation wavelength in Rb3SnCl7. The refinement spectra of the electronic structures of RbCdCl3:Sn2+ and Rb3SnCl7 are investigated by density functional theory. It is concluded that the difference in the distribution of Cl energy states leads to the existence of Cl local defect states, which is the reason for the rich luminescence of the two single crystals. These findings provide a path for realizing single-phase broadband white-emitting materials.

Rational Modulation of Single Atom Coordination Microenvironments in a BCN Monolayer for Multifunctional Electrocatalysis.

Single-atom (SA) catalysts (SACs) have demonstrated outstanding catalytic performances toward plenty of relevant electrochemical reactions. Nevertheless, controlling the coordination microenvironment of catalytically active SAs to further enhance their catalytic oerformences has remained elusive up to now. Herein, a systematic investigation of 20 transition metal atoms that are coordinated with 20 different microenvironments in a boroncarbon-nitride monolayer (BCN) is conducted using high-throughput density functional theory calculations. The experimentally synthesized ternary BCN monolayer contains carbon, nitrogen, and boron atoms in its 2D network, thus providing a lot of new coordination environments than those of the current Cx Ny nanoplatforms. By exploring the structural/electrochemical stability, catalytic activity, selectivity, and electronic properties of 400 (20 × 20) TM-BCN moieties, it is discovered that specific SA coordination environments can achieve superior stability and selectivity for different electrocatalytic reactions. Moreover, a universal descriptor to accelerate the experimental process toward the synthesis of BCN-SACs is reported. These findings not only provide useful guidance for the synthesis of efficient multifunctional BCN-SACs but also will immediately benefit researchers by levering up their understanding of the mechanistic effects of SA coordination microenvironments on electrocatalytic reactions.

Highly efficient yellow emission and abnormal thermal quenching in Mn2+-doped Rb4CdCl6.

In this paper, Mn2+-doped Rb4CdCl6 metal halide single crystals were prepared by a hydrothermal method. The Rb4CdCl6:Mn2+ metal halide exhibits yellow emission with photoluminescence quantum yields (PLQY) as high as 88%. Due to the thermally induced electron detrapping, Rb4CdCl6:Mn2+ also displays good anti-thermal quenching (ATQ) behavior with thermal quenching resistance (131% at 220 °C). The increase in the photoionization and the detrapping of the captured electrons from the shallow trap states were appropriately attributed to this exceptional phenomenon based on thermoluminescence (TL) analysis and density functional theory (DFT) calculations. The relationship between the fluorescence intensity ratio (FIR) of the material and temperature change was further explored using the temperature-dependent fluorescence spectrum. It was used as a temperature measuring probe based on absolute sensitivity (Sa) and relative sensitivity (Sb) with the change in temperature. The phosphor-converted white light emitting diodes (pc-WLEDs) were fabricated using a 460 nm blue chip with a yellow phosphor, which has a color rendering index (CRI = 83.5) and a low correlated color temperature (CCT = 3531 K). Because of this, finding new metal halides with ATQ behavior for high-power optoelectronic applications may be made possible by our findings.

Comprehensive Mechanism for CO Electroreduction on Dual-Atom-Catalyst-Anchored N-Doped Graphene.

Carbon neutrality has drawn increasing attention for realizing the carbon cyclization and reducing the greenhouse effect. Although the C1 products, such as CO, can be achieved with a high Faraday efficiency, the targeted production of C2 fuels as well as the mechanism have not been systematically investigated. In this work, we carry out a first-principles study to screen dual-atom catalysts (DACs) for producing C2 fuels through the electrocatalytic carbon monoxide reduction reaction (e-CORR). We find that methanol, ethanol and ethylene can be produced on both DAC-Co and DAC-Cu, while acetate can be achieved on DAC-Cu only. Importantly, methanol and ethylene are preferred on DAC-Co, while acetate and ethylene on DAC-Cu. Furthermore, we show that the explicit solvent can enhance the adsorption and influence the protonation steps, which subsequently affects the protonation and dimerization behavior as well as the performance and selectivity of e-CORR on DACs. We further demonstrate that the C-C coupling is easy to be formed and stabilized if the Integrated Crystal Orbital Hamilton Population (ICOHP) is low because of the low energy barrier. Our findings provide not only guidance on the design of novel catalysts for e-CORR, but an insightful understanding on the reduction mechanism.

Growth of SnX2 (X = Br, I) Single Crystals with Self-Trapped Exciton Emission.

Broadband emission with a large Stokes shift is important to obtain an excellent color rendering index of the solid-state lighting device. Among low-dimensional material and perovskite-like phosphors with broadband self-trapped emission, Sn-based phosphors have attracted much attention due to their high photoluminescence quantum yield (PLQY). However, the disadvantage is that the synthesis of Sn-based phosphors needs to be performed in a glovebox. Upon photoexcitation, the broadband emission of self-trapped excitons results from exciton-phonon coupling induced by the transient distortion of the lattice. Low-dimensional material structures often promote self-trapped emission because of more vibrational degrees of freedom and easier polarization under photoexcitation. Here, zero-dimensional (0D) SnX2 (X = Br, I) single crystals are synthesized by the solvent evaporation method in the air. SnX2 emits blue light, broadband yellow light, and deep red light, among which SnBr2 has the best luminescence performance. The photoluminescence quantum yield (PLQY) of SnBr2 reaches 85% and the Stokes shift reaches 265 nm. The PL intensity of SnX2 is linearly related to excitation power, which preliminarily indicates that the origin of SnX2 luminescence is attributed to self-trapped emission (STE). The white light-emitting diodes (WLEDs) were fabricated using yellow-emitting SnBr2 and blue-emitting BaMgAl10O17:Eu2+, which has a low correlated color temperature (3160 K) and a relatively common color rendering index (79).

Enhanced Optoelectronic Performance Induced by Ion Migration in Lead-Free CsCu2I3 Single-Crystal Microrods.

Lead-free perovskite has attracted great attention in realizing high-performance optoelectronic devices due to their excellent atmospheric stability and nontoxic characteristics. Although a pronounced ion migration effect has been observed in this new class of materials, its potential in enhancing the overall device performance is yet to be fully explored. In this work, we studied the effect of ion migrations on the carrier transport behavior and found that the recoverable migration process can contribute to enhancing the on/off ratio in a lead-free CsCu2I3 single-crystal microrod-based photodetector. In detail, we synthesized CsCu2I3 single-crystal microrods via an in-plane self-assembly supersaturated crystallization approach. These microrods with well-defined morphologies were then used to construct ultraviolet (UV)-band photodetectors, which outperform most reported lead-free perovskite photodetectors based on individual single crystals. Simultaneously, ion migration can result in asymmetric band bending in the two-terminal device, as confirmed by surface potential profiling with Kelvin probe force microscopy (KPFM). Such an effect can be harnessed to increase the on/off ratio by almost an order of magnitude. Furthermore, the lead-free CsCu2I3 single crystal exhibits excellent thermal and air stabilities. These findings demonstrate that the CsCu2I3 single-crystal microrods can be used in stable and efficient photodetection, and the ion migration effect can potentially be utilized for improving the optoelectronic performance of lead-free devices.

Atomically Dispersed Heteronuclear Dual-Atom Catalysts: A New Rising Star in Atomic Catalysis.

Atomic catalysts (AC) are gaining extensive research interest as the most active new frontier in heterogeneous catalysis due to their unique electronic structures and maximum atom-utilization efficiencies. Among all the atom catalysts, atomically dispersed heteronuclear dual-atom catalysts (HDACs), which are featured with asymmetric active sites, have recently opened new pathways in the field of advancing atomic catalysis. In this review, the up-to-date investigations on heteronuclear dual-atom catalysts together with the last advances on their theoretical predictions and experimental constructions are summarized. Furthermore, the current experimental synthetic strategies and accessible characterization techniques for these kinds of atomic catalysts, are also discussed. Finally, the crucial challenges in both theoretical and experimental aspects, as well as the future prospects of HDACs for energy-related applications are provided. It is believed that this review will inspire the rational design and synthesis of the new generation of highly effective HDACs.

Computational Study of the Curvature-Promoted Anchoring of Transition Metals for Water Splitting.

Generating clean and sustainable hydrogen from water splitting processes represent a practical alternative to solve the energy crisis. Ultrathin two-dimensional materials exhibit attractive properties as catalysts for hydrogen production owing to their large surface-to-volume ratios and effective chemisorption sites. However, the catalytically inactive surfaces of the transition metal dichalcogenides (TMD) possess merely small areas of active chemical sites on the edge, thus decreasing their possibilities for practical applications. Here, we propose a new class of out-of-plane deformed TMD (cTMD) monolayer to anchor transition metal atoms for the activation of the inert surface. The calculated adsorption energy of metals (e.g., Pt) on curved MoS2 (cMoS2) can be greatly decreased by 72% via adding external compressions, compared to the basal plane. The enlarged diffusion barrier energy indicates that cMoS2 with an enhanced fixation of metals could be a potential candidate as a single atom catalyst (SAC). We made a well-rounded assessment of the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), which are two key processes in water splitting. The optimized Gibbs free energy of 0.02 for HER and low overpotential of 0.40 V for OER can be achieved when the proper compression and supported metals are selected. Our computational results provide inspiration and guidance towards the experimental design of TMD-based SACs.

Observation and Suppression of Stacking Interface States in Sandwich-Structured Quantum Dot Light-Emitting Diodes.

Interfacial quality of functional layers plays an important role in the carrier transport of sandwich-structured devices. Although the suppression of interface states is crucial to the overall device performance, our understanding on their formation and annihilation mechanism via direct characterization is still quite limited. Here, we present a thorough study on the interface states present in the electron transport layer (ETL) of blue quantum dot (QD) light-emitting diodes (QLEDs). A ZnO/ZnMgO bilayer ETL is adopted to enhance the electron injection into blue QDs. By probing the ETL band structure with photoelectron spectroscopy, we discover that substantial band bending exists at the ZnO/ZnMgO interface, elucidating the presence of a high density of interface states which hinder electron transport. By inserting a ZnO@ZMO interlayer composed of mixed ZnO and ZnMgO nanoparticles, the band bending and thus the interface states are observed to reduce significantly. We attribute this to the hybrid surface properties of ZnO@ZMO, which can annihilate the surface states of both the ZnO and ZnMgO layers. The introduction of a bridging layer has led to ∼40% enhancement in the power efficiency of blue QLEDs and noticeable performance boosts in green and red QLEDs. The findings here demonstrate a direct observation of interface states via detailed band structure studies and outline a potential pathway for eliminating these states for better performances in sandwich-structured devices.

Unravelling the Reaction Mechanisms of N2 Fixation on Molybdenum Nitride: A Full DFT Study from the Pristine Surface to Heteroatom Anchoring.

Transition metal nitrides (TMNs)-based materials have attracted increasing attention in electrochemical nitrogen reduction reaction (eNRR) because of their unique structures and inherent electronic properties. However, the eNRR mechanism on such nitrogen contained catalysts is still unclear, for example, which part of the catalyst act as the active sites, and how to achieve the optimal efficiency is also challenging. In this work, a comprehensive study was conducted to unravel the reaction mechanisms of N2 fixation on molybdenum nitride by using density functional theory (DFT) calculations. The activity and selectivity of eNRR on pristine (001) and (110) Mo5 N6 surfaces as well as few specific numbers of heteroatom-anchored N-terminated surfaces were all evaluated and compared. It was found that the Mo and N atoms on the pristine Mo5 N6 surface were both active for eNRR while following different pathways in mechanism. Moreover, the eNRR catalytic performance of Mo5 N6 could be further boosted by specific metal atoms anchoring, such as single atom, metal dimer, and heterodiatom pair. Finally, a full map of eNRR mechanism on pristine and metal atom-decorated Mo5 N6 surfaces was illustrated. This work not only provides a fundamental understanding of eNRR mechanism on TMNs based materials but also offers powerful strategies towards the rational design of efficient NRR electrocatalysts.

Design of 2D materials - MSi2CxN4-x (M = Cr, Mo, and W; x = 1 and 2) - with tunable electronic and magnetic properties.

Two-dimensional (2D) materials have attracted increasing interest in the past decades due to their unique physical and chemical properties for diverse applications. In this work, we present a first-principles design on a novel 2D family, MSi2CxN4-x (M = Cr, Mo, and W; x = 1 and 2), based on density-functional theory (DFT). We find that all MSi2CxN4-x monolayers are stable by investigating their mechanic, dynamic, and thermodynamic properties. Interestingly, we see that the alignment of magnetic moments can be tuned to achieve non-magnetism (NM), ferromagnetism (FM), anti-ferromagnetism (AFM) or paramagnetism (PM) by arranging the positions of carbon atoms in the 2D systems. Accordingly, their electronic properties can be controlled to obtain semiconductor, half-metal, or metal. The FM states in half-metallic 2D systems are contributed to the hole-mediated double exchange, while the AFM states are induced by super-exchange. Our findings show that the physical properties of 2D systems can be tuned by compositional and structural engineering, especially the layer of C atoms, which may provide guidance on the design and fabrication of novel 2D materials with projected properties for multi-functional applications.