Dualistic insulator states in 1T-TaS2 crystals.

While the monolayer sheet is well-established as a Mott-insulator with a finite energy gap, the insulating nature of bulk 1T-TaS2 crystals remains ambiguous due to their varying dimensionalities and alterable interlayer coupling. In this study, we present a unique approach to unlock the intertwined two-dimensional Mott-insulator and three-dimensional band-insulator states in bulk 1T-TaS2 crystals by structuring a laddering stack along the out-of-plane direction. Through modulating the interlayer coupling, the insulating nature can be switched between band-insulator and Mott-insulator mechanisms. Our findings demonstrate the duality of insulating nature in 1T-TaS2 crystals. By manipulating the translational degree of freedom in layered crystals, our discovery presents a promising strategy for exploring fascinating physics, independent of their dimensionality, thereby offering a "three-dimensional" control for the era of slidetronics.

A LaCl3-based lithium superionic conductor compatible with lithium metal.

Inorganic superionic conductors possess high ionic conductivity and excellent thermal stability but their poor interfacial compatibility with lithium metal electrodes precludes application in all-solid-state lithium metal batteries1,2. Here we report a LaCl3-based lithium superionic conductor possessing excellent interfacial compatibility with lithium metal electrodes. In contrast to a Li3MCl6 (M = Y, In, Sc and Ho) electrolyte lattice3-6, the UCl3-type LaCl3 lattice has large, one-dimensional channels for rapid Li+ conduction, interconnected by La vacancies via Ta doping and resulting in a three-dimensional Li+ migration network. The optimized Li0.388Ta0.238La0.475Cl3 electrolyte exhibits Li+ conductivity of 3.02 mS cm-1 at 30 °C and a low activation energy of 0.197 eV. It also generates a gradient interfacial passivation layer to stabilize the Li metal electrode for long-term cycling of a Li-Li symmetric cell (1 mAh cm-2) for more than 5,000 h. When directly coupled with an uncoated LiNi0.5Co0.2Mn0.3O2 cathode and bare Li metal anode, the Li0.388Ta0.238La0.475Cl3 electrolyte enables a solid battery to run for more than 100 cycles with a cutoff voltage of 4.35 V and areal capacity of more than 1 mAh cm-2. We also demonstrate rapid Li+ conduction in lanthanide metal chlorides (LnCl3; Ln = La, Ce, Nd, Sm and Gd), suggesting that the LnCl3 solid electrolyte system could provide further developments in conductivity and utility.

Sustainable methane utilization technology via photocatalytic halogenation with alkali halides.

Methyl halides are versatile platform molecules, which have been widely adopted as precursors for producing value-added chemicals and fuels. Despite their high importance, the green and economical synthesis of the methyl halides remains challenging. Here we demonstrate sustainable and efficient photocatalytic methane halogenation for methyl halide production over copper-doped titania using alkali halides as a widely available and noncorrosive halogenation agent. This approach affords a methyl halide production rate of up to 0.61 mmol h-1 m-2 for chloromethane or 1.08 mmol h-1 m-2 for bromomethane with a stability of 28 h, which are further proven transformable to methanol and pharmaceutical intermediates. Furthermore, we demonstrate that such a reaction can also operate solely using seawater and methane as resources, showing its high practicability as general technology for offshore methane exploitation. This work opens an avenue for the sustainable utilization of methane from various resources and toward designated applications.

Near-infrared-featured broadband CO2 reduction with water to hydrocarbons by surface plasmon.

Imitating the natural photosynthesis to synthesize hydrocarbon fuels represents a viable strategy for solar-to-chemical energy conversion, where utilizing low-energy photons, especially near-infrared photons, has been the ultimate yet challenging aim to further improving conversion efficiency. Plasmonic metals have proven their ability in absorbing low-energy photons, however, it remains an obstacle in effectively coupling this energy into reactant molecules. Here we report the broadband plasmon-induced CO2 reduction reaction with water, which achieves a CH4 production rate of 0.55 mmol g-1 h-1 with 100% selectivity to hydrocarbon products under 400 mW cm-2 full-spectrum light illumination and an apparent quantum efficiency of 0.38% at 800 nm illumination. We find that the enhanced local electric field plays an irreplaceable role in efficient multiphoton absorption and selective energy transfer for such an excellent light-driven catalytic performance. This work paves the way to the technique for low-energy photon utilization.

Suppressing the Dynamic Oxygen Evolution of Sodium Layered Cathodes through Synergistic Surface Dielectric Polarization and Bulk Site-Selective Co-Doping.

Utilizing anionic redox activity within layered oxide cathode materials represents a transformational avenue for enabling high-energy-density rechargeable batteries. However, the anionic oxygen redox reaction is often accompanied with irreversible dynamic oxygen evolution, leading to unfavorable structural distortion and thus severe voltage decay and rapid capacity fading. Herein, it is proposed and validated that the dynamic oxygen evolution can be effectively suppressed through the synergistic surface CaTiO3 dielectric coating and bulk site-selective Ca/Ti co-doping for layered Na2/3 Ni1/3 Mn2/3 O2 . The surface dielectric coating layer not only suppresses the surface oxygen release but more importantly inhibits the bulk oxygen migration by creating a reverse electric field through dielectric polarization. Meanwhile, the site-selective doping of oxygen-affinity Ca into Na layers and Ti into transition metal layers effectively stabilizes the bulk oxygen through modulating the O 2p band center and the oxygen migration barrier. Such a strategy also leads to a reversible structural evolution with a low volume change because of the enhanced structural integrality and improved oxygen rigidity. Because of these synergistic advantages, the designed electrode exhibits greatly suppressed voltage decay and capacity fading upon long-term cycling. This study affords a promising strategy for regulating the dynamic oxygen evolution to achieve high-capacity layered cathode materials.

Black Phosphorous Mediates Surface Charge Redistribution of CoSe2 for Electrochemical H2 O2 Production in Acidic Electrolytes.

Electrochemical generation of hydrogen peroxide (H2 O2 ) by two-electron oxygen reduction offers a green method to mitigate the current dependence on the energy-intensive anthraquinone process, promising its on-site applications. Unfortunately, in alkaline environments, H2 O2 is not stable and undergoes rapid decomposition. Making H2 O2 in acidic electrolytes can prevent its decomposition, but choices of active, stable, and selective electrocatalysts are significantly limited. Here, the selective and efficient two-electron reduction of oxygen toward H2 O2 in acid by a composite catalyst that is composed of black phosphorus (BP) nailed chemically on the metallic cobalt diselenide (CoSe2 ) surface is reported. It is found that this catalyst exhibits a 91% Faradic efficiency for H2 O2 product at an overpotential of 300 mV. Moreover, it can mediate oxygen to H2 O2 with a high production rate of ≈1530 mg L-1 h-1 cm-2 in a flow-cell reactor. Spectroscopic and computational studies together uncover a BP-induced surface charge redistribution in CoSe2 , which leads to a favorable surface electronic structure that weakens the HOO* adsorption, thus enhancing the kinetics toward H2 O2 formation.

Superior Fast-Charging Lithium-Ion Batteries Enabled by the High-Speed Solid-State Lithium Transport of an Intermetallic Cu6 Sn5 Network.

Superior fast charging is a desirable capability of lithium-ion batteries, which can make electric vehicles a strong competition to traditional fuel vehicles. However, the slow transport of solvated lithium ions in liquid electrolytes is a limiting factor. Here, a Lix Cu6 Sn5 intermetallic network is reported to address this issue. Based on electrochemical analysis and X-ray photoelectron spectroscopy mapping, it is demonstrated that the reported intermetallic network can form a high-speed solid-state lithium transport matrix throughout the electrode, which largely reduces the lithium-ion-concentration polarization effect in the graphite anode. Employing this design, superior fast-charging graphite/lithium cobalt oxide full cells are fabricated and tested under strict electrode conditions. At the charging rate of 6 C, the fabricated full cells show a capacity of 145 mAh g-1 with an extraordinary capacity retention of 96.6%. In addition, the full cell also exhibits good electrochemical stability at a high charging rate of 2 C over 100 cycles (96.0% of capacity retention) in comparison to traditional graphite-anode-based cells (86.1% of capacity retention). This work presents a new strategy for fast-charging lithium-ion batteries on the basis of high-speed solid-state lithium transport in intermetallic alloy hosts.

Interface engineering of Ta3N5 thin film photoanode for highly efficient photoelectrochemical water splitting.

Interface engineering is a proven strategy to improve the efficiency of thin film semiconductor based solar energy conversion devices. Ta3N5 thin film photoanode is a promising candidate for photoelectrochemical (PEC) water splitting. Yet, a concerted effort to engineer both the bottom and top interfaces of Ta3N5 thin film photoanode is still lacking. Here, we employ n-type In:GaN and p-type Mg:GaN to modify the bottom and top interfaces of Ta3N5 thin film photoanode, respectively. The obtained In:GaN/Ta3N5/Mg:GaN heterojunction photoanode shows enhanced bulk carrier separation capability and better injection efficiency at photoanode/electrolyte interface, which lead to a record-high applied bias photon-to-current efficiency of 3.46% for Ta3N5-based photoanode. Furthermore, the roles of the In:GaN and Mg:GaN layers are distinguished through mechanistic studies. While the In:GaN layer contributes mainly to the enhanced bulk charge separation efficiency, the Mg:GaN layer improves the surface charge inject efficiency. This work demonstrates the crucial role of proper interface engineering for thin film-based photoanode in achieving efficient PEC water splitting.

Self-Assembled Donor-Acceptor Dyad Molecules Stabilize the Heterojunction of Inverted Perovskite Solar Cells and Modules.

The heterointerface between a semiconducting metal oxide and a perovskite critically impacts on the overall performance of perovskite solar cells (PVSCs). Herein, we report a feasible yet effective strategy to suppress the interfacial reaction between nickel oxide and the perovskite via chemical passivation with self-assembled dyad molecules, which leads to the simultaneous improvement of the power conversion efficiencies (PCEs) and operational lifetimes of inverted PVSCs. As a result, inverted PVSCs consisting of simple methylammonium iodide perovskites have achieved an excellent PCE of 20.94% and decent photostability with 93% of the initial value after 600 h of 1 sun equivalent illumination. Moreover, this strategy can be readily translated into slot-die fabrication of perovskite modules, achieving a high PCE of 14.90% with an area of 19.16 cm2 (no shade in the interconnecting area) and a geometrical fill factor of 93%. Overall, this work provides an effective strategy to stabilize the vulnerable heterointerface in PVSCs.

Sulfur-anchoring synthesis of platinum intermetallic nanoparticle catalysts for fuel cells.

Atomically ordered intermetallic nanoparticles are promising for catalytic applications but are difficult to produce because the high-temperature annealing required for atom ordering inevitably accelerates metal sintering that leads to larger crystallites. We prepared platinum intermetallics with an average particle size of <5 nanometers on porous sulfur-doped carbon supports, on which the strong interaction between platinum and sulfur suppresses metal sintering up to 1000°C. We synthesized intermetallic libraries of small nanoparticles consisting of 46 combinations of platinum with 16 other metal elements and used them to study the dependence of electrocatalytic oxygen-reduction reaction activity on alloy composition and platinum skin strain. The intermetallic libraries are highly mass efficient in proton-exchange-membrane fuel cells and could achieve high activities of 1.3 to 1.8 amperes per milligram of platinum at 0.9 volts.

Boosting photoelectrochemical efficiency by near-infrared-active lattice-matched morphological heterojunctions.

Photoelectrochemical catalysis is an attractive way to provide direct hydrogen production from solar energy. However, solar conversion efficiencies are hindered by the fact that light harvesting has so far been of limited efficiency in the near-infrared region as compared to that in the visible and ultraviolet regions. Here we introduce near-infrared-active photoanodes that feature lattice-matched morphological hetero-nanostructures, a strategy that improves energy conversion efficiency by increasing light-harvesting spectral range and charge separation efficiency simultaneously. Specifically, we demonstrate a near-infrared-active morphological heterojunction comprised of BiSeTe ternary alloy nanotubes and ultrathin nanosheets. The heterojunction's hierarchical nanostructure separates charges at the lattice-matched interface of the two morphological components, preventing further carrier recombination. As a result, the photoanodes achieve an incident photon-to-current conversion efficiency of 36% at 800 nm in an electrolyte solution containing hole scavengers without a co-catalyst.

Efficient Photoelectrochemical Conversion of Methane into Ethylene Glycol by WO3 Nanobar Arrays.

Photoelectrochemical (PEC) conversion of methane (CH4 ) has been extensively explored for the production of value-added chemicals, yet remains a great challenge in high selectivity toward C2+ products. Herein, we report the optimization of the reactivity of hydroxyl radicals (. OH) on WO3 via facet tuning to achieve efficient ethylene glycol production from PEC CH4 conversion. A combination of materials simulation and radicals trapping test provides insight into the reactivity of . OH on different facets of WO3 , showing the highest reactivity of surface-bound . OH on {010} facets. As such, the WO3 with the highest {010} facet ratio exhibits a superior PEC CH4 conversion efficiency, reaching an ethylene glycol production rate of 0.47 µmol cm-2 h-1 . Based on in situ characterization, the methanol, which could be attacked by reactive . OH to form hydroxymethyl radicals, is confirmed to be the main intermediate for the production of ethylene glycol. Our finding is expected to provide new insight for the design of active and selective catalysts toward PEC CH4 conversion.

Aqueous solution processed MoS3 as an eco-friendly hole-transport layer for all-inorganic Sb2Se3 solar cells.

Here we report a solution processed environmentally friendly MoS3 hole-transport material for Sb2Se3 solar cells, where MoS3 exhibits a matched energy level relative to Sb2Se3. In the synthesis, H2S produced by the thermal decomposition of (NH4)2MoS4 is found to efficiently eliminate the antimony oxide impurity formed on the Sb2Se3 surface. Finally, the all-inorganic Sb2Se3 solar cell delivers an efficiency of 6.86% with excellent stability.

Probing the trap states in N-i-P Sb2(S,Se)3 solar cells by deep-level transient spectroscopy.

In this study, we provide fundamental understanding on defect properties of the Sb2(S,Se)3 absorber film and the impact on transmission of photo-excited carriers in N-i-P architecture solar cells by both deep level transient spectroscopy (DLTS) and optical deep level transient spectroscopy (ODLTS) characterizations. Through conductance-voltage and temperature-dependent current-voltage characterization under a dark condition, we find that the Sb2(S,Se)3 solar cell demonstrates good rectification and high temperature tolerance. The DLTS results indicates that there are two types of deep level hole traps H1 and H2 with active energy of 0.52 eV and 0.76 eV in the Sb2(S,Se)3 film, and this defect property is further verified by ODLTS. The two traps hinder the transmission of minority carrier (hole) and pinning the Fermi level, which plays a negative role in the improvement of open-circuit voltage for Sb2(S,Se)3 solar cells. This research suggests a critical direction toward the efficiency improvement of Sb2(S,Se)3 solar cells.

Metal chloride perovskite thin film based interfacial layer for shielding lithium metal from liquid electrolyte.

Fabricating a robust interfacial layer on the lithium metal anode to isolate it from liquid electrolyte is vital to restrain the rapid degradation of a lithium metal battery. Here, we report that the solution-processed metal chloride perovskite thin film can be coated onto the lithium metal surface as a robust interfacial layer to shield the lithium metal from liquid electrolyte. Via phase analysis and density functional theory calculations, we demonstrate that the perovskite layer can allow fast lithium ion shuttle under a low energy barrier of 0.45 eV without the collapse of framework. Such perovskite modification can realize stable cycling of LiCoO2|Li cells with an areal capacity of 2.8 mAh cm-2 using thin lithium metal foil (50 µm) and limited electrolyte (20 µl mAh-1) for over 100 cycles at 0.5 C. The metal chloride perovskite protection strategy could open a promising avenue for advanced lithium metal batteries.

Hermetically encapsulating sulfur by FePS3 flakes for high-performance lithium sulfur batteries.

Herein, hollow sulfur spheres encapsulated hermetically by FePS3 flakes (HSS@FePS3) are utilized in lithium sulfur batteries (LSBs). Via the encapsulation, soluble polysulfide can be trapped obviously and volume expansion during discharge can be accommodated effectively. The HSS@FePS3 cathode shows an excellent cycling stability even at a current density of 1C (a capacity decay of 0.0461% per cycle during 1000 cycles).

A Black Phosphorus-Graphite Composite Anode for Li-/Na-/K-Ion Batteries.

Black phosphorus (BP) is a desirable anode material for alkali metal ion storage owing to its high electronic/ionic conductivity and theoretical capacity. In-depth understanding of the redox reactions between BP and the alkali metal ions is key to reveal the potential and limitations of BP, and thus to guide the design of BP-based composites for high-performance alkali metal ion batteries. Comparative studies of the electrochemical reactions of Li+ , Na+ , and K+ with BP were performed. Ex situ X-ray absorption near-edge spectroscopy combined with theoretical calculation reveal the lowest utilization of BP for K+ storage than for Na+ and Li+ , which is ascribed to the highest formation energy and the lowest ion diffusion coefficient of the final potassiation product K3 P, compared with Li3 P and Na3 P. As a result, restricting the formation of K3 P by limiting the discharge voltage achieves a gravimetric capacity of 1300 mAh g-1 which retains at 600 mAh g-1 after 50 cycles at 0.25 A g-1 .

Natural Nanofibrous Cellulose-Derived Solid Acid Catalysts.

Solid acid catalysts (SACs) have attracted continuous research interest in past years as they play a pivotal role in establishing environmentally friendly and sustainable catalytic processes for various chemical industries. Development of low-cost and efficient SACs applicable to different catalysis processes are of immense significance but still very challenging so far. Here, we report a new kind of SACs consisting of sulfonated carbon nanofibers that are prepared via incomplete carbonization of low-cost natural nanofibrous cellulose followed by sulphonation with sulfuric acid. The prepared SACs feature nanofibrous network structures, high specific surface area, and abundant sulfonate as well as hydroxyl and carboxyl groups. Remarkably, the nanofibrous SACs exhibit superior performance to the state-of-the-art SACs for a wide range of acid-catalyzed reactions, including dimerization of α-methylstyrene, esterification of oleic acid, and pinacol rearrangement. The present approach holds great promise for developing new families of economic but efficient SACs based on natural precursors via scalable and sustainable protocols in the future.

On-surface synthesis and characterization of individual polyacetylene chains.

Polyacetylene (PA) comprises one-dimensional chains of sp2-hybridized carbon atoms that may take a cis or trans configuration. Owing to its simple chemical structure and exceptional electronic properties, PA is an ideal system to understand the nature of charge transport in conducting polymers. Here, we report the on-surface synthesis of both cis- and trans-PA chains and their atomic-scale characterization. The structure of individual PA chains was imaged by non-contact atomic force microscopy, which confirmed the formation of PA by resolving single chemical bond units. Angle-resolved photoemission spectroscopy suggests a semiconductor-to-metal transition through doping-induced suppression of the Peierls bond alternation of trans-PA on Cu(110). Electronically decoupled trans-PAs exhibit a band gap of 2.4 eV following copper oxide intercalation. Our study provides a platform for studying individual PA chains in real and reciprocal space, which may be further extended to study the intrinsic properties of non-linear excitons in conducting polymers.