Stable Lithium Metal Batteries Enabled by Lithiophilic Core-Shell Nanowires on Copper Foam.

Lithium (Li) metal batteries have attracted considerable research attention due to their exceptionally high theoretical capacity. However, the commercialization of Li metal batteries faces challenges, primarily attributed to uncontrolled growth of Li dendrites, which raises safety concerns and lowers coulombic efficiency. To mitigate Li dendrites growth and attain dense Li deposition, the hybrid SiO2-Cu2O lithiophilic film applied to a 3D copper foam current collector is developed to regulate the interfacial properties for achieving even and dense Li deposition. The SiO2-Cu2O possesses strong Li+ trapping capability through strong lithiophilicity from Cu2O. Additionally, the SiO2-Cu2O enables uniform ion diffusion through the domain-limiting effect of the holes in the SiO2 layer, inducing an even and dense Li plating/stripping behavior at a large capacity. Furthermore, the SiO2 layer promotes the formation of an initial high inorganic content Solid Electrolyte Interphase (SEI) through selective preferential binding with anion and solvent molecules. When the SiO2-Cu2O@Li anode is coupled with a LiFePO4 (LFP) cathode, the resulting full cell exhibits superior cycling stability and rate performance. These results provide a facile approach to construct a lithiophilic current collector for practical Li metal anodes.

Construction of Selective Ion Transport Polymer at Anode-Electrolyte Interface for Stable Aqueous Zinc-Ion Batteries.

Rampant dendrite formation and serious adverse parasitic reactions induced by migration of dissolved V/Mn cathode ions on Zn anode have hampered the high performance of aqueous zinc-ion batteries (AZIBs). Inspired by the coordination chemistry between functional groups of polymer and electrolyte ions, a freestanding layer consisting of dopamine-functionalized polypyrrole (DA-PPy) nanowires served as a selective ion transport layer at the anode-electrolyte interface to address these two issues, which could simultaneously avoid polarization caused by the introduction of an additional interface. On the one hand, the DA-PPy layer displays excellent zinc ion and charge transfer ability, as well as provides chemical homochanneling for zinc ions at the interface, which endow the DA-PPy layer with properties as a chemical guider and physical barrier for dendrite inhibition. On the other hand, the DA-PPy layer can trap excess transition metal ions fleeing from the cathodes, thus serving as a chemical barrier, preventing the formation of Vx+/Mnx+-passivation on the surface of the zinc anode. Consequently, the AZIBs based on V2O5 and MnO2 cathodes involving the DA-PPy functional layer show a great improvement in the capacity retention.

Defective oxygen inert phase stabilized high-voltage nickel-rich cathode for high-energy lithium-ion batteries.

Pushing layered cathode to higher operating voltage can facilitate the realization of high-energy lithium-ion batteries. However, the released oxygen species initiate materials surface upon highly delithiated states will react severely with electrolyte, accelerating the structure deterioration and triggering the thermal degradation. Here we propose an inert phase of La2Mo2O9 with abundant oxygen vacancies (about 41%) by regulating the annealing temperature to engineer the cathode interface beyond conventional modifications. By employing LiNi0.8Co0.1Mn0.1O2 as a model system and extending to higher voltage-operated LiCoO2 and Li-rich cathode, we demonstrate that the introduced lanthanum and molybdenum ions will transfer electrons to enhance the surface oxygen electronegativities, thus served as "oxygen anchor" to alleviate oxygen evolution. Furthermore, the possible released oxygen can be operando captured and reserved by ß-phase La2Mo2O9 depositor for the intrinsic high oxygen vacancy formation energy. The reaction involving oxygen species with electrolyte is fundamentally diminished, thus effectively mitigate the structure deterioration and elevate the electrochemical performances, enabling a 1.5-Ah pouch-type full cell to exhibit negligible 6.0% capacity loss after 400 cycles.

Highly Reversible Zn Metal Anodes Enabled by Increased Nucleation Overpotential.

Dendrite formation severely compromises further development of zinc ion batteries. Increasing the nucleation overpotential plays a crucial role in achieving uniform deposition of metal ions. However, this strategy has not yet attracted enough attention from researchers to our knowledge. Here, we propose that thermodynamic nucleation overpotential of Zn deposition can be boosted through complexing agent and select sodium L-tartrate (Na-L) as example. Theoretical and experimental characterization reveals L-tartrate anion can partially replace H2O in the solvation sheath of Zn2+, increasing de-solvation energy. Concurrently, the Na+ could absorb on the surface of Zn anode preferentially to inhibit the deposition of Zn2+ aggregation. In consequence, the overpotential of Zn deposition could increase from 32.2 to 45.1 mV with the help of Na-L. The Zn-Zn cell could achieve a Zn utilization rate of 80% at areal capacity of 20 mAh cm-2. Zn-LiMn2O4 full cell with Na-L additive delivers improved stability than that with blank electrolyte. This study also provides insight into the regulation of nucleation overpotential to achieve homogeneous Zn deposition.

Engineering a Copper Single-Atom Electron Bridge to Achieve Efficient Photocatalytic CO2 Conversion.

Developing highly efficient and stable photocatalysts for the CO2 reduction reaction (CO2 RR) remains a great challenge. We designed a Z-Scheme photocatalyst with N-Cu1 -S single-atom electron bridge (denoted as Cu-SAEB), which was used to mediate the CO2 RR. The production of CO and O2 over Cu-SAEB is as high as 236.0 and 120.1 µmol g-1 h-1 in the absence of sacrificial agents, respectively, outperforming most previously reported photocatalysts. Notably, the as-designed Cu-SAEB is highly stable throughout 30 reaction cycles, totaling 300 h, owing to the strengthened contact interface of Cu-SAEB, and mediated by the N-Cu1 -S atomic structure. Experimental and theoretical calculations indicated that the SAEB greatly promoted the Z-scheme interfacial charge-transport process, thus leading to great enhancement of the photocatalytic CO2 RR of Cu-SAEB. This work represents a promising platform for the development of highly efficient and stable photocatalysts that have potential in CO2 conversion applications.

Highly Heterogeneous Polarization and Solvation of Gold Nanoparticles in Aqueous Electrolytes.

The performance of gold nanoparticles (NPs) in applications depends critically on the structure of the NP-solvent interface, at which the electrostatic surface polarization is one of the key characteristics that affects hydration, ionic adsorption, and electrochemical reactions. Here, we demonstrate significant effects of explicit metal polarizability on the solvation and electrostatic properties of bare gold NPs in aqueous electrolyte solutions of sodium salts of various anions (Cl-, BF4-, PF6-, nitrophenolate, and 3- and 4-valent hexacyanoferrate), using classical molecular dynamics simulations with a polarizable core-shell model for the gold atoms. We find considerable spatial heterogeneity of the polarization and electrostatic potentials on the NP surface, mediated by a highly facet-dependent structuring of the interfacial water molecules. Moreover, ion-specific, facet-dependent ion adsorption leads to considerable alterations of the interfacial polarization. Compared to nonpolarizable NPs, surface polarization modifies water local dipole densities only slightly but has substantial effects on the electrostatic surface potentials and leads to significant lateral redistributions of ions on the NP surface. Besides, interfacial polarization effects cancel out in the far field for monovalent ions but not for polyvalent ions, as anticipated from continuum "image-charge" concepts. Far-field effective Debye-Hückel surface potentials change accordingly in a valence-specific fashion. Hence, the explicit charge response of metal NPs is crucial for the accurate description and interpretation of interfacial electrostatics (e.g., for charge transfer and interfacial polarization in catalysis and electrochemistry).

Ion-Specific Adsorption on Bare Gold (Au) Nanoparticles in Aqueous Solutions: Double-Layer Structure and Surface Potentials.

We study the solvation and electrostatic properties of bare gold (Au) nanoparticles (NPs) of 1-2 nm in size in aqueous electrolyte solutions of sodium salts of various anions with large physicochemical diversity (Cl-, BF4-, PF6-, Nip- (nitrophenolate), 3- and 4-valent hexacyanoferrate (HCF)) using nonpolarizable, classical molecular dynamics computer simulations. We find a substantial facet selectivity in the adsorption structure and spatial distribution of the ions at the AuNPs: while sodium and some of the anions (e.g., Cl-, HCF3-) adsorb more at the "edgy" (100) and (110) facets of the NPs, where the water hydration structure is more disordered, other ions (e.g., BF4-, PF6-, Nip-) prefer to adsorb strongly on the extended and rather flat (111) facets. In particular, Nip-, which features an aromatic ring in its chemical structure, adsorbs strongly and perturbs the first water monolayer structure on the NP (111) facets substantially. Moreover, we calculate adsorptions, radially resolved electrostatic potentials as well as the far-field effective electrostatic surface charges and potentials by mapping the long-range decay of the calculated electrostatic potential distribution onto the standard Debye-Hückel form. We show how the extrapolation of these values to other ionic strengths can be performed by an analytical Adsorption-Grahame relation between the effective surface charge and potential. We find for all salts negative effective surface potentials in the range from -10 mV for NaCl down to about -80 mV for NaNip, consistent with typical experimental ranges for the zeta potential. We discuss how these values depend on the surface definition and compare them to the explicitly calculated electrostatic potentials near the NP surface, which are highly oscillatory in the ±0.5 V range.

Competitive Salt Precipitation/Dissolution During Free-Water Reduction in Water-in-Salt Electrolyte.

Water-in-salt electrolytes based on highly concentrated bis(trifluoromethyl)sulfonimide (TFSI) promise aqueous electrolytes with stabilities nearing 3 V. However, especially with an electrode approaching the cathodic (reductive) stability, cycling stability is insufficient. While stability critically relies on a solid electrolyte interphase (SEI), the mechanism behind the cathodic stability limit remains unclear. Now, two distinct reduction potentials are revealed for the chemical environments of free and bound water and that both contribute to SEI formation. Free water is reduced about 1 V above bound water in a hydrogen evolution reaction (HER) and is responsible for SEI formation via reactive intermediates of the HER; concurrent LiTFSI precipitation/dissolution establishes a dynamic interface. The free-water population emerges, therefore, as the handle to extend the cathodic limit of aqueous electrolytes and the battery cycling stability.

[Optical Absorption Properties of Brown Carbon Aerosols in Guangzhou].

In this work, we conducted measurements using a seven-wavelength aethalometer, an online OCEC analyzer, and a MARGA to investigate brown carbon (BrC) absorption properties and source origins during the winter of 2014 at Panyu station, Guangzhou. The results showed that the average absorption contributions of BrC decreased with an increase in wavelength, measured as 25.9%, 19.7%, 14.1%, 11.6%, and 7.7% at 370 nm, 470 nm, 520 nm, 590 nm, and 660 nm, respectively. Diurnal variations in BrC absorption and the concentrations of potassium cations (K+) and organic carbon (OC) was high at night and low during the day, which was attributed to biomass burning. This indicated that BrC was emitted from straw burning in rural areas and accumulated in the steady planetary boundary layer at night. Diurnal variations in the ratio of BrC absorption to OC concentrations showed a distinct dip during the afternoon, indicating that aged aerosol and secondary organic aerosol (SOA) had a weaker BrC absorption capacity. There was a good overall correlation between BrC absorption and K+ concentrations. BrC absorption was also moderately related to the concentrations of ammonium cations (NH4+) and nitrate anions (NO3-).

A new species of the genus Oxyporus Fabricius (Coleoptera: Staphylinidae: Oxyporinae) in Yunnan Province, China.

A new species of the genus Oxyporus Fabricius, 1775 is described based on specimens collected in Yunnan Province, China, namely Oxyporus (Oxyporus) tuantianius sp. nov. from Xinping County. The number of Oxyporus species worldwide is thus increased to 131. Color images of the habitus and aedeagus of the new species are included. A key to the Oxyporus species of Yunnan Province is provided.

Confinement Effects on an Electron Transfer Reaction in Nanoporous Carbon Electrodes.

Nanoconfinement generally leads to a drastic effect on the physical and chemical properties of ionic liquids. Here we investigate how the electrochemical reactivity in such media may be impacted inside of nanoporous carbon electrodes. To this end, we study a simple electron transfer reaction using molecular dynamics simulations. The electrodes are held at constant electric potential by allowing the atomic charges on the carbon atoms to fluctuate. We show that the Fe3+/Fe2+ couple dissolved in an ionic liquid exhibits a deviation with respect to Marcus theory. This behavior is rationalized by the stabilization of a solvation state of the Fe3+ cation in the disordered nanoporous electrode that is not observed in the bulk. The simulation results are fitted with a recently proposed two solvation state model, which allows us to estimate the effect of such a deviation on the kinetics of electron transfer inside of nanoporous electrodes.

On Structural Features Necessary for Near-IR-Light Photocatalysts.

In the search for photocatalysts that can directly utilize near-IR (NIR) light, we investigated three oxides Cu3(OH)4SO4 (antlerite), Cu4(OH)6SO4, and Cu2(OH)3Cl by photodecomposing 2,4-dichlorophenol over them under NIR irradiation and by comparing their electronic structures with that of the known NIR photocatalyst Cu2(OH)PO4. Both Cu3(OH)4SO4 and Cu4(OH)6SO4 are NIR photocatalysts, but Cu2(OH)3Cl is not. Thus, in addition to the presence of two different CuOm and Cu'On polyhedra linked with Cu-O-Cu' bridges, the presence of acceptor groups (e.g., SO4, PO4) linked to the metal oxygen polyhedra is necessary for NIR photocatalysts.

The synergistic effect between effective mass and built-in electric field for the transfer of carriers in nonlinear optical materials.

Recent experiments have demonstrated that the typical nonlinear optical material K3B6O10Br can be an excellent photocatalyst under ultraviolet (UV) light irradiation. To understand the origin of the photocatalytic activity and further improve its photocatalytic efficiency to develop alternative photocatalysts, the built-in electric field and the electron effective mass and their synergistic effect on transfer and the separation of carriers in K3B6O10X (X = Br, Cl) were investigated by means of first-principles calculations. Our results show that the built-in electric field and the smallest effective mass of holes in K3B6O10Br are both along the [001] direction. In contrast, the effective masses of electrons are isotropic because of the spherically symmetric s orbitals at the conduction band minimum (CBM). Therefore, the electric field can promote efficient transfer and separation of the photogenerated carriers along the [001] direction. As a consequence, the synergistic effect of built-in electric field and the isotropy of the electron effective mass results in the {001} surface, to which most of the carriers will accumulate, showing the highest photocatalytic activity. Similar results can also be obtained for a K3B6O10Cl crystal considering the analogous structure with that of K3B6O10Br. The present study may provide theoretical insight to develop the photocatalytic performance of nonlinear optical materials.

Synthesis and characterization of ZnS with controlled amount of S vacancies for photocatalytic H2 production under visible light.

Controlling amount of intrinsic S vacancies was achieved in ZnS spheres which were synthesized by a hydrothermal method using Zn and S powders in concentrated NaOH solution with NaBH4 added as reducing agent. These S vacancies efficiently extend absorption spectra of ZnS to visible region. Their photocatalytic activities for H2 production under visible light were evaluated by gas chromatograph, and the midgap states of ZnS introduced by S vacancies were examined by density functional calculations. Our study reveals that the concentration of S vacancies in the ZnS samples can be controlled by varying the amount of the reducing agent NaBH4 in the synthesis, and the prepared ZnS samples exhibit photocatalytic activity for H2 production under visible-light irradiation without loading noble metal. This photocatalytic activity of ZnS increases steadily with increasing the concentration of S vacancies until the latter reaches an optimum value. Our density functional calculations show that S vacancies generate midgap defect states in ZnS, which lead to visible-light absorption and responded.

GeH: a novel material as a visible-light driven photocatalyst for hydrogen evolution.

A novel 2D material germanane (GeH), which was synthesized by an ion-exchange approach, was firstly found to exhibit photocatalytic performance in the hydrogen evolution of water splitting and decomposition of organic contaminants under illumination of visible light (λ ≥ 420 nm).

Tuning photocatalytic performance of the near-infrared-driven photocatalyst Cu2(OH)PO4 based on effective mass and dipole moment.

Recently, Cu2(OH)PO4 was found as the first photocatalyst active in the near-infrared(NIR) region of the solar spectrum (Angew. Chem., Int. Ed., 2013, 52, 4810; Chem. Eng. News, 2013, 91, 36), motivating us to explore systemically its photocatalytic mechanism under near-infrared light and how to improve and tune its photocatalytic performance. Herein, electronic structures, and effective masses of electron and hole at energy band edges are theoretically investigated by employing spin-polarized density functional theory calculations. The calculated energy band structure supports the absorption spectra of Cu2(OH)PO4 in the NIR region corresponding to the electron excitation from the valence band to the unoccupied bands in the gap. Our charge density analysis indicates that the O atoms in the hydroxyl serves as the effective bridge for the favoring separation of the photogenerated electron-hole pairs. Furthermore, the effective masses of electron and hole analysis demonstrate that the separation and transfer of photogenerated carriers along the [011] direction may be more effective than other possible directions. A qualitative comparison of carrier transfer ability along all the directions in the specific planes is displayed by the three-dimensional band structure. Interestingly, the calculated net dipole moment for the two basic units of Cu2(OH)PO4, octahedron and trigonal bipyramid, indicate that the macroscopic dipole moment for Cu2(OH)PO4 is zero, however, the distorted octahedron unit has a net dipole moment, which enables us to tune the macroscopic dipole moment by doping. The present work provides theoretical insight leading to a better understanding of the photocatalytic performance of Cu2(OH)PO4 and it may be beneficial to prepare more efficient Cu2(OH)PO4 for NIR light photocatalysis, which will also be helpful to design and prepare novel photocatalysts.

First-principles study of one-dimensional sandwich wires [(P)5TM]∞ (TM = Ti, V, Cr, Mn, Fe, Co).

Since the discovery of ferrocene, many one-dimensional metallic sandwich molecular wires have been identified. However, most of the known systems are assembled from organic molecules. Suffering from many drawbacks has, however, hampered their widespread applications. With the goal of breaking this logjam, we provide a blueprint for the designing of a variety of novel sandwich molecular wires ([(P)5TM]∞, TM = Ti, V, Cr, Mn, Fe, and Co) assembled from ferrocene-like inorganic molecules (P)5TM, offering evidence of the existence of inorganic molecular wires in this class. We present first-principles calculations to investigate systematically the electronic and magnetic properties of such novel inorganic sandwich molecular wires. Compared with the organic molecular wires, all the inorganic [(P)5TM]∞ wires are of large magnetic moment. Among them, we find that [(P)5V]∞, [(P)5Cr]∞ and [(P)5Mn]∞ display ferromagnetic character, while for [(P)5Ti]∞, [(P)5Fe]∞ and [(P)5Co]∞, the magnetic coupling is antiferromagnetic. More remarkably, the TM atoms distributed in these wires show regular docking and lead to structures with ordered spin signals, which is a long-term dream of spintronics. We propose that the difference in magnetic coupling for the studied systems is related to the competition between two exchange interactions of TM atoms. Specifically, we propound that the general mechanism for the formation of stable 1D [(P)5TM]∞ involves the transfer of one electron from the TM atom to the P5 ligand forming [Formula: see text] and TM(+) alternating structure.