Uncovering the crystal defects within aragonite CaCO3.

Knowledge of deformation mechanisms in aragonite, one of the three crystalline polymorphs of CaCO3, is essential to understand the overall excellent mechanical performance of nacres. Dislocation slip and deformation twinning were claimed previously as plasticity carriers in aragonite, but crystallographic features of dislocations and twins have been poorly understood. Here, utilizing various transmission electron microscopy techniques, we reveal the atomic structures of twins, partial dislocations, and associated stacking faults. Combining a topological model and density functional theory calculations, we identify complete twin elements, characters of twinning disconnection, and the corresponding twin shear angle (∼8.8°) and rationalize unique partial dislocations as well. Additionally, we reveal an unreported potential energy dissipation mode within aragonite, namely, the formation of nanograins via the pile-up of partial dislocations. Based on the microstructural comparisons of biogenic and abiotic aragonite, we find that the crystallographic features of twins are the same. However, the twin density is much lower in abiotic aragonite due to the vastly different crystallization conditions, which in turn are likely due to the absence of organics, high temperature and pressure differences, the variation in inorganic impurities, or a combination thereof. Our findings enrich the knowledge of intrinsic crystal defects that accommodate plastic deformation in aragonite and provide insights into designing bioengineering materials with better strength and toughness.

Highly scalable and flexible on-chip all-silicon mode filter using backward mode conversion gratings.

Mode filters are fundamental elements in a mode-division multiplexing (MDM) system for reducing modal cross-talk or realizing modal routing. However, the previously reported silicon mode filters can only filter one specific mode at a time and multiple modes filtering usually needs a cascade of several filters, which is adverse to highly integrated MDM systems. Here, we propose a unique concept to realize compact, scalable and flexible mode filters based on backward mode conversion gratings elaborately embedded in a multimode waveguide. Our proposed method is highly scalable for realizing a higher-order-mode-pass or band-mode-pass filter of any order and capable of flexibly filtering one or multiple modes simultaneously. We have demonstrated the concept through the design of four filters for different order of mode(s) and one mode demultiplexer based on such a filter, and the measurement of two fabricated 11µm length filters (TE1-pass/TE2-pass) show that an excellent performance of insertion loss <1.0dB/1.5dB and extinction ratio >29dB/28.5dB is achieved over a bandwidth of 51.2nm/48.3nm, which are competitive with the state-of-the-art.

A Ni-O-Ag photothermal catalyst enables 103-m2 artificial photosynthesis with >17% solar-to-chemical energy conversion efficiency.

The scalable artificial photosynthesis composed of photovoltaic electrolysis and photothermal catalysis is limited by inefficient photothermal CO2 hydrogenation under weak sunlight irradiation. Herein, NiO nanosheets supported with Ag single atoms [two-dimensional (2D) Ni1Ag0.02O1] are synthesized for photothermal CO2 hydrogenation to achieve 1065 mmol g-1 hour-1 of CO production rate under 1-sun irradiation. This performance is attributed to the coupling effect of Ag-O-Ni sites to enhance the hydrogenation of CO2 and weaken the CO adsorption, resulting in 1434 mmol g-1 hour-1 of CO yield at 300°C. Furthermore, we integrate the 2D Ni1Ag0.02O1-supported photothermal reverse water-gas shift reaction with commercial photovoltaic electrolytic water splitting to construct a 103-m2 scale artificial photosynthesis system (CO2 + H2O → CO + H2 + O2), which achieves more than 22 m3/day of green syngas with an adjustable H2/CO ratio (0.4-3) and a photochemical energy conversion efficiency of >17%. This research charts a promising course for designing practical, natural sunlight-driven artificial photosynthesis systems.

Surface Passivation to Enhance the Interfacial Pyro-Phototronic Effect for Self-Powered Photodetection Based on Perovskite Single Crystals.

The interfacial pyro-phototronic effect (IPPE) presents a novel approach for improving the performance of self-powered photodetectors (PDs) based on metal halide perovskites (MHPs). The interfacial contact conditions within the Schottky junctions are crucial in facilitating the IPPE phenomenon. However, the fabrication of an ideal Schottky junction utilizing MHPs is a challenging endeavor. In this study, we present a surface passivation method aimed at enhancing the performance of self-powered photodetectors based on inverted planar perovskite structures in micro- and nanoscale metal-halide perovskite SCs. Our findings demonstrate that the incorporation of a lead halide salt with a benzene ring moiety for surface passivation leads to a substantial improvement in photoresponses by means of the IPPE. Conversely, the inclusion of an alkane chain in the salt impedes the IPPE. The underlying mechanism can be elucidated through an examination of the band structure, particularly the work function (WF) modulated by surface passivation. Consequently, this alteration affects the band bending and the built-in field (VBi) at the interface. This strategy presents a feasible and effective method for producing interfacial pyroelectricity in MHPs, thus facilitating its potential application in practical contexts such as energy conversion and infrared sensors.

Cu-based high-entropy two-dimensional oxide as stable and active photothermal catalyst.

Cu-based nanocatalysts are the cornerstone of various industrial catalytic processes. Synergistically strengthening the catalytic stability and activity of Cu-based nanocatalysts is an ongoing challenge. Herein, the high-entropy principle is applied to modify the structure of Cu-based nanocatalysts, and a PVP templated method is invented for generally synthesizing six-eleven dissimilar elements as high-entropy two-dimensional (2D) materials. Taking 2D Cu2Zn1Al0.5Ce5Zr0.5Ox as an example, the high-entropy structure not only enhances the sintering resistance from 400 °C to 800 °C but also improves its CO2 hydrogenation activity to a pure CO production rate of 417.2 mmol g-1 h-1 at 500 °C, 4 times higher than that of reported advanced catalysts. When 2D Cu2Zn1Al0.5Ce5Zr0.5Ox are applied to the photothermal CO2 hydrogenation, it exhibits a record photochemical energy conversion efficiency of 36.2%, with a CO generation rate of 248.5 mmol g-1 h-1 and 571 L of CO yield under ambient sunlight irradiation. The high-entropy 2D materials provide a new route to simultaneously achieve catalytic stability and activity, greatly expanding the application boundaries of photothermal catalysis.

Ionic Covalent Organic Frameworks-Derived Cobalt Single Atoms and Nanoparticles for Efficient Oxygen Electrocatalysis.

Metal single atoms show outstanding electrocatalytic activity owing to the abundant atomic reactive sites and superior stability. However, the preparation of single atoms suffers from inexorable metal aggregation which is harmful to electrocatalytic activity. Here, ionic covalent organic frameworks (iCOFs) are employed as the sacrificial precursor to mitigate the metal aggregation and subsequent formation of bulky particles. Molecular dynamics simulation shows that iCOFs can trap and confine more Co ions as compared to neutral COFs, resulting in the formation of a catalyst composed of Co single atoms and uniformly distributed Co nanoparticles (CoSA &CoNP-10 ). However, the neutral COFs derive a catalyst composed of Co atomic clusters and large Co nanoparticles (CoAC &CoNP-25 ). The CoSA &CoNP-10 catalyst exhibits higher oxygen bifunctional electrocatalytic activities than CoAC &CoNP-25 , coinciding with the density functional theory results. Taking the CoSA &CoNP-10 as the air cathode in Zn-air batteries (ZABs), the aqueous ZAB presents a high power density of 181 mW cm-2 , a specific capacity of 811 mAh g-1 as well as a long cycle life of 407 h at a current density of 10 mA cm-2 , while the quasi-solid state ZAB displays a power density of 179 mW cm-2 and the cycle life of 30 h.

Unlocking the mysterious polytypic features within vaterite CaCO3.

Calcium carbonate (CaCO3), the most abundant biogenic mineral on earth, plays a crucial role in various fields such as hydrosphere, biosphere, and climate regulation. Of the four polymorphs, calcite, aragonite, vaterite, and amorphous CaCO3, vaterite is the most enigmatic one due to an ongoing debate regarding its structure that has persisted for nearly a century. In this work, based on systematic transmission electron microscopy characterizations, crystallographic analysis and machine learning aided molecular dynamics simulations with ab initio accuracy, we reveal that vaterite can be regarded as a polytypic structure. The basic phase has a monoclinic lattice possessing pseudohexagonal symmetry. Direct imaging and atomic-scale simulations provide evidence that a single grain of vaterite can contain three orientation variants. Additionally, we find that vaterite undergoes a second-order phase transition with a critical point of ~190 K. These atomic scale insights provide a comprehensive understanding of the structure of vaterite and offer advanced perspectives on the biomineralization process of calcium carbonate.

General heterostructure strategy of photothermal materials for scalable solar-heating hydrogen production without the consumption of artificial energy.

Solar-heating catalysis has the potential to realize zero artificial energy consumption, which is restricted by the low ambient solar heating temperatures of photothermal materials. Here, we propose the concept of using heterostructures of black photothermal materials (such as Bi2Te3) and infrared insulating materials (Cu) to elevate solar heating temperatures. Consequently, the heterostructure of Bi2Te3 and Cu (Bi2Te3/Cu) increases the 1 sun-heating temperature of Bi2Te3 from 93 °C to 317 °C by achieving the synergy of 89% solar absorption and 5% infrared radiation. This strategy is applicable for various black photothermal materials to raise the 1 sun-heating temperatures of Ti2O3, Cu2Se, and Cu2S to 295 °C, 271 °C, and 248 °C, respectively. The Bi2Te3/Cu-based device is able to heat CuOx/ZnO/Al2O3 nanosheets to 305 °C under 1 sun irradiation, and this system shows a 1 sun-driven hydrogen production rate of 310 mmol g-1 h-1 from methanol and water, at least 6 times greater than that of all solar-driven systems to date, with 30.1% solar-to-hydrogen efficiency and 20-day operating stability. Furthermore, this system is enlarged to 6 m2 to generate 23.27 m3/day of hydrogen under outdoor sunlight irradiation in the spring, revealing its potential for industrial manufacture.

Ambient sunlight-driven photothermal methanol dehydrogenation for syngas production with 32.9 % solar-to-hydrogen conversion efficiency.

Methanol dehydrogenation is an efficient way to produce syngas with high quality. The current efficiency of sunlight-driven methanol dehydrogenation is poor, which is limited by the lack of excellent catalysts and effective methods to convert sunlight into chemicals. Here, we show that atomically substitutional Pt-doped in CeO2 nanosheets (Pts-CeO2) exhibit excellent methanol dehydrogenation activity with 500-hr level catalytic stability, 11 times higher than that of Pt nanoparticles/CeO2. Further, we introduce a photothermal conversion device to heat Pts-CeO2 up to 299°C under 1 sun irradiation owning to efficient full sunlight absorption and low heat dissipation, thus achieving an extraordinarily high methanol dehydrogenation performance with a 481.1 mmol g-1 h-1 of H2 production rate and a high solar-to-hydrogen (STH) efficiency of 32.9%. Our method represents another progress for ambient sunlight-driven stable and active methanol dehydrogenation technology.

9.2%-efficient core-shell structured antimony selenide nanorod array solar cells.

Antimony selenide (Sb2Se3) has a one-dimensional (1D) crystal structure comprising of covalently bonded (Sb4Se6)n ribbons stacking together through van der Waals force. This special structure results in anisotropic optical and electrical properties. Currently, the photovoltaic device performance is dominated by the grain orientation in the Sb2Se3 thin film absorbers. Effective approaches to enhance the carrier collection and overall power-conversion efficiency are urgently required. Here, we report the construction of Sb2Se3 solar cells with high-quality Sb2Se3 nanorod arrays absorber along the [001] direction, which is beneficial for sun-light absorption and charge carrier extraction. An efficiency of 9.2%, which is the highest value reported so far for this type of solar cells, is achieved by junction interface engineering. Our cell design provides an approach to further improve the efficiency of Sb2Se3-based solar cells.

In situ tracking the reversible spinel-rocksalt structural transformation between Mn3O4 and MnO.

Electron beam irradiation is well known to induce damage in materials. The structural transformation involved in the damage is usually believed to be an irreversible solid state chemical reaction. Here we use in situ transmission electron microscopy (TEM) combined electron-energy loss spectroscopy (EELS) technique in an aberration-corrected TEM to track the structural transformation in spinel Mn3O4 induced by electron beam irradiation. It is clarified that spinel Mn3O4 is transformed to rocksalt structured MnO by irradiation and the reversed recovering transition from rocksalt MnO to spinel Mn3O4 can occur by aging in the gentle electron beam circumstance. The mechanisms including the role of O desorption/adsorption and the displacement of Mn and O involved in the reversible transformation processes are discussed. The work presents an implication that electron beam can modify the structure at atomic dimension yielding diverse assemblies of surfaces, interfaces and colorful properties.

Band alignment and enhanced photocatalytic activation of α/ß-Bi2O3 heterojunctions via in situ phase transformation.

The assembling heterojunction, one of the key topics in photocatalysts and semiconductors (SCs), is generally accomplished in at least two steps, of which the first step is the synthesis of a matrix, and then the growth of the second phase on the matrix. Herein we present the preparation of α/ß-Bi2O3 heterojunctions by an in situ phase transformation technique. Under normal pressure, a facile citrate method was used to synthesize ß-Bi2O3 nanosheets and α/ß-Bi2O3 heterojunctions. The novel features of the process are the mild operating conditions by an appropriate selection of heat treatment temperature and time. Using transmission electron microscopy (TEM), we found that a number of nano-sized α-Bi2O3 form on the ß-Bi2O3 nanosheet via a controlled ß→α phase transition, generating a large number of heterojunctions. The CM1 (calcining ß-Bi2O3 precursor at 363 °C for 4 h) heterojunction achieves a strong visible light absorption and dye absorption capacity and produces a very high reaction rate for Rhodamine B (RhB) photodegradation. Electrochemical impedance spectroscopy (EIS) revealed excellent charge transfer characteristics of the heterojunction, which accounts for its high photoactivity. Using the X-ray electron valence band spectra, it is found that the valence band of α-Bi2O3 is more negative than that of ß-Bi2O3. Thus, in heterojunctions, the photogenerated holes in ß-Bi2O3 are transferred to α-Bi2O3 with good charge transport characteristics by the intrinsic driving force in the interface field. Furthermore, a separated hole can accomplish a transfer process from α-Bi2O3 to the aqueous solution within its lifetime due to the diameter of α-Bi2O3 being less than 17.6 nm.