Stable Crystals Research Articles

Polymorphic Crystallization Behavior of a Poly(butylene adipate) Midblock within a Poly(L-lactide-butylene adipate-L-lactide) Triblock Copolymer.

New biodegradable aliphatic PLLA-PBA-PLLA copolymers with soft poly(butylene adipate) (PBA) and hard poly(l-lactide) (PLLA) building blocks were synthesized via ring-opening polymerization (ROP). Proton nuclear magnetic resonance (1HNMR) was utilized to confirm the volume fraction of PBA (fPBA) within PLLA-PBA-PLLA. It was found that a PBA midblock (PBA-mid) within PLLA-PBA-PLLA-s (PLLA-PBA-PLLA triblock copolymer with a short PLLA block length) might display lamellar domain structure. However, PBA-mid within PLLA-PBA-PLLA-l (PLLA-PBA-PLLA triblock copolymer with a long PLLA block length) might locate itself as a nanoscale cylindrical domain surrounded by a PLLA continuous phase. Polymorphic crystals of PBA-mid within the PLLA-PBA-PLLA copolymers were formed after melt crystallization at the given temperatures, which were studied by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) analysis. According to the WAXD and DSC analyses, it was interesting to find that the α-type crystal of PBA-mid was favorable to develop in the lower temperature region regardless of the state (crystallization or amorphous) of the PLLA component. Additionally, when the PLLA component was held in its amorphous state, it was easier for PBA-mid within the PLLA-PBA-PLLA copolymers to transform from the metastable β-form crystal to the stable α-form crystal. Furthermore, polarized optical microscopy (POM) photos provided direct evidence of the polymorphic crystals of PBA-mid within PLLA-PBA-PLLAs.

Intrinsic Phase Stability and Inherent Bandgap of Formamidinium Lead Triiodide Perovskite Single Crystals.

Understanding the intrinsic phase stability and inherent band gap of formamidinium lead triiodide (FAPbI3 ) perovskites is crucial to further improve the performance of perovskite solar cells (PSCs). Herein, we explored the α- to δ-phase transition and band gap of FAPbI3 single crystals grown by an inverse temperature solubility method. We found that the residual γ-butyrolactone solvents in the inner empty space of the FAPbI3 single crystal accelerate the phase transition at kinetics. By adopting 2-methoxyethanol as the solvent, over 2000 h of stable α-FAPbI3 crystals could be acquired. This proves that although FAPbI3 is regarded as unstable at thermodynamics, it could own excellent kinetic stability without any doping or additives because of the slow solid to solid phase transition instead of the fast phase transition assisted by the solvents. Furthermore, we revealed that the bulk FAPbI3 single crystal with a size above 100 μm can have an inherent band gap of 1.41 eV. Thus, our work provides key scientific guidance for high-performance FAPbI3 -based PSCs.

Evaluation of corrosion resistance, mechanical integrity loss and biocompatibility of PCL/HA/TiO2 hybrid coated biodegradable ZM21 Mg alloy

A novel PCL/HA/TiO 2 hybrid coating on ZM21 Mg alloy substrate has been investigated for corrosion resistance, biocompatibility and mechanical integrity loss in terms of bending, compressive and tensile strength in physiological media. The prepared hybrid coating was dip coated over ZM21 from HA/TiO 2 and PCL solutions followed by creating a microporous PCL layer by utilizing Non-solvent Induced Phase Separation (NIPS) technique. The electrochemical measurement and in-vitro degradation study in SBF after 28 days showed that the PCL/HA/TiO 2 hybrid coating reduced H2 evolution rate, weight loss, and corrosion rate by 64, 116 and 118 times respectively, as compared to uncoated ZM21 samples. The surface studies carried out using SEM-EDX, FTIR and XRD revealed formation of highly stable 3d flower-like HA crystals with Ca/P ratio of 1.60 in the PCL micropores. This dense apatite growth effectively protected the PCL/HA/TiO 2 hybrid coated samples to maintain the good mechanical integrity even after 28 days of immersion as compared to HA/TiO 2 composite coated, As-polished (A/P) and As-machined (A/M) samples. The failure analysis of samples under mechanical loading were performed using SEM-BSE-EBSD. The in-vitro cellular viability of L929 fibroblast cells on PCL/HA/TiO 2 hybrid coating was found 50.47% higher with respect to control group, whereas bacterial viability was supressed by 57.15 and 62.35% against gram-positive Staphylococcus aureus and gram-negative Escherichia coli bacterial models. The comprehensive assessment indicates PCL/HA/TiO 2 hybrid coating as a suitable candidate to delay early degradation and mechanical integrity loss of Mg-based alloys for devising biodegradable orthopaedic implant.

A ternary MnO/MnTiO3@C composite anode with greatly enhanced cycle stability for Li-ion batteries

Manganese monoxide (MnO) has been widely studied as a potential anode material of Li-ion batteries because of its high specific capacity and abundant raw materials. However, the poor cycling stability of MnO associating to its large volume change during the repeated conversion reaction with Li+ has restricted its practical applications. Herein, ternary MnO/MnTiO3@C composite anode materials are prepared by in situ capturing TiO2 nanoparticles into sea urchin-like MnO2 in a mild hydrothermal reaction, followed by resorcinol-formaldehyde (RF) resin coating and thermal treatment. With the strong stabilization effect of the MnTiO3 component, the optimized ternary MnO/MnTiO3@C composite anode exhibits greatly enhanced cycling performance as compared to MnO@C. A reversible capacity of 383 mAh g−1 is preserved after 500 cycles at 1000 mA g−1. This improved cycle performance can be originated from the stable TiO crystals and the highly reversible amorphous LixMnTiO3 phase generated in the first lithiation process. The reasonably high specific capacity and robust cycle stability enable the ternary MnO/MnTiO3@C composites to be promising alternative anode materials to graphite for Li-ion batteries.

Preparation of Acrylic Yarns with Durable Structural Colors Based on Stable Photonic Crystals.

Structural coloration of photonic crystals (PCs) is considered an ecological and environmental way to achieve colorful textiles. However, constructing PCs with obvious structural colors on traditional flexible yarns is still a great challenge. As a secondary structure that forms textiles, compared with fibers and fabrics, the yarns are rougher, hindering the construction of regular PCs. In this work, the flexible acrylic yarns with vivid structural colors, named PC-based structural color yarns, were prepared by constructing regular PCs via assembling poly(styrene-butyl acrylate-methacrylate) (P(St-BA-MAA)) colloidal microspheres on yarns. Specifically, the properties of P(St-BA-MAA) colloidal microspheres were investigated. The PCs with better structural stability and obvious structural colors were prepared by presetting the acrylic adhesive layer on yarns. Moreover, the color durability and color regulation methods of prepared PC-based structural color yarns were evaluated and discussed. The results showed that the P(St-BA-MAA) colloidal microspheres exhibited even particle sizes, excellent monodispersity, and a typical hard core-soft shell structure. And the glass-transition temperature (T g) of the microspheres was tested to be about 65.6 °C. The cationic acrylate regarded as a pretreatment agent could not only improve the combination between the PC layers and the yarns by acting as a "bridge" but also enhance the structural color effect by smoothing the yarn surface. The results showed that when the mass fraction of cationic acrylate was 3 wt %, the microspheres were beneficial to access regular PCs with obvious structural colors. The PCs with bright structural colors could be constructed on black acrylic yarns, and the colors of yarns were still bright after rubbing and washing tests, indicating that the prepared PC-based structural color yarns have good color fastness. Moreover, the color hue of PC-based structural color yarns could be regulated by adjusting the particle sizes and viewing angles. This study provides strategic support for the structural coloration of flexible materials.

A novel matrix protein PNU5 facilitates the transformation from amorphous calcium carbonate to calcite and aragonite

For both nacre formation and biomineralization in mollusks, understanding the molecular mechanism is imperative. Biomineralization, especially shell formation, is dedicatedly regulated by multiple matrix proteins. However, ACC conversion to stable crystals still lacks positive factors. In this research, we found a novel matrix protein named PNU5 in Pinctada fucata that plays a regulatory role in both prismatic layer and nacreous layer formation. Functional studies in vivo and in vitro have shown that it might be involved in shell formation in a positive manner. RT-qPCR analysis showed that pnu5 was highly expressed in mantle pallial and participated in shell repairing and regeneration. RNAi-mediated repression of pnu5 could affect the normal structure of prismatic layer and nacreous layer. The recombinant protein rPNU5 significantly enhanced the precipitation rate of CaCO3 both in the calcite and aragonite crystallization systems, as well as altering the morphology of the crystals. Based on ACC transition experiments, the recombinant protein rPNU5 facilitated amorphous calcium carbonate (ACC) transformation into stable calcite or aragonite. This study could provide us with a better understanding of how positive regulatory mechanisms contribute to biomineralization.

(Digital Presentation) MOCVD Growth of Ga2O3, Algao and Heterostructures

Ultrawide bandgap (UWBG) gallium oxide (Ga2O3) represents an emerging semiconductor material with excellent chemical and thermal stability. It has a band gap of 4.5-4.9 eV, much wider than that of the GaN (3.4 eV) and 4H-SiC (3.2 eV). The monoclinic β-phase Ga2O3 represents the thermodynamically stable crystal among the known five known phases (α, β, γ, d, ε/κ). The breakdown field of β-Ga2O3 is predicted to be 6-8 MV/cm, which is much larger than that of the 4H-SiC and GaN. These unique properties make β-Ga2O3 a promising candidate for high power electronic device and solar blind photodetector applications. Single crystal β-Ga2O3 substrates can be synthesized by scalable and low cost melting based growth techniques. Metalorganic chemical vapor deposition (MOCVD) growth technique was demonstrated to produce high quality β-Ga2O3 thin films and its ternary (AlxGa1-x)2O3 alloys. Control of background and n-type doping in β-Ga2O3 will be discussed. Record carrier mobilities of 194 cm2/V·s at room temperature and ~10,000 cm2/V·s at low temperature were measured for MOCVD β-Ga2O3 thin films. Growth and fundamental understanding of β-(AlxGa1-x)2O3 are still limited. The incorporation of Al in beta-phase Ga2O3 has not been well understood, although it was predicted up to 60% of Al composition could be incorporated into β-Ga2O3. MOCVD growth of β-AlGaO targeting for Al composition of > 40% will be discussed. N-type doping capability as a function of Al composition in (AlxGa1-x)2O3 is another important fundamental question. Charge carrier transport properties in (AlxGa1-x)2O3 will be discussed. In addition, MOCVD growth of different phases of Ga2O3 and AlGaO will be presented. Acknowledgement: The authors acknowledge the funding support from the Air Force Office of Scientific Research FA9550-18-1-0479 (AFOSR, Dr. Ali Sayir) and the National Science Foundation (1810041, 2019753, 1755479).

One step to stabilize calcium sodium phosphate crystals acting as photocatalysts embedded in a glass matrix

Unstable calcium sodium phosphate (CaNaPO4) in aqueous solution can be stabilized and shows photocatalytic activity in a glass matrix. This research utilizes one-step melt quenching to prepare glass ceramics with stable CaNaPO4 crystals in a glass material. The photocatalytic activity of the CaNaPO4 glass ceramic was investigated by monitoring methyl orange degradation with the addition of H2O2. Notably, the CaNaPO4 glass ceramic demonstrates the high-efficiency photocatalytic degradation of methyl orange (MO) under UV irradiation. The CaNaPO4 glass ceramic could be reused several times. After 8 cycles, the catalyst was still stable and effective in decomposing 100% of methyl orange within 5 h/cycle. In addition, the solid phase photocatalytic activity of the CaNaPO4 glass ceramic was examined by bleaching adsorbed MB under UV light for 25 h. It could also inhibit the growth of E. coli bacteria after UV irradiation for 20 min. Therefore, CaNaPO4 embedded glass ceramic might be an alternative photocatalytic material for wastewater treatment.

Releasable Water Charge-Trapping and Water-Resistant Photodetection using 1D Perovskitoid Hydrate Single Crystal.

Hydrates of hybrid organic-inorganic perovskites have been discovered with MAPbI3 and are proved to be unstable in atmosphere. However, the influence of water molecules on the performance of optoelectronic devices is still not fully understood. Here, using a dication, 2-(dimethylamino) ethylamine (DMEN2+ ), a stable quasi-1Dperovskitoid hydrate single crystal is designed and successfully synthesized, which is formulated as DMENPb2 I6 ·H2 O. In this design, both corner-sharing and edge-sharing connectivity are adopted, and water molecules are connected with the crystal through hydrogen bonding. It is discovered that such water sites distributed along the inorganic chains function both as charge traps and as releasable charge stocks. Optical excitation that overcomes the potential wells formed on these water sites may release these stocked charges and facilitate enhanced transportable charge density. Meanwhile, exciton diffusion and charge transport are strongly confined in the 1D transport channels. Above mechanisms are verified both by the transient absorption spectroscopy and by the photodetection performance. This introduces a new design strategy with a trapping-stock-releasing-transport roadmap for perovskitoid materials. Excellent water resistance endows this material with more advantages in the development of a new generation of optoelectronic devices.

Mechanical stability of fluorinated-methane clathrate hydrates

• Lattice constant of clathrate hydrates formed by encapsulating fluorinated methane derivatives is greatly dictated by the number of fluorine atoms. • Polar fluorinated methane derivatives@cage show distinct rotational dynamics that vary with global strain. • Mechanical properties of clathrate hydrates are greatly influenced by the size and dipole moment of guests. • Unconventional water cages form as clathrate hydrates are mechanically failed via fractures of water cages. Clathrate hydrates recently find important practical applications in the capture and recovery of greenhouse gases, cold storage and refrigeration systems. Nevertheless, their properties at microscopic scale remains largely insufficient yet. Herein, the structure and stability of clathrate hydrates encapsulating fluorinated methane derivatives under mechanical load are investigated by molecular dynamics simulations. All investigated clathrate hydrates are structurally stable host-guest molecular crystals yet show distinct structural and mechanical behaviors. Lattice constant of those clathrate hydrates is dictated by the size and dipole moment of fluorinated methane, for example, it is initially enlarged with increasing fluorine atom in the methane guest molecule but followed by reduction as the guest molecule becomes tetrafluoromethane. However, clathrate hydrates encapsulating non-polar fluorinated methane show superior mechanical properties over those encapsulating polar ones. Polar fluorinated methane derivatives@clathrate cages exhibit distinct rotational dynamics that are influenced by strain. Moreover, all studied clathrate hydrates are mechanically failed by fractures of water cage accompanied by formation of unconventional clathrate cages. Those findings give insights into understanding the structural, thermodynamic stability and mechanical properties of clathrate hydrates encapsulating fluorinated guests.

Atomic-Scale Tracking of Dynamic Nucleation and Growth of an Interfacial Lead Nanodroplet.

Revealing the evolutional pathway of the nucleation and crystallization of nanostructures at the atomic scale is crucial for understanding the complex growth mechanisms at the early stage of new substances and spices. Real-time discrimination of the atomic mechanism of a nanodroplet transition is still a formidable challenge. Here, taking advantage of the high temporal and spatial resolution of transmission electron microscopy, the detailed growth pathway of Pb nanodroplets at the early stage of nucleation was directly observed by employing electron beams to induce the nucleation, growth, and fusion process of Pb nanodroplets based on PbTiO3 nanowires. Before the nucleation of Pb nanoparticles, the atoms began to precipitate when they were irradiated by electrons, forming a local crystal structure, and then rapidly and completely crystallized. Small nanodroplets maintain high activity and high density and gradually grow and merge into stable crystals. The whole process was recorded and imaged by HRTEM in real time. The growth of Pb nanodroplets advanced through the classical path and instantaneous droplet coalescence. These results provide an atomic-scale insight on the dynamic process of solid/solid interface, which has implications in thin-film growth and advanced nanomanufacturing.

The advantages of microwave in using engineering spoil to sinter bricks

The difference in process parameters and sintering mechanism between microwave sintering and conventional sintering is studied in this thesis. The muffle furnace is adopted to simulate the conventional sintering. The engineering spoil is used as the raw material to prepare green bodies with different water-material ratios. By testing the weight loss on ignition, sintering shrinkage, water absorption, compressive strength, microstructure and crystalline composition of spoil bricks with different water-material ratios, the effects of the two sintering technologies on the performance of spoil bricks were compared to reach the best solution. The sintering mechanism of spoil bricks in CS and MWS was discussed through linear regression analysis. Through leaching toxicity analysis, the leaching toxicity of raw materials and spoil bricks was tested. The results show that compared with CS, MWS has higher efficiency on ignition, lower energy consumption, and better fixation effect on toxic metal elements. The MWS bricks have greater weight loss on ignition, sintering shrinkage and compressive strength, and lower water absorption. Both technologies will transform the mineral crystals in the raw materials into more stable crystals with basically the same composition through phase change. But the microstructure of the spoil bricks using MWS is denser. Besides, as the moisture content of the green bodies increases, the sintering efficiency of MWS will decrease, while the reverse is true for CS. With the increase of the water-material ratio, the weight loss on ignition and water absorption of MWS and CS bricks will increase, but the sintering shrinkage rate and compressive strength will decrease. In summary, MWS, with a better comprehensive performance, is more efficient and energy-saving than CS, the optimal forming water-material ratio for MWS technology is 0.14.

Predicted Pressure-Induced High-Energy-Density Iron Pentazolate Salts

Metal-pentazolate compounds as candidates for novel high-energy-density materials have attracted extensive attention in recent years. However, dehydrated pentazolate salts of transition metal iron are rarely reported. We predict two new iron pentazolate salts Fdd2-FeN10 and (No.1)-FeN10 using a constrained crystal search method based on first-principles calculations. We propose that the stable Fdd2-FeN10 crystal may be synthesized from FeN and N2 above 20 GPa, and its formation enthalpy is lower than the reported iron pentazolate salt (marked as (No.2)-FeN10). Crystal (No.1)-FeN10 is composed of iron bispentazole molecules. Formation enthalpy, phonon spectrum and ab initio molecular dynamics calculations are performed to show their thermodynamic, mechanical and dynamic properties. Moreover, the high energy density (3.709 kJ/g, 6.349 kJ/g) and good explosive performance indicate their potential applications as high-energy-density materials.

Influence on crystal nucleation of an order-disorder transition among the subcritical clusters.

Studies of nucleation generally focus on the properties of the critical cluster, but the presence of defects within the crystal lattice means that the population of nuclei necessarily evolve through a distribution of precritical clusters with varying degrees of structural disorder on their way to forming a growing stable crystal. To investigate the role precritical clusters play in nucleation, we develop a simple thermodynamic model for crystal nucleation in terms of cluster size and the degree of cluster order that allows us to alter the work of forming the precritical clusters without affecting the properties of the critical cluster. The steady state and transient nucleation behavior of the system are then studied numerically, for different microscopic ordering kinetics. We find that the model exhibits a generic order-disorder transition in the precritical clusters. Independent of the types of ordering kinetics, increasing the accessibility of disordered precritical clusters decreases both the steady state nucleation rate and the nucleation lag time. Furthermore, the interplay between the free-energy surface and the microscopic ordering kinetics leads to three distinct nucleation pathways.

Binary isobaric phase diagrams of stearyl alcohol-poloxamer 407 formulations in the molten and solid state

Multiparticulate formulations allow for the design of specialized pharmaceutical dosage forms that cater to the needs of a wide range of patient demographics, such as pediatric and geriatric populations, by affording control over the release rate and facilitating the formulation of fixed-dose combination drugs. Melt spray-congealing (MSC) is a method for preparing multiparticulate dosage forms from a suspension or solid solution of active pharamaceutical ingredients (API) and a molten carrier matrix. Stearyl alcohol and poloxamer 407 mixtures are widely used as carrier matrices in MSC microsphere formulations. In this report, the phase equilibria of stearyl alcohol-poloxamer 407 mixtures were investigated by generating binary phase diagrams of composition, i.e. weight/weight percent of poloxamer 407 in stearyl alcohol, and temperature in the molten form and the solid state. The phase equilibria of the molten state were characterized by 1H NMR measurements. The miscibility curves of stearyl alcohol-poloxamer 407 molten mixtures revealed that stearyl alcohol and poloxamer 407 are not miscible in all proportions and that miscibility substantially increases with temperature. The phase equilibria of the solid state were characterized by DSC and PXRD experiments. The phase diagrams of the solid state indicate that stearyl alcohol and poloxamer 407 crystallize and melt separately and, thus, do not form a eutectic or a single phase. The phases equilibria of the bulk mixtures were compared to the phases observed in placebo MSC microspheres and it was determined that the microspheres consist of a mixture of thermodynamically stable and metastable stearyl alcohol crystals immediately after manufacture.

Search for stable skyrmion lattices at the ground state in a multiferroic nanofilm using artificial neural networks

Magnetoelectric nanofilms are of great interest as functional elements of ultra-dense memory cells. In the ground state they may contain various topological magnetic vortex structures of several nanometers in size. The qualitative and quantitative properties of such structures strongly depend on a set of physical parameters. To calculate the ground state configuration with given parameters, we use the steepest descent method. However, to study a large parametric space significant computational resources are required. To solve this problem, we propose the use artificial neural networks (ANN), which can help us uncover the relationship between combinations of parameters and the corresponding ground state configurations using a relatively small number of pre-computed configurations as the training data. The application of the ANN allows one to avoid excessive computational costs in the study of the parametric space and narrow down the parametric area in which the existence of stable non-trivial ground state configurations in the form of a stable skyrmion crystal is possible.

Investigation on mineralization performance and spore germination conditions of calcium carbonate mineralizing bacteria

Microbial induced calcium carbonate precipitation (MICP) provides a theoretical basis for repairing underground rocks. The optimal germination conditions and mineralization activities of Bacillus pasteurii with crack repair function were investigated. The growth and mineralization properties of microorganisms in different environments were explored by measuring the urease activity and calcium carbonate production of bacteria, and the influencing factors of bacterial biomass and urease activity were analyzed. The microscopic morphology of bacterial mineralization products was analyzed by SEM, XRD and TG-DSC test. The influencing factors of spore germination rate were studied by measuring the OD value of spore germination. The results showed that under the conditions of pH 7.3, urea concentration 0.25–0.5 mol l−1, and calcium ion concentration 0.4–0.6 mol l−1, the mineralization activity of B. pasteurii was the strongest, and the generated mineralization product was a stable calcite crystal. The optimum concentration of germination agent and inorganic salt were 10 mmol l−1 and 200 mmol l−1, respectively.

A cost-effective approach to recycle serpentine tailings: Destruction of stable layered structure and solvent displacement crystallization

In this work, the stable layer structure of serpentine, which seriously restricts the extraction of magnesium, was broken down, and a nearly 94% leaching efficiency of Mg was obtained by adding 5% fluorite powder. Compared with the system without fluorite, the Mg leaching efficiency increased by 36.42%. This result was achieved because the complexation of fluorinion (F − ) with Si in serpentine promoted a distorted tetrahedral orientation, which led to a loose crystal structure of serpentine and contributed to exposing more Mg for a remarkable increase in Mg recovery. It is suggested that fluorite powder could replace expensive assisted reagents in the leaching process, which would markedly decreased the cost. Moreover, an energy-efficient “solvent displacement crystallization” (SDC) method was employed to efficiently recover magnesium (99.04%) from pregnant solutions. At the same time, the reuse of fluorine-containing solutions was explored.

Unraveling the irreversible transformation by nucleophilic substitution: A hint for fully transparent perovskite

AbstractMethylamine molecular treatment (MMT) either in precursor ink or final film of perovskite has been widely proposed to trigger either high‐efficiency, room‐temperature, green‐solvent, fast crystallization, and high‐throughput in processing perovskite solar cells but exclusively limited in methylammonium (MA)‐based perovskites, which is due to the reversible exchange between external methylamine (MA0) molecule and the same molecule's cation form (MA+) in the crystallographic A‐site of MA‐based perovskites. Executing MMT into formamidinium (FA)‐based perovskite (e.g., FAPbI3) that has optimal electronic band structure may bring new insights not only in high‐quality FAPbI3 towards higher efficiency but also in manufacturing merits such as fast and low‐temperature processability. By this motivation, we introduced MMT into the processing of FAPbI3 but obtained a new stabilized bleached crystal with complete transparency in the visible range. This can be ascribed to the irreversible reaction between the external MA0 molecule and the larger‐size FA+ cation in the lattice. We systematically investigated the chemical interaction in the MMT‐FAPbI3 system and proposed a nucleophilic substitution mechanism to understand this irreversible transformation. Surprisingly, this highly stable transparent crystal exhibits high transparency with average visible transmission (AVT) of 77.07% and color rendering index (CRI) of 95.81, and shows promising photodetector performance with response time less than 2 ms and on/off ratio of 1.18 × 103 under ultraviolet (UV) radiation, providing a novel and stable transparent candidate for UV photodetector application.image

1T′-MoTe2 monolayer: A promising two-dimensional catalyst for the electrochemical production of hydrogen peroxide

The direct synthesis of hydrogen peroxide (H2O2) via a two-electron oxygen reduction reaction (2e-ORR) in acidic media has emerged as a green process for the production of this valuable chemical. However, such an approach employs expensive noble-metal-based electrocatalysts, which severely undermines its feasibility when implemented on an industrial scale. Herein, based on density functional theory computations and microkinetic modeling, we demonstrate that a novel two-dimensional (2D) material, namely a 1T′-MoTe2 monolayer, can serve as an efficient non-precious electrocatalyst to facilitate the 2e-ORR. The 1T′-MoTe2 monolayer is a stable 2D crystal that can be easily produced through exfoliation techniques. The surface-exposed Te sites of the 1T′-MoTe2 monolayer exhibit a favorable OOH* binding energy of 4.24 eV, resulting in a rather high basal plane activity toward the 2e-ORR. Importantly, kinetic computations indicate that the 1T'-MoTe2 monolayer preferentially promotes the formation of H2O2 over the competing four-electron ORR step. These desirable characteristics render 1T′-MoTe2 a promising candidate for catalyzing the electrochemical reduction of O2 to H2O2.