Novel Conductive Metal–Organic Framework for a High-Performance Lithium–Sulfur Battery Host: 2D Cu-Benzenehexathial (BHT)

Despite the high theoretical capacity of lithium–sulfur (Li–S) batteries, their commercialization is severely hindered by low cycle stability and low efficiency, stemming from the dissolution and diffusion of lithium polysulfides (LiPSs) in the electrolyte. In this study, we propose a novel two-dimensional conductive metal–organic framework, namely, Cu-benzenehexathial (BHT), as a promising sulfur host material for high-performance Li–S batteries. The conductivity of Cu-BHT eliminates the insulating nature of most S-based electrodes. The dissolution of LiPSs into the electrolyte is largely prevented by the strong interaction between Cu-BHT and LiPSs. In addition, orientated deposition of Li₂S on Cu-BHT facilitates the kinetics of the LiPS redox reaction. Therefore, the use of Cu-BHT for Li–S battery cathodes is expected to suppress the LiPS shuttle effect and to improve the overall performance, which is ideal for practical application of Li–S batteries

Two-Dimensional Square‑A₂B (A = Cu, Ag, Au, and B = S, Se): Auxetic Semiconductors with High Carrier Mobilities and Unusually Low Lattice Thermal Conductivities

Using evolutionary structure search combined with ab initio theory, we investigate the electronic, thermal, and mechanical properties of two-dimensional (2D) A2B (A = Cu, Ag, Au, and B = S, Se) auxetic semiconductors. Two types of structures are found to have low energy, namely, s­(I/II)-A2B, which have direct bandgaps in the range 1.09–2.60 eV and high electron mobilities. Among these semiconductors, Cu2B and Ag2B have light holes with 2 orders of magnitude larger mobility than the heavy holes, up to 9.51 × 104 cm2 V–1 s–1, giving the possibility of achieving highly anisotropic hole transport with the application of a uniaxial strain. Due to the ionic bonding nature, s-A2B structures have unusually low lattice thermal conductivities down to 1.5 W m–1 K–1 at 300 K, which are quite promising for new generation thermoelectric devices. Besides, s-A2B structures show extraordinary flexibility with ultralow Young’s moduli (down to 20 N/m), which are lower than most previously reported 2D materials. Moreover, under strain along the diagonal direction, five of the structures have in-plane negative Poisson’s ratios

Conductive and Polar Titanium Boride as a Sulfur Host for Advanced Lithium–Sulfur Batteries

Lithium–sulfur batteries are the most promising candidates for advanced electrochemical energy storage systems benefiting from their high energy density and low cost of sulfur. Improving the conductivity of sulfur cathode and stabilizing the polysulfide shuttle are the key factors for obtaining high-performance lithium–sulfur batteries. Herein, metallic and polar TiB2 nanomaterials are applied for the first time as sulfur hosts. The 70S/TiB2 composite exhibits a long-term cycling stability up to 500 cycles at the current density of 1 C. It is worth noting that even when the sulfur areal mass loading is up to 3.9 mg cm–2, a stable capacity of 837 mA h g–1 can be still maintained after 100 cycles. The outstanding electrochemical performance can be attributed to the strong anchoring effect of TiB2 to lithium polysulfides, which is confirmed by the X-ray photoelectron spectroscopy analyses and theoretical calculations with a favorable surface-passivated chemistry. The study presented here will shed a new light for metal borides as hosts to improve the cycling life of lithium–sulfur batteries and provide a deep comprehension of the instinct interaction evolution at a molecular level, which is invaluable in the material rational fabrication for future high-performance Li–S batteries

High Interfacial Thermal Stability of Flexible Flake-Structured Aluminum Thin-Film Electrodes for Bi₂Te₃‑Based Thermoelectric Devices

Environmental thermal energy harvesting based on thermoelectric devices is greatly significant to the advancement of next-generation self-powered wearable electronic devices. However, the rigid electrodes and interface diffusion of electrodes/thermoelectric materials would lead to the wearable discomfort and performance degradation of the thermoelectric device. Here, a flake-structured Al thin-film electrode with high conductivity and excellent reliability is prepared by regulating the microstructure and crystallinity of the films. The as-prepared Al thin film not only maintains its robustness after 1000 bending cycles but also does not delaminate from the substrate when subjected to the 3M tape test, exhibiting excellent flexibility and adhesion to substrate. By comparing with the annealed interface of the double-layer Cu/Bi2Te3 film, the interface of the heat-treated Al/Bi2Te3 film has almost no element diffusion, demonstrating high interfacial thermal stability. Moreover, a thermoelectric temperature sensor based on the Al thin-film electrode is prepared. The sensitivity of the annealed sensor is still linear, and it can stably monitor the temperature variation, showing high reliability. This discovery could provide a facile and effective strategy to achieving highly reliable thermoelectric devices and flexible electronic devices without any additional diffusion barriers

First-Principles Study of the Auxetic and Photocatalytic Properties of Rippled Ge₉C₁₅ Monolayers: Implications for Photocatalytic Water Splitting

Two-dimensional (2D) materials comprising Group-IV elements have garnered significant attention owing to their captivating properties and immense potential for application in nanotechnology. Based on first-principles calculations, we propose a stable configuration of a 2D germanium carbide material, namely, Ge9C15 monolayer, which exhibits a unique rippled geometry. Our calculations reveal that this Ge9C15 monolayer exhibits an anisotropic Young’s modulus ranging from 25.3 to 70.4 GPa·nm, as well as auxeticity characterized by a negative Poisson’s ratio of up to −0.6. The coexistence of sp2 and sp3 hybridization, along with mixed binding characteristics, results in a direct bandgap of 2.06 eV. Remarkably, the electronic properties of the rippled Ge9C15 monolayer, including bandgaps, band edges, and work function, remain robust even under extensile strains of up to 6%. Additionally, it exhibits high sunlight absorption and an appropriate band edge, rendering it highly promising for photocatalytic water splitting. The analysis of Gibbs free energy reveals that the rippled Ge9C15 monolayer possesses photogenerated electrons with a highly favorable redox potential; multiple sites throughout the material fulfill the criteria of hydrogen reduction reaction. These findings expand the application scope of 2D Group-IV materials to diverse fields such as photocatalysis, electronic devices, and nanomechanics

Atomically Thin Bi₂O₂(OH)_1+<i>x</i>(NO₃)_1–<i>x</i> Nanosheets with Regulated Surface Composition for Enhanced Photocatalytic CO₂ Reduction

Solar-driven CO2 with H2O conversion into valuable chemical fuels has attracted considerable attention. However, the low separation efficiency of photogenerated carriers and deficient surface-active sites on catalysts result in low CO2 reduction activity. Herein, the bulk Bi2O2(OH)­(NO3) material was exfoliated to atomically thin nanosheets for shortening the migration distance of photoinduced carriers and enlarging the specific surface area. Photoreduction CO2 test results showed that the CO yield of nanosheets could be enhanced up to nearly six times compared to that of the bulk catalyst. Moreover, a series of ultrathin Bi2O2(OH)1+x(NO3)1–x nanosheets were constructed based on the surface regulation of the OH– concentration on ultrathin nanosheets. The optimized catalyst had an elevated CO yield of 16.7 μmol/g after irradiation for 3 h, about 10 times higher than that of the bulk catalyst. Further theoretical calculations revealed that the superficial NO3– has stronger charge accumulation/depletion behavior with the adjacent Bi atom than surface OH–, conducive to the transfer of photogenerated charge from the bulk phase to the catalyst surface. This work may provide a powerful strategy for the design of a surface-controlled 2D ultrathin photocatalyst for efficient CO2 reduction

Cu-Doping Effect on the Electrocatalytic Properties of Self-Supported Cu-Doped Ni₃S₂ Nanosheets for Hydrogen Production via Efficient Urea Oxidation

The urea oxidation reaction (UOR) is considered as a substitutable oxidation process to supplant the oxygen evolution reaction (OER) for pure and clean hydrogen generation because of its much lower theoretic thermodynamic onset potential. Preparing heteroatomically doped and self-supported three-dimensional (3D) catalysts has become an efficient pathway to promote the electrochemical performance of catalysts. Recently, Cu-based complexes have been investigated as OER catalysts and exhibited improved catalytic activities. However, Cu-doped composites as UOR catalysts have been rarely reported, and the effect of Cu remains unclear in the UOR process. The present work exhibits a self-supported electrocatalyst of Cu-doped Ni3S2 nanosheets supported on Ni foam (NF) synthesized via a direct one-step hydrothermal sulfuration method and unlocks the effect of Cu on the relationship between the catalyst structure and UOR performance. The doping of the Cu element transformed the morphology of Ni3S2 from nanoparticles to nanosheets, increasing the active surface area. Meanwhile, the Cu dopant regulated the electronic structure of Cu-doped Ni3S2 by promoting electron transport from the Ni atom to the Cu dopant, stimulating the formation of active Ni sites with a high valency during UOR. Moreover, the doping of the Cu element optimized the Gibbs adsorption energies of the pivotal intermediates during urea oxidation. Remarkably, as-prepared Cu-doped Ni3S2/NF required only 1.30 V vs RHE toward UOR and an overpotential of 188 mV toward the hydrogen evolution reaction (HER) to deliver 10 mA cm–2 with outstanding electrochemical durability. Besides, the overall urea electrolyzer constructed using Cu-doped Ni3S2/NF as the UOR and HER catalyst needed only 1.57 V to deliver 10 mA cm–2 with stable durability during a long-term test. The present research offers novel insights into the research for designing and preparing efficient and durable electrodes in urea oxidation applications