Oxygen Vacancies Trigger Rapid Charge Transport Channels at the Engineered Interface of S-Scheme Heterojunction for Boosting Photocatalytic Performance.

Although oxygen vacancies (Ovs) have been intensively studied in single semiconductor photocatalysts, exploration of intrinsic mechanisms and in-depth understanding of Ovs in S-scheme heterojunction photocatalysts are still limited. Herein, a novel S-scheme photocatalyst made from WO3-Ov/In2S3 with Ovs at the heterointerface is rationally designed. The microscopic environment and local electronic structure of the S-scheme heterointerface are well optimized by Ovs. Femtosecond transient absorption spectroscopy (fs-TAS) reveals that Ovs trigger additional charge movement routes and therefore increase charge separation efficiency. In addition, Ovs have a synergistic effect on the thermodynamic and kinetic parameters of S-scheme photocatalysts. As a result, the optimal photocatalytic performance is significantly improved, surpassing that of single component WO3-Ov and In2S3 (by 35.5 and 3.9 times, respectively), as well as WO3/In2S3 heterojunction. This work provides new insight into regulating the photogenerated carrier dynamics at the heterointerface and also helps design highly efficient S-scheme photocatalysts.

Mitigating Lattice Distortion of High-Voltage LiCoO2 via Core-Shell Structure Induced by Cationic Heterogeneous Co-Doping for Lithium-Ion Batteries.

Inactive elemental doping is commonly used to improve the structural stability of high-voltage layered transition-metal oxide cathodes. However, the one-step co-doping strategy usually results in small grain size since the low diffusivity ions such as Ti4+ will be concentrated on grain boundaries, which hinders the grain growth. In order to synthesize large single-crystal layered oxide cathodes, considering the different diffusivities of different dopant ions, we propose a simple two-step multi-element co-doping strategy to fabricate core-shell structured LiCoO2 (CS-LCO). In the current work, the high-diffusivity Al3+/Mg2+ ions occupy the core of single-crystal grain while the low diffusivity Ti4+ ions enrich the shell layer. The Ti4+-enriched shell layer (~ 12 nm) with Co/Ti substitution and stronger Ti-O bond gives rise to less oxygen ligand holes. In-situ XRD demonstrates the constrained contraction of c-axis lattice parameter and mitigated structural distortion. Under a high upper cut-off voltage of 4.6 V, the single-crystal CS-LCO maintains a reversible capacity of 159.8 mAh g-1 with a good retention of ~ 89% after 300 cycles, and reaches a high specific capacity of 163.8 mAh g-1 at 5C. The proposed strategy can be extended to other pairs of low- (Zr4+, Ta5+, and W6+, etc.) and high-diffusivity cations (Zn2+, Ni2+, and Fe3+, etc.) for rational design of advanced layered oxide core-shell structured cathodes for lithium-ion batteries.

General Synthesis of Single-Crystal Spinel Cathodes with the Tailored Orientation of Exposed Crystal Planes for Advanced Lithium-Ion Batteries.

The spinel Mn-based cathodes with 3D Li+ diffusion channels, high voltage, and low-cost show promise for developing high-power lithium-ion batteries (LIBs). But the disproportionation and Jahn-Teller distortion lead to structural degeneration and capacity decay, especially at high working temperatures. Herein, considering the merits of single crystals and orientation of exposed crystal planes, single-crystal truncated octahedral LiMn2 O4 (TO-LMO) with exposed {111}, {100} and {110} facets is rationally designed, in which the mainly exposed {111} facets are truncated by a small portion of {100} and {110} facets. The Li-deficient intermediate phase is innovatively proposed to prepare the single-crystal TO-LMO. The synergistic effects of single crystals and the orientation of exposed crystal planes significantly reduce the disproportionation of Mn3+ ions and thereby improve their structural stability. Consequently, the cycling stability of the single-crystal TO-LMO is remarkably enhanced, obtaining outstanding capacity retention of 84.3% after 2000 cycles, much better than that of 61.2% for octahedral LiMn2 O4 . The feasibility of preparing single-crystal truncated octahedral LiNi0.5 Mn1.5 O4 with exposed {111}, {100}, and {110} facets via the Li-deficient intermediate phase is further demonstrated. These findings offer new insight into regulating the orientation of exposed crystal planes and improving the reversibility of Mn-based redox couples in LIBs.

A thermodynamically stable O2-type cathode with reversible O2-P2 phase transition for advanced sodium-ion batteries.

Low-cost sodium-ion batteries (SIBs) have shown very promise in the applications of renewable energy and low-speed electric vehicles. The development of a new O2-type cathode in SIBs is very challenging in that this compound is only stable as an intermediate product of P2-type oxides during redox reactions. Here, we report a thermodynamically stable O2-type cathode obtained by Na/Li ion exchange from P2-type oxide in a binary molten salt system. It is demonstrated that the as-prepared O2-type cathode exhibits a highly reversible O2-P2 phase transition during Na+ de-intercalation. The unusual O2-P2 transition has a low volume change of ∼11%, much lower than that of 23.2% for P2-O2 transformation in the P2-type cathode. The lowered lattice volume change of this O2-type cathode gives rise to superior structural stability upon cycling. Therefore, the O2-type cathode possesses a reversible capacity of about 100 mAh/g with a good capacity retention of 87.3% even after 300 cycles at 1C, indicating outstanding long-term cycling stability. These achievements will promote the development new class of cathode materials with high capacity and structural stability for advanced SIBs.

Supported Ruthenium Single-Atom and Clustered Catalysts Outperform Benchmark Pt for Alkaline Hydrogen Evolution.

Guaranteeing satisfactory catalytic behavior while ensuring high metal utilization has become the problem that needs to be addressed when designing noble-metal-based catalysts for electrochemical reactions. Here, well-dispersed ruthenium (Ru) based clusters with adjacent Ru single atoms (SAs) on layered sodium cobalt oxide (Ru/NC) are demonstrated as a superb electrocatalyst for alkaline HER. The Ru/NC catalyst demonstrates an activity increase by a factor of two relative to the commercial Pt/C. Operando characterizations in conjunction with density functional theory (DFT) simulations uncover the origin of the superior activity and establish a structure-performance relationship, that is, under HER condition, the real active species are Ru SAs and metallic Ru clusters supported on the NC substrate. The excellent alkaline HER activity of the Ru/NC catalyst can be understood by a spatially decoupled water dissociation and hydrogen desorption mechanism, where the NC substrate accelerates the water dissociation rate, and the generated H intermediates would then migrate to the Ru SAs or clusters and recombine to have H2 evolution. More importantly, comparing the two forms of Ru sites, it is the Ru cluster that dominates the HER activity.

Accelerated pyro-catalytic hydrogen production enabled by plasmonic local heating of Au on pyroelectric BaTiO3 nanoparticles.

The greatest challenge that limits the application of pyro-catalytic materials is the lack of highly frequent thermal cycling due to the enormous heat capacity of ambient environment, resulting in low pyro-catalytic efficiency. Here, we introduce localized plasmonic heat sources to rapidly yet efficiently heat up pyro-catalytic material itself without wasting energy to raise the surrounding temperature, triggering a significantly expedited pyro-catalytic reaction and enabling multiple pyro-catalytic cycling per unit time. In our work, plasmonic metal/pyro-catalyst composite is fabricated by in situ grown gold nanoparticles on three-dimensional structured coral-like BaTiO3 nanoparticles, which achieves a high hydrogen production rate of 133.1 ± 4.4 µmol·g-1·h-1 under pulsed laser irradiation. We also use theoretical analysis to study the effect of plasmonic local heating on pyro-catalysis. The synergy between plasmonic local heating and pyro-catalysis will bring new opportunities in pyro-catalysis for pollutant treatment, clean energy production, and biological applications.

Full quantum search for high Tc two-dimensional van der Waals ferromagnetic semiconductors.

Atomic thin two-dimensional (2D) ferromagnetic (FM) semiconductors with high Curie temperatures (Tc) are essential for future spintronic applications. However, reliable theoretical searching for 2D FM semiconductors is still hard due to the complexity of strong quantum fluctuations in 2D systems. We have proposed a full quantum search (FulQuanS) method to tackle the difficulty, and finally identified five 2D semiconductors of CrX3 (X = I, Br, Cl), CuCl3 and FeCl2 with FM order at finite temperature from the pool of 3721 potential 2D structures. Via the method of renormalized spin wave theory (SW) and quantum Monte Carlo simulations (QMC), we located the Tc for CrX3 (X = I, Br, Cl), CuCl3 and FeCl2 at 48 K, 31 K, 18 K, 74 K and 931 K respectively, which excellently agree with experiments for CrX3 and reveal the superior performances of the new predicted structures. Furthermore, our QMC results demonstrated that the systems with low-spin numbers and/or low anisotropies have much higher Tc than the estimations of classical models e.g., Monte Carlo simulations based on classical Heisenberg models. Our findings suggest excellent candidates for future room-temperature spintronics, and shed light on the quantum effects inherent in 2D magnetism.

Structural characterization and in vitro osteogenic activity of ABPB-4, a heteropolysaccharide from the rhizome of Achyranthes bidentata.

Achyranthes bidentata is a species of flowering plant that is mainly distributed in China. The A. bidentata rhizome is a famous traditional Chinese medicine that has been widely used to treat lumbago, arthritis, and bone hyperplasia. In this work, A. bidentata rhizome was isolated and purified to obtain a pectic polysaccharide (ABPB-4). Chemical and spectral analyses showed that ABPB-4 had a main chain of →4)-α-d-GalpA-(1→ and →2,4)-α-l-Rhap-(1→, and the branch chains included →4)-ß-d-Galp-(1→, →6)-ß-d-Galp-(1→, →3,6)-ß-d-Galp-(1→, →5)-α-l-Araf-(1→ and →3,5)-α-l-Araf-(1→, and it was terminated with α-l-Araf-(1→ and ß-d-Galp-(1→. At concentrations of 0.01, 0.02, and 0.04 µmol/L, ABPB-4 significantly promotes the proliferation, differentiation, and mineralization of MC3T3-E1 cells in vitro, and it appreciably enhances the mRNA expression levels of osteogenic-related genes in these cells. Overall, the results reported herein indicate that ABPB-4 has outstanding osteogenic activity, and that it may be used as an anti-osteoporosis agent in the future.

Physically Compatible Machine Learning Study on the Pt-Ni Nanoclusters.

Pt-Ni alloy nanoclusters are essential for high-performance catalysis, and the full description for the finite temperature properties is highly desired. Here we developed an efficient machine learning method to evaluate the accurate structure-stability correspondence in a Pt(85-x)-Nix nanocluster over the structural space with a dimension of 3.84 × 1025. On the basis of the physical model and big-data analysis, for the first time, we demonstrated that the segregation-extent bond order parameter (BOP) and the shell-resolved undercoordination ratio play the key roles in the structural stability. This a priori knowledge extremely reduced the computational costs and enhanced the accuracies. With the 500-sample train data set generated by density functional theory (DFT)-level geometry optimizations, we fit the machine-learning excess energy potential and verified the mean-square-error is <0.13. Our physically niche genetic-machine learning program (PNG-ML) searched 2.5 × 105 structures and predicted precisely the most stable Pt43-Ni42 (x = 42). The structural space dimension was reduced by 1020 fold using our PNG-ML method. The Pt/Ni ratio of the most stable nanocluster is 1.02, which is highly consistent with the experimental observation of 1.0. The above results provide reliable theoretical references for the realistic applications of Pt-Ni nanoclusters and suggest feature engineering for future studies on binary alloys nanostructures.

Superhydrophobic, photo-sterilize, and reusable mask based on graphene nanosheet-embedded carbon (GNEC) film.

The 2019 coronavirus disease (COVID-19) has affected more than 200 countries. Wearing masks can effectively cut off the virus spreading route since the coronavirus is mainly spreading by respiratory droplets. However, the common surgical masks cannot be reused, resulting in the increasing economic and resource consumption around the world. Herein, we report a superhydrophobic, photo-sterilize, and reusable mask based on graphene nanosheet-embedded carbon (GNEC) film, with high-density edges of standing structured graphene nanosheets. The GNEC mask exhibits an excellent hydrophobic ability (water contact angle: 157.9°) and an outstanding filtration efficiency with 100% bacterial filtration efficiency (BFE). In addition, the GNEC mask shows the prominent photo-sterilize performance, heating up to 110 °C quickly under the solar illumination. These high performances may facilitate the combat against the COVID-19 outbreaks, while the reusable masks help reducing the economic and resource consumption. Electronic Supplementary Material: Supplementary material (further details of electron cyclotron resonance (ECR) sputtering system, deposition of GNEC film, fabrication of GNEC mask, and characterization of the GNEC mask) is available in the online version of this article at 10.1007/s12274-020-3158-1.

A Symmetry-Breaking Phase in Two-Dimensional FeTe2 with Ferromagnetism above Room Temperature.

Recently, ferromagnetism observed in monolayer two-dimensional (2D) materials has attracted attention due to the promise of its application in next-generation spintronics. Here, we predict a symmetry-breaking phase in 2D FeTe2 that differs from conventional transition metal ditellurides shows superior stability and room-temperature ferromagnetism. Through density functional theory calculations, we find the exchange interactions in FeTe2 consist of short-range superexchange and long-range oscillatory exchanges mediated by itinerant electrons. For six nearest neighbors, the exchange constants are calculated to be 50.95, 33.41, 2.70, 11.02, 14.46, and -4.12 meV. Furthermore, the strong relativistic effects on Te2+ induce giant out-of-plane exchange anisotropy and open up a significantly large spin wave gap (ΔSW) of 1.22 meV. All of this leads to robust ferromagnetism with the Tc surpassing 423 K, which is predicted by the renormalization group Monte Carlo method, sufficiently higher than room temperature. Our findings shed light on the promising future of FeTe2 in 2D magnetic research and spintronic applications.

C-H oxidation enhancement on a gold nanoisland by atomic-undercoordination induced polarization.

C-H activation is of great significance in the chemical industry while an effective solvent-free catalyst is highly desired. This work shows that a gold nanoisland which was inert in the bulk is effective for C-H activation reactions. We investigated the C-H activation of toluene on an Au nanoisland (58 atoms) using relativistic density functional theory (DFT). We found that (i) the bonds between under-coordinated gold atoms (corner site) shrink spontaneously and become stronger; (ii) the valence charges of corner atoms are polarized to the upper edge of the valence band (near the Fermi level), indicating the electron donation ability in the catalytic process; (iii) during C-H oxidation, the indirect path (O2 dissociation and O-H bonding) and direct path (O2-H bonding) were considered. The Au-O2 complex is active enough to abstract a hydrogen atom directly from toluene, with a barrier that is 6.8 kcal mol-1 lower than that of the indirect path; and (iv) a transfer of up to ∼0.8 electrons from gold to O2 occurs. Moreover, hybridization between delocalized gold orbitals and oxygen p-orbitals leads to the stabilization of the singlet spin state of Au58O. Our results suggest that undercoordination-charge-polarization are key factors for the C-H oxidation catalyzed by an Au nanoisland.

Bias-Modulated High Photoelectric Response of Graphene-Nanocrystallite Embedded Carbon Film Coated on n-Silicon.

We propose that bias-modulated graphene-nanocrystallites (GNs) grown vertically can enhance the photoelectric property of carbon film coated on n-Si substrate. In this work, GN-embedded carbon (GNEC) films were deposited by the electron cyclotron resonance (ECR) sputtering technique. Under a reverse diode bias which lifts the Dirac point of GNs to a higher value, the GNEC film/n-Si device achieved a high photocurrent responsivity of 0.35 A/W. The bias-modulated position of the Dirac point resulted in a tunable ON/OFF ratio and a variable spectral response peak. Moreover, due to the standing structured GNs keeping the transport channels, a response time of 2.2 µs was achieved. This work sheds light on the bias-control wavelength-sensitive photodetector applications.