Formation Energy Research Articles

Investigation of optical and thermoelectric characteristics of novel zintl-phase alloys CaZn2X2 (X = P, As, Sb) for green energy applications

Abstract This study examines the photovoltaic and thermoelectric response of calcium-based novel Zintl-phase alloys CaZn2X2 (X = P, As, Sb). The structural, optoelectronics, and transport features of Zintl CaZn2X2 (X = P, As, Sb) compounds have been analyzed using the full potential linearized augmented plane wave (FPLAPW) technique. Investigations on formation energy and phonon dispersion have confirmed the formation and dynamical stabilities. These compounds exhibit a semiconductor behavior, as their predicted bandgap values: 1.76 eV for CaZn2P2, 1.14 eV for CaZn2As2, and 0.32 eV for CaZn2Sb2. By investigating the optical properties, we have discovered their potential applicability in optoelectronic and photovoltaic devices, as evidenced by the optical response of these phases. The traditional Boltzmann transport theory has assessed transport characteristics against temperature and chemical potential. Significantly higher values of the Seebeck coefficient are achieved at room and elevated temperatures. Moreover, the power factor demonstrates a linear relationship with rising temperature. The remarkable optoelectronic properties and exceptional power factor values suggest that these materials are suitable for deployment in photovoltaic and transport devices.

Mechanical, electronic, optical, and thermoelectric properties of Rb2TlGaX6 (X = F, I) lead free double perovskites: A first-principles study

Abstract Halide perovskites play an important role in the renewable energy industry and are the top substitutes for Pb-halide perovskites. This study investigates the structural, mechanical, electronic, optical, and thermoelectric properties of the double halide perovskites Rb2TlGaX6 (X = F, I) using density functional theory (DFT) at WIEN2k interfaces. The structural, mechanical, and thermal stabilities are evaluated using the tolerance factor, Born-Huang criteria, and negative formation energy. The obtained lattice constants are 9.31 Å and 24.93 Å, for Rb2TlGaF6 and Rb2TlGaI6 respectively. Rb2TlGaF6 is brittle and Rb2TlGaI6 is ductile. Both compounds exhibit anisotropic behavior. The indirect semiconducting nature (L-X) is demonstrated by the estimated bandgap values of 6.05 eV (4.31 eV) and 1.06 eV (0.52 eV), for Rb2TlGaF6 and Rb2TlGaI6 respectively, using the TB-mBJ (PBE-GGA) potential. Distinctive optical characteristics are studied, including the dielectric function, loss function, conductivity, reflectivity, refractive index, and absorption coefficient. Based on the investigation, both materials exhibit excellent optical conductivity, high light absorption throughout the UV–visible spectrum, and low reflection (within 20% for Rb2TlGaF6 and 40% for Rb2TlGaI6). Lastly, various thermoelectric properties are explored by varying the temperature. Both compounds show a high Seebeck coefficient and low thermal conductivity. The maximum figure of merit (ZT) obtains of 0.61 and 0.81, for Rb2TlGaF6 and Rb2TlGaI6, respectively. These results demonstrate the suitability of Rb2TlGaF6 and Rb2TlGaI6 for thermoelectric and photovoltaic applications.

Nucleation‐Controlled Doping of II–VI Semiconductor Nanocrystals Mediated by Magic‐Sized Clusters

Doping quantum‐confined semiconductor nanocrystals offers an effective way to tailor their unique properties. However, the inherent challenges of nanoscale doping processes, such as the low probability of successful doping, have hindered their practical applications. Nucleation‐controlled doping has emerged as a potential solution, but a comprehensive mechanistic understanding of this process is lacking. Herein, the nucleation‐controlled doping process facilitated by magic‐sized cluster intermediates is elucidated. This approach enables the synthesis of 2D ZnSe quantum nanoribbons with two distinct doping sites. Remarkably, the identity of the dopants plays a critical role in determining the chemical pathways of nucleation‐controlled doping. Substitutional doping of magic‐sized clusters with Mn2+ ions leads to successful substitutional doping of the final 2D nanocrystals. Conversely, Co2+ ions, initially occupying substitutional positions in the magic‐sized cluster intermediates, relocate to alternative sites, such as interstitial sites, in the final nanocrystals. First‐principle calculations of dopant formation energies support these experimental findings, demonstrating the thermodynamic favorability of specific dopant site preferences. Moreover, a consistent tendency is observed in CdSe nanocrystals, suggesting that the proposed doping mechanism is generally applicable to II–VI semiconductors. This study will advance the controlled synthesis of various doped semiconductor nanocrystals using nucleation‐controlled doping processes.

Flame Speed Measurements of Ammonia–Hydrogen Mixtures for Gas-Turbines

Abstract Recent findings from the U.S. Energy Information Administration project an increase in domestic fossil fuel consumption (e.g., petroleum and natural gas) and global greenhouse gas emissions through 2050 (Nalley, S., 2021, “International Energy Outlook 2021 (IEO2021),” IEO2021 Release, CSIS, Center for Strategic and International Studies, Washington, DC, Technical Presentation, pp. 2–12). Consequently, advanced combustion research aims to identify fuels to mitigate fossil fuel consumption while minimizing exhaust emissions. Ammonia (NH3) is one of these candidates, as it has historically been shown to provide high energy potential and zero-carbon emission (CO and CO2) (Hayakawa, A., Goto, T., Mimoto, R., Arakawa, Y., Kudo, T., and Kobayashi, H., 2015, “Laminar Burning Velocity and Markstein Length of Ammonia/Air Premixed Flames at Various Pressures,” Fuel, 159, pp. 98–106). As a hydrogen (H2) carrier, NH3 serves as a possible solution to the U.S. Department of Energy's Hydrogen Program Plan by providing efficient H2 storage and conservation capabilities (U.S. Department of Energy, 2020, “Department of Energy Hydrogen Program Plan,” U.S. Department of Energy, Washington, DC, Report No. DOE/EE-2128). As a result, applied turbine-combustion research of NH3 and H2 fuel has been conducted to identify combustion performance parameters that aid in the design of sustainable turbomachinery (Chiong, M.-C., Chong, C., Ng, J., Mashruk, S., Chong, W., Samiran, N., Mong, G., and Medina, A., 2021, “Advancements of Combustion Technologies in the Ammonia-Fuelled Engines,” Energy Convers. Manage., 244, p. 114460). One of these key combustion parameters is the laminar burning speed (LBS). While abundant literature exists on the combustion of NH3 and H2 fuels, there is not sufficient evidence in high-pressure environments to provide a comprehensive understanding of NH3 and H2 combustion phenomena in turbine-combustor settings. To advance the state of the knowledge, NH3 and H2 mixtures were ignited in a spherical chamber across a range of equivalence ratios at 296 K and 5 atm to understand their flame characteristics and LBS which was determined using a multizone constant volume method. The experimental conditions were selected according to primary turbine-combustor conditions, as much research is needed to support NH3–H2 applicability in turbomachinery for power generation. The effect of H2 addition to NH3 fuel was observed by comparing the LBS for various NH3–H2 mixture compositions. Experimental results revealed increased LBS values for H2 enriched NH3, with the maximum LBS occurring at stoichiometry. The experimental data were accurately predicted by the University of Central Florida (UCF) NH3–H2 mechanism developed for this investigation, while NUI 1.1 simulations overestimated recorded LBS data by a significant margin. This study demonstrates and quantifies the enhancing effect of H2 addition to NH3 fuels via LBS and strengthens the literature surrounding NH3–H2 combustion reactions for future work.

Theoretical Study on Pt1/CeO2 Single Atom Catalysts for CO Oxidation

Understanding the influence of structural configurations on catalytic performance is crucial for optimizing atom‐efficient single‐atom catalysts (SACs). In this study, we conducted a density functional theory (DFT) investigation of single Pt atoms positioned at step‐edges and within a solid solution on the CeO2(111) surface. We compared these configurations in terms of thermodynamic stability, electronic properties, and further potential energy surfaces for CO oxidation. Stability studies revealed that the solid solution catalyst exhibits greater stability compared to the step‐edge catalyst. Additionally, the Pt in the solid solution catalyst can effectively activate lattice oxygen atoms, making the catalyst more conducive to the formation of oxygen vacancies. The CO oxidation process was analyzed using the Mars‐van Krevelen mechanism, revealing that the solid solution catalyst possesses a more moderate CO adsorption energy. This, coupled with its lower oxygen vacancy formation energy, leads to reduced energy barriers throughout the CO oxidation cycle. Our findings highlight the strong dependence of catalytic activity on the specific configuration of Pt atoms within the CeO2 matrix, with the solid solution model demonstrating superior catalytic efficiency compared to the step‐edge‐supported Pt catalysts.

Au-Doped Black Silicon Photodetector Fabricated by a Femtosecond Laser with Excellent Near-Infrared Response.

Silicon photonic devices are key components in optical imaging and sensing for communication, and the development of silicon-based photodetectors with ideal performance in the visible and infrared spectral ranges can promote the application of silicon photonics in various photoelectronic systems. Here, a Au-doped black silicon photodetector was prepared by a femtosecond laser direct writing technique. The conical micro-/nanostructures with different sizes were produced by different laser fluence irradiation. Ultrafast pump-probe technology revealed that the strong spallation process and phase explosion between Au and silicon facilitate the interfusion of Au atoms into the silicon lattice. EDS analyses, Raman spectra, and XPS spectra show the uniform distribution of Au elements, multiconfiguration amorphous phase transition, and stable chemical valence states of Au elements in Au-doped black silicon layers, respectively. The excellent geometric light trapping performance of the surface conic structure-assisted photodetector achieved a high absorptance of 95% in the 200-1100 nm band. Simultaneously, the introduction of the intermediate band by Au hyperdoping also leads to a strong absorptance of 75% in the 1100-2500 nm band. The photoelectrical response rate of the Au-doped black silicon photodetectors increased by 10 times in the infrared wavelength band by means of the introduced intermediate energy levels through Au element doping. The switching photocurrent ratio is also found to be boosted 10 times, which comes from the reduction of the photon injection barrier. The excellent photoelectronic properties lead to the increased potential of femtosecond laser processing for integration with photonics and electronics, which shows great possibilities in the further progress of energy devices, information technology, and artificial intelligence.

High-precision prediction of microalgae biofuel production efficiency: employing ELG ensemble method

Microalgae biofuels are considered a significant source of future renewable energy due to their efficient photosynthesis and rapid growth rates. However, practical applications face numerous challenges such as variations in environmental conditions, high cultivation costs, and energy losses during production. In this study, we propose an ensemble model called ELG, integrating Empirical Mode Decomposition (EMD), Long Short-Term Memory (LSTM), and Gradient Boosting Machine (GBM), to enhance prediction accuracy. The model is tested on two primary datasets: the EIA (U.S. Energy Information Administration) dataset and the NREL (National Renewable Energy Laboratory) dataset, both of which provide extensive data on biofuel production and environmental conditions. Experimental results demonstrate the superior performance of the ELG model, achieving an RMSE of 0.089 and MAPE of 2.02% on the EIA dataset, and an RMSE of 0.1 and MAPE of 2.21% on the NREL dataset. These metrics indicate that the ELG model outperforms existing models in predicting the efficiency of microalgae biofuel production. The integration of EMD for preprocessing, LSTM for capturing temporal dependencies, and GBM for optimizing prediction outputs significantly improves the model’s predictive accuracy and robustness. This research, through high-precision prediction of microalgae biofuel production efficiency, optimizes resource allocation and enhances economic feasibility. It advances technological capabilities and scientific understanding in the field of microalgae biofuels and provides a robust framework for other renewable energy applications.

Demystifying Synergistic Multifunctional Electrocatalysis of N-Doped Graphene/WS2 Heterostructure with Single-Atom Catalysts for Water Splitting and Fuel Cells.

As the demand for sustainable energy continues to rise, electrocatalysis has become increasingly prominent in the advancement of clean energy technologies. By scrutinizing the material to function as a multifunctional catalyst, the effectiveness of energy conversion processes is significantly enhanced. This study focuses on harnessing graphene/WS2 van der Waals heterostructures for overall water splitting and fuel cell applications, using transition metals (TMs) from Sc-Zn as single-atom catalysts (SACs). Additionally, the research explores the synergistic effect of nitrogen doping combined with SACs to modify the material into multifunctional catalysts. The stability of all TMs as SACs in the vdW heterostructure (TM@GW) and nitrogen-doped TM@GW (TM@NGW) is validated with negative cohesive and formation energies, and thermodynamic stability is also corroborated with ab initio molecular dynamics (AIMD) analysis at both 300 and 500 K for 5 ps. The observed electrocatalytic performance of TM@GW and TM@NGW depicts that the Ni@NGW system exhibits trifunctional property with the lowest overpotentials {ηHER; ηOER; ηORR = 0.21; 0.42; 0.27 V}. Additionally, the Cr@NGW material displays bifunctional catalytic activity for the OER and ORR, with overpotentials of 0.53 and 0.37 V, respectively. The synergistic effect between N doping and SACs is further studied with the d, p band centers and density of states calculations. Furthermore, the scaling relation between the adsorption of intermediates and reaction kinetics is studied, which validates the coaction of N and SACs in the TM@NGW heterostructure. This study demonstrates that the inclusion of SACs and nitrogen atoms in the GW heterostructure significantly enhances the catalytic performance by approximately 26%, effectively transforming the system into a multifunctional catalyst. These findings emphasize the role of SACs in vdW heterostructures and N doping effects, providing valuable insights to guide the design of advanced catalysts for water splitting and fuel cell applications.

Thermodynamic modeling of the structure of alkali aluminophosphate glasses and their ionic conductivity

AbstractThis study presents the structural and ionic conductivity thermodynamic modeling for glasses with compositions in the system 50M2O‐xAl2O3‐(50 − x)P2O5, with M = Li or K. The Shakhmatkin and Vedishcheva thermodynamic model (SVTDM), or associated solutions model, has been previously used in successfully predicting the structure of simple binary phosphate glasses and it has now been employed with the aim to discerning the model's capability to predict the structural changes induced in the phosphate network by the addition of alumina. The results have been furthermore validated through their comparison with literature experimental data on the structural characterization of the glasses by 31P NMR measurements as well as on ionic conductivity determined by impedance spectroscopy. Although this methodology demonstrates good agreement with experimental data on the structure of aluminophosphate glasses, some disparities persist, potentially arising from experimental uncertainties. However, SVTDM faces limitations, including the need for comprehensive knowledge of stable phases and their formation energies. Predictions of ionic conductivity, though promising, exhibit deviations from experimental values, attributed to factors such as the influence of the chemical environment on dielectric properties. To enhance accuracy in conductivity prediction, a deeper understanding of additional variables such as dielectric constant and attempt frequency is imperative.

Half‐Heusler Alloy CoMnZ (Z = Sb/Sn): Electrode Material for Lithium‐Ion Batteries

ABSTRACTHeusler alloys (HAs) are a well‐known family of compounds generating promising interest due to their robust structure, ease of tailoring their unique properties, and potential applications. The investigations in the direction of the electrochemical performance of these materials as electrodes for rechargeable lithium‐ion batteries (LIBs) have been established theoretically and experimentally. Alloying of alkali metal ions into half‐HAs unit cells can be another route to improve LIBs performance. This work presents our investigations on thermodynamically stable half‐HAs CoMnZ (Z: Sb/Sn) as electrode materials for rechargeable LIBs using the first‐principle calculations based on the density functional theory. The negative formation energies validate the thermodynamic stability of the alloys considered in this study. With increasing Li doping, a structural change from cubic to tetragonal and orthorhombic phase is observed in the host structure, and upon full lithiation (LiMnZ), a cubic structure is attained. The band structure calculations of the host structure and its lithiated phase indicate a metallic nature in these alloys. The calculations are also performed to investigate the structural stability of parent alloys and corresponding lithiated phases. We calculated a storage capacity of around 14.5 Ah/kg for 0.125 atomic fraction of Li atoms, which is increased by nearly 10 times upon full lithiation. A maximum open circuit voltage of around 9.8 V is calculated for Li0.125Co0.875MnSb and CoLi0.125Mn0.875Sb. Thus, all these remarkable results suggest that these intermetallic compounds have a strong potential as the cathode material for LIBs with a robust life and a large capacity.

Forecasting Electric Vehicle Adoption in the USA Using Machine Learning Models

Electric vehicles (Electric Vehicles) are at the vanguard of the global dispensation to sustainable transportation, depicting a pivotal step toward diminishing greenhouse gas emissions and reliance on fossil fuels. Notwithstanding, the adoption of Electric Vehicles has been growing in the USA, but their future remains at a crossroads. The objective of the research is to design and execute machine learning models capable of providing accurate predictions of future trends in electric vehicle adoption in the USA. The dataset gathered for analyzing EV adoption in the USA comprises data across three primary categories: environmental data, economic indicators, and policy-related data. The economic indicators include household income, fuel prices, electricity rates, and lithium battery costs that affect EV purchasing power obtained from the U.S. Census Bureau and the U.S. Energy Information Administration (EIA). Environmental data include greenhouse gas emissions and air quality indices from the EPA, providing information on regional environmental conditions that might affect EV attractiveness. Other policy data included federal and state incentives such as tax credits, rebates, and EV infrastructure data, collected from the U.S. Led by the U.S. Department of Energy's Alternative Fuels Data Center and the Energy Laboratory, additional EV sales trends were pulled from databases of the automotive industry. In this research project, credible and proven machine learning models were employed, most notably, Linear Regression, Random Forest, and XG-Boost. The performance of the models was tested for EV adoption prediction by considering a few important metrics: Mean Absolute Error (MAE), Root Mean Squared Error (RMSE), and R-squared (R²). From the model performance metrics presented, the Gradient Boosting Regressor and Random Forest models performed far better by a big margin than Linear Regression. The prediction models, particularly, the Random Forest regressors and Gradient Boosting regressors demonstrated incredible forecasting of electric vehicle adoption. The model works excellently on the premise that historical data with relevant features can be utilized to gain some valuable insight into future trends. Policy-makers interested in stimulating the wider use of electric vehicles can ensure that targeted policies address both current barriers and future demands. Results of this analysis suggest incentives, such as tax credits, rebates, and subsidies, are some of the most common actions to reduce the upfront cost of an EV, a key circumventing factor in the choice that many consumers face.

Investigation of the Optoelectronic, γ‐Attenuation, and Thermodynamic Properties of Novel MnGa2P3H4NO14 for Energy Applications: A DFT Study

ABSTRACTTransparent conducting oxides (TCOs) from the semiconductor family have garnered considerable interest due to the growing popularity of optoelectronic and thermodynamical applications. Our present study has presented findings on the electronic, optical, and thermodynamic characteristics of spinel oxide MnGa2P3H4NO14; using density functional theory (DFT), we utilized first‐principles calculations carried out with the Wien 2 k software package. The calculations were performed using the generalized‐gradient‐approximation plus Hubbard potential U (GGA+U) method for the doped materials. The band structure calculation reveals that the parent compound exhibits a semiconducting nature and a direct band gap of 2.9 and 1.7 eV for spin‐up and down channels, respectively. The stability of the material is assessed by evaluating its formation energies, which reveal that spinel oxide exhibits the highest stability. The thermodynamic properties are determined using the quasiharmonic Debye model, implemented in the GIBBS 2 code. Furthermore, the quasiharmonic Debye model examines the pressure and temperature dependence of all parameters related to the investigated spinel oxides. In order to evaluate the effectiveness of the radiation shielding, we computed the mass attenuation coefficient for the XCOM program that was investigated from the sample. In addition, linear attenuation, half‐value layer, and mean free path values have been evaluated. A thorough investigation into the dielectric function's optical characteristics was conducted. It has been found that the dielectric function exhibits a wide range of energy transparency. The discovery of UV‐absorbing materials with extremely narrow band gaps suggests their potential use in optoelectronic and solar cell applications. These results provide solid proof and motivation for seeking cutting‐edge optoelectronic materials and technology.

A new analytical technique for obtaining the optimal sizing, location, and scheduling of BESS in a grid-connected microgrid with multiple cases of heavy DG penetration

This paper aims to provide an optimal location, power, and energy rating for a battery energy storage system (BESS) in a grid-connected microgrid. The microgrid is pre-installed with heavy renewable distributed generations like solar and wind power plants. The paper suggests a straightforward optimal operating schedule for BESS, considering real-time data on solar irradiance, wind speed, load profile, and electricity tariff obtained from the US Energy Information Administration. The proposed method analytically identifies the optimal size and location of the storage system using the modified Q-PQV load flow technique. The method also proposes incorporating seasonal variations of the real-time data to obtain the optimal BESS size. A detailed cost-benefit analysis is exhibited to validate the economic feasibility. The methodological superiority is established by comparing the proposed algorithm with other soft computing techniques like PSO, GA, and JAYA algorithms. The novel technique is executed on 33-bus and 136-bus test systems with multiple cases of solar and wind-distributed generations. The proposed method provided a significant reduction in annual energy loss with a definite improvement in the voltage profile and overall profit of the system.

Constructing an Active Sulfur-Vacancy-Rich Surface for Selective *CH3-CH3 Coupling in CO2-to-C2H6 Conversion With 92% Selectivity.

To achieve high selectivity in photocatalytic CO2 reduction to C2+ products, increasing the number of CO2 adsorption sites and lowering the energy barriers for key intermediates are critical. A ZnIn2S4 (ZIS)/MoO3-x (Z-M) photocatalyst is presented, in which plasmonic MoO3-x generates hot electrons, creating a multielectron environment in ZIS that facilitates efficient C─C coupling reactions. Density functional theory (DFT) calculations reveal that MoO3-x reduces the formation energy of sulfur vacancies (SV) in ZIS, thereby enhancing CO2 adsorption and activation. The SV-rich surface lowers the energy barrier for forming HCOO* to -0.33 eV whereas the energy barrier for forming *COOH is 0.77 eV. Successive hydrogenation of HCOO* leads to *CH2, which converts to *CH3 with an energy barrier of -0.63 eV. The energy barrier for *CH3-CH3 coupling is 0.54 eV, which is lower than the 0.73 eV for *CH2-CH2 coupling to form *C2H4. Thus, Z-M preferentially produces C2H6 over C2H4. Under visible light, Z-M achieves a CO2-to-C2H6 conversion rate of 467.3 µmol g-1 h-1 with 92.0% selectivity. This work highlights the dual role of plasmonic photocatalysts in enhancing CO2 adsorption and improving C2+ production in CO2 reduction.

Enhancing photocatalytic performance of covalent organic frameworks via ionic polarization

Covalent organic frameworks have emerged as a thriving family in the realm of photocatalysis recently, yet with concerns about their high exciton dissociation energy and sluggish charge transfer. Herein, a strategy to enhance the built-in electric field of series β-keto-enamine-based covalent organic frameworks by ionic polarization method is proposed. The ionic polarization is achieved through a distinctive post-synthetic quaternization reaction which can endow the covalent organic frameworks with separated charge centers comprising cationic skeleton and iodide counter-anions. The stronger built-in electric field generated between their cationic framework and iodide anions promotes charge transfer and exciton dissociation efficiency. Moreover, the introduced iodide anions not only serve as reaction centers with lowered H* formation energy barrier, but also act as electron extractant suppressing the recombination of electron-hole pairs. Therefore, the photocatalytic performance of the covalent organic frameworks shows notable improvement, among which the CH3I-TpPa-1 can deliver an high H2 production rate up to 9.21 mmol g−1 h−1 without any co-catalysts, representing a 42-fold increase compared to TpPa-1, being comparable to or possibly exceeding the current covalent organic framework photocatalysts with the addition of Pt co-catalysts.

Thermal characteristics of LiMnxFe1-xPO4 (x = 0, 0.6) cathode materials for safe lithium-ion batteries

Lithium-ion batteries have recently gained attention as energy storage devices due to their high energy densities and various applications. Layered Ni-Mn-Co-based cathode materials are widely used for their high energy density; however, their high cost necessitates the exploration of alternatives. Consequently, olivine-type LiMnxFe1-xPO4 materials are gaining popularity and are being increasingly adopted. While the synthesis methods and electrochemical properties of these materials have been extensively studied, thermal analyses remain limited. In this study, we investigated the thermal properties of olivine-type LiMnxFe1-xPO4 by combining thermal analysis, structural analysis, and computational calculations to evaluate the safety of lithium-ion batteries. Our results show that the formation energy of LiMn0.6Fe0.4PO4 is more stable than that of LiFePO4. As temperature increases, LiFePO4 decomposes at 350 °C, whereas LiMn0.6Fe0.4PO4 begins to decompose at 450 °C. The P-O bond plays a crucial role in the thermal stability of these materials; as the temperature rises, the thermal stability of the PO4 group diminishes, leading to structural decomposition. To enhance thermal stability, it is recommended to experiment with doping small amounts of various elements at the P site. This paper provides valuable insights for the design and development of thermally stable olivine-structured cathodes for lithium-ion batteries.

The Ordering and Arrangement of Intercalated Carboxylate Ions in Anion‐Exchangeable Layered Yttrium Hydroxides

AbstractThe intercalation chemistry is essential in the application of anion‐exchangeable layered metal hydroxides. However, much of the key information regarding intercalated anions, such as the degree of ordering and arrangement is still not clear or missing to date, due to the difficulty in probing the local environment of anions by routine characterization techniques. Herein, we employed solid‐state NMR (ssNMR) spectroscopy to offer valuable complementary insights into the ordering and arrangement of a series of monocarboxylate anions (RCOO−: R=HO, H, CH3, C2H5, and C3H7) within the interlayer space of two layered yttrium hydroxides (LYH‐Cl and LYH‐Br). The results imply that the two smaller carboxylate anions (R=HO and H) are disordered after intercalation, while the larger carboxylate anions (R=CH3, C2H5, and C3H7) are relatively ordered. We further explored if the intercalated anions are parallel arranged as those in sodium salts or antiparallel arranged as those predicted in the majority of previous reports. We uncovered that the intercalated anions are antiparallel arranged based on the formation energy obtained in density functional theory calculations and ssNMR data. Our results therefore contribute to a deeper and comprehensive understanding of the intercalation chemistry of layered rare earth hydroxides.

Improved gas sensing properties of copper-doped MoSe2 monolayers: a first-principles study on CO2 and NO2 adsorption

Abstract This paper investigates the impact of copper (Cu)-doped MoSe2 monolayer (ML) on gas sensing properties. The adsorption behaviour of CO2 and NO2 gas molecules on Cu-doped MoSe2 ML is reported and various sensing and electronic parameters such as adsorption energy, charge transfer and recovery time, are computed to delineate the adsorption characteristics and gas sensitivity. In our study, the doped Cu-atom in Se vacant MoSe2 ML shows the adsorption energies to be −1.32 eV (O-orient) and −1.72 eV (C-orient), for CO2, while for NO2, they are −0.879 eV (O-orient) and −1.06 eV (N-orient), respectively. The negative formation energy of −6.62 eV shows the electronic stability of Cu-doped MoSe2 ML and thermal stability, demonstrated by the molecular dynamics study through the Nose-Vervlet Thermostat (NVT) algorithm. Also, significant changes are observed in electronic conductivity and work function upon adsorbed Cu-MoSe2 ML. Lastly, these outcomes illustrate that Cu doping amplifies the capture ability of MoSe2 ML towards gas molecules, fostering improved electron interaction between the substrate surface and gas molecules, consequently enhancing its gas sensing ability.

Longitudinal Piezoelectricity and Polarization-Insensitive Oxidation in Janus vdWs Nb3SeI7.

As a newly discovered Janus van der Waals (vdW) material, semiconducting Nb3SeI7 offers several notable advantages, including spontaneous out-of-plane polarization, facile exfoliation to the monolayer limit, and significant out-of-plane emission dipole in second harmonic generation. These properties make it a promising candidate for piezoelectric and piezophototronic applications in highly efficient energy conversion. However, Nb3SeI7 is prone to oxidation when exposed to oxygen, which can severely limit the exploration and utilization of these intriguing physical properties. Therefore, understanding the oxidation mechanism of pristine Nb3SeI7 and its correlation with electrical polarization-an area that remains largely unexplored-is highly significant. In this study, the out-of-plane piezoelectricity of Nb3SeI7 is experimentally demonstrated, with a piezoelectric coefficient (|d33 eff|) of 0.76nmV-1. Furthermore, by combining near ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS), Time-of-Flight secondary ion mass spectrometry (ToF-SIMS), and Density functional theory (DFT)calculations, it is revealed that the oxidation of Nb3SeI7 is self-limiting and independent of its electrical polarization, owing to the similar defect formation energies of Se and I atoms. This self-limiting and polarization-insensitive oxidation provides valuable insights into the stabilization mechanisms and expands the potential applications of out-of-plane piezoelectricity and other intriguing physical properties in Janus vdW Nb3SeI7.

Engineering Co Single Atoms in Ultrathin BiOCl Nanosheets for Boosted CO2 Photoreduction

AbstractDespite the development of a range of photocatalysts for CO2 reduction, the practical applications are significantly limited by low conversion efficiencies and their reliance on sacrificial agents, which are rooted in thermodynamic and kinetic challenges related to CO2 conversion. Here, the engineering of Co single atoms in ultrathin single‐crystal BiOCl nanosheets for boosted photocatalytic CO2 reduction is reported. The engineering of Co atoms modulates the distribution of photogenerated charges at the catalyst surface, controlling key surface reaction dynamics and suppressing surface electron‐hole recombination. This modulation also improves light absorption and enhances CO2 adsorption and activation, leading to more efficient surface reactions. Notably, CO2 is stably adsorbed onto the (001) face of BiOCl through a Bi‐O‐C(= O)‐Co‐O coordination unit, which lowers the activation energy for CO2 reduction and reduces the formation energy of COOH− intermediates. As a result, the BiOCl photocatalysts achieve a CO formation rate of 183.9 µmol g−1 h−1, when irradiated with a 300 W Xe lamp without cocatalysts or sacrificial agents. It represents an ≈13‐fold increase compared to that of pristine BiOCl, and surpasses most reported Bi‐based photocatalysts to date. Current work provides valuable insights into engineering of single atoms for developing advanced CO2‐reduction photocatalysts.