Topological Exact Flat Bands in Two-Dimensional Materials under Periodic Strain.

We study flat bands and their topology in 2D materials with quadratic band crossing points under periodic strain. In contrast to Dirac points in graphene, where strain acts as a vector potential, strain for quadratic band crossing points serves as a director potential with angular momentum ℓ=2. We prove that when the strengths of the strain fields hit certain "magic" values, exact flat bands with C=±1 emerge at charge neutrality point in the chiral limit, in strong analogy to magic angle twisted-bilayer graphene. These flat bands have ideal quantum geometry for the realization of fractional Chern insulators, and they are always fragile topological. The number of flat bands can be doubled for certain point group, and the interacting Hamiltonian is exactly solvable at integer fillings. We further demonstrate the stability of these flat bands against deviations from the chiral limit, and discuss possible realization in 2D materials.

Controllable Solid-Phase Fabrication of an Fe2O3/Fe5C2/Fe-N-C Electrocatalyst toward Optimizing the Oxygen Reduction Reaction in Zinc-Air Batteries.

Preparing advanced electrocatalysts via solid-phase reactions encounters the challenge of low controllability for multiconstituent hybridization and microstructure modulation. Herein, a hydrothermal-mimicking solid-phase system is established to fabricate novel Fe2O3/Fe5C2/Fe-N-C composites consisting of Fe2O3/Fe5C2 nanoparticles and Fe,N-doped carbon species with varying morphologies. The evolution mechanism featuring a competitive growth of different carbon sources in a closed hypoxic space is elucidated for a series of Fe2O3/Fe5C2/Fe-N-C composites. The size and dispersity of Fe2O3/Fe5C2 nanoparticles, the graphitization degree of the carbonaceous matrix, and their diverse hybridization states lead to disparate electrocatalytic behaviors for the oxygen reduction reaction (ORR). Among them, microspherical Fe2O3/Fe5C2/Fe-N-C-3 exhibits an optimal ORR performance and the as-assembled zinc-air battery shows all-round superiority to the Pt/C counterpart. This work presents a mild solid-phase fabrication technique for obtaining a variety of nanocomposites with effective control over composition hybridization and microstructural modulation, which is significantly important for the design and optimization of advanced electrocatalysts.

Recycling of photovoltaic silicon waste for high-performance porous silicon/silver/carbon/graphite anode.

The rapid development photovoltaic industry has generated a huge amount of waste ultra-fine silicon cutting powder. The management and value-added recovery of silicon cutting waste is highly important for both environmental remediation and economic efficiency. In this work, silicon waste was used as a cost-effective raw material for the preparation of silicon/graphite anode for lithium-ion batteries. First, porous Si embedded with Ag particles (pSi/Ag) was produced by silver-assisted chemical etching (Ag-ACE). Then, pSi/Ag was loaded on a micron-sized graphite matrix (pSi/Ag/G), and organic carbon (C) produced by the pyrolysis of polyvinylpyrrolidone (PVP) acted as a link to closely connect pSi/Ag and graphite to form the pSi/Ag/C/G composite. The incorporated Ag particles and the porous structure improve electron transfer and mitigate the volume expansion effect of silicon. The novel design and structure of the anode can maintain the integrity of the electrode during cycling, and thus strongly improve cycling stability. The prepared pSi/Ag/C/G composite exhibited a large initial discharge capacity of 2353 mAh/g at 0.5 A/g and good initial coulombic efficiency of 83%, delivering a high capacity of 972 mAh/g at 1 A/g after 200 cycles. This work confirmed the possibility of the preparation of lithium battery silicon-carbon anode from silicon waste and provides a promising new avenue for value-added utilization of silicon cutting waste materials.

PSi@SiOx/Nano-Ag composite derived from silicon cutting waste as high-performance anode material for Li-ion batteries.

Integration of photovoltaic (PV) power generation and energy storage has been widely believed to be the ultimate solution for future energy demands. Herein, an ingenious method was reported to make full use of photovoltaic silicon cutting waste (SiCW) natural characters fabricating PSi@SiOx/Nano-Ag composite as anode material for high-performance lithium-ion batteries. The sheet-like structure with nano/micropores and native SiOx layer addressed the volume expansion issues of Si material. Ag nanoparticles greatly enhanced electrical conductivity of composite and promoted Li+/e- transport. Synergistic effect of the designed PSi@SiOx/Nano-Ag composite contributed outstanding cyclic performance with reversible capacity of 1409mAhg-1 after 500 cycles. Notably, full LIBs with PSi@SiOx/Nano-Ag anode and commercial Li[Ni0.6Co0.2Mn0.2]O2 (NCM622) cathode delivered stable capacity of 137.5mAhg-1 at current density of 200 mA g-1, accompanying with a high energy density of 438 Wh kg-1. Furthermore, electrochemical Li+ storage behavior of this PSi@SiOx/Nano-Ag electrode was studied, and reaction mechanism and crystal structure evolution during cycles were also revealed by in-situ XRD analysis. The synthesis method is facile and cost-effective, which paves a novel way towards high-performance Si-based anodes and promising markets for both solar photovoltaic and lithium-ion battery industries.

Inflammatory cytokines derived from peripheral blood contribute to the modified electroconvulsive therapy-induced cognitive deficits in major depressive disorder.

Little is known about the pathophysiology of memory deficits in patients with major depressive disorder (MDD) treated with modified electroconvulsive therapy (MECT). This study examined the profiles of cytokines, the memory function, and their association in MECT-treated MDD patients. Forty first-episode, drug-free MDD patients and 40 healthy controls were recruited. MECT was started with antidepressant treatment at a stable initial dose. The Wechsler Memory Scale (WMS) and Hamilton Rating Scale for Depression 17 (HRSD-17) were used to assess the cognitive function. MDD patients were divided into the memory impairment group (WMS < 50) and the non-memory impairment group (WMS ≥ 50) based on the total WMS scores after MECT. The levels of NOD-like receptor 3 (NLRP3) inflammasome, interleukin-18 (IL-18) and nuclear factor kappa-B (NF-κB) in the serum were measured. MDD patients showed significantly higher levels of NLRP3 inflammasome, IL-18 and NF-κB than that in the controls prior to MECT, and the levels also significantly increased after MECT. In MDD patients, the serum levels of these inflammatory cytokines were negatively associated with the total WMS scores and likely contributed to the scores independently. The receiver operating characteristic curve showed that the serum levels of these inflammatory cytokines may predict the cognitive impairment risk in MDD patients receiving MECT. Abnormal levels of NLRP3 inflammasome, IL-18 and NF-κB reflecting the disturbed balance of pro-inflammatory and anti-inflammatory mechanisms likely contribute to the MECT-induced cognitive deficits in MDD patients.

Silicon recovery from diamond wire saw silicon powder waste with hydrochloric acid pretreatment: An investigation of Al dissolution behavior.

Silicon recovery from diamond wire saw silicon powder (DWSSP) waste is of great significance for increasing production profits and alleviating hazardous effects on the ecological environment. The purity of recovered silicon powder is determined by the purification efficiency during acid leaching pretreatment. Because the metallic impurities present in DWSSP are mostly physically mixed rather than chemically bound, the reaction rate is very fast in the initial stage of acid leaching, whereas it is difficult to dissolve the retained impurities in the later stage with the depletion of metal fragments adhered on the surface of the silicon matrix. Many prior studies have failed to consider the retained metallic impurities that reside in the inner silicon particle surfaces. Therefore, this study investigates the dissolution behavior of retained impurities via the dissolution of Al in HCl solution as an example. Thermodynamic results indicate that the Al dissolution process is dominated by entropic changes (ΔS0), rather than enthalpic changes (ΔH0). Furthermore, the dissolution behavior of Al is in accordance with the diffusion-controlled step in the Avrami mode, and the kinetic parameters were found to be A=5.85×107, Ea=49.27kJ·mol-1, and m<1. The determined dissolution behavior provides a clear understanding of the removal of retained metallic impurities from DWSSP via an acid leaching pretreatment. This study provides enlightenment for the further purification of silicon recovered from DWSSP waste.

High-Performance Porous Silicon/Nanosilver Anodes from Industrial Low-Grade Silicon for Lithium-Ion Batteries.

Silicon (Si) has been considered as one of the most promising candidates for the next-generation lithium-ion battery (LIB) anode materials owing to its huge theoretical specific capacity of 4200 mA h g-1. However, the practical application of Si anodes in commercial LIBs is facing challenges because of the lack of scalable and cost-effective methods to prepare Si-based anode materials with proper microstructure and competitive electrochemical performances. Herein, we report a facile and scalable method to produce multidimensional porous silicon embedded with a nanosilver particle (pSi/Ag) composite from commercially available low-cost metallurgical-grade silicon (MG-Si) powder. The unique hybrid structure contributes to fast electronic transport and relieves volume change of silicon during the charge-discharge process. The pSi/Ag composite exhibits a large initial discharge capacity (3095 mA h g-1 at a high current of 1 A g-1), an excellent cycling performance (1930 mA h g-1 at 1 A g-1 after 50 cycles), and outstanding rate capacities (up to 1778 mA h g-1 at a higher current of 2 A g-1). After the samples are modified by reduced graphene oxide, the capacities of the pSi/Ag@RGO composite electrode can still be maintained over 1000 mA h g-1 after 200 cycles. This study provides a simple and effective strategy for production of high-performance anode materials.

Facile in situ fabrication of biomorphic Co2P-Co3O4/rGO/C as an efficient electrocatalyst for the oxygen reduction reaction.

Streptococcus thermophilus, a Gram-positive (G+) bacterium featuring a teichoic acid-rich cell wall, has been employed as both a phosphorus source and template to synthesize a biomorphic Co2P-Co3O4/rGO/C composite as an efficient electrocatalyst for the oxygen reduction reaction (ORR). Different from the conventional method for the synthesis of phosphides, bio-derivative phosphorus vapor was emitted from the inside out, which facilitated the in situ transformation of the chemically adsorbed Co precursor on the bacteria into Co2P-Co3O4 heterogeneous nanoparticles, which featured a Co2P-rich body and Co3O4-rich surface. Besides, reduced graphene oxide (rGO) was also introduced in the synthetic process to keep Co2P-Co3O4 scattered and further promote the electron transport efficiency. All the Co2P-Co3O4 nanoparticles and rGO sheets were supported on the bacteria-derived carbon substrate with submicron-spherical morphology. The as-obtained Co2P-Co3O4/rGO/C composite exhibited excellent electrocatalytic performance for ORR with onset and half-wave potentials of 0.91 and 0.80 V vs. RHE, respectively. Furthermore, its long-term stability and methanol tolerance were better than those of commercial Pt/C. Thus, this work presents a new strategy of using an interior bio-phosphorus source to obtain heterojunction particles featuring a phosphide-rich body and oxide-rich surface, which may provide some insights for the construction of efficient heterogeneous electrocatalysts.