Multiple Surface Optimizations for a Highly Durable LiCoO2 beyond 4.6 V

Recently, lots of researches have focused on enhancing the structure stability of LiCoO₂ (LCO) at a cutoff voltage of 4.6 V (vs Li/Li⁺) at room temperature. However, the high temperature (≥45 °C) performances are more significant for practical applications. Herein, the mechanism of unsatisfactory structure stability of LCO at 45 °C via comparing a commercial LCO (C-LCO) and a surface optimized LCO (O-LCO) is revealed first. The deteriorated structure stability of LCO at 45 °C is mainly due to two aspects: i) the promoted bulk Li⁺ ion diffusion kinetics at 45 °C leads to a higher state of charge for the charged LCO, which triggers more side reactions; ii) the more prominent surface structure collapse at 45 °C blocks the Li⁺ ion transport channels. Surface optimizations, including the anions (F⁻ and PO₄³⁻) and cations (Al³⁺) surface modulation and a subsurface spinel reinforcement, are comprehensively applied to alleviate the side reaction and structure collapse issues of O-LCO, leading to a high reversible discharge capacity of 238 mAh g⁻¹, as well as an obviously enhanced cycle and floating stability at 45 °C and beyond 4.6 V. A new insight is provided here for developing more advanced and practical high-voltage LCO.     

Enhanced Cycling Stability of 4.6 V LiCoO2 Cathodes by Inhibiting Catalytic Activity of its Interface Via MXene Modification

LiCoO₂ plays a key role in energy storage devices due to its high energy density. And the volumetric energy density of LiCoO₂ cathode can be significantly improved by increasing the charging cut-off voltage to 4.6 V. However, the increase in resistance at the LiCoO₂ interface, and the damage to the LiCoO₂ from the outside to the inside by the HF generated that caused by the decomposition of the organic electrolyte and LiPF₆ under 4.6 V conditions are not conducive to structural stability during cycling. Here, it is shown that the decomposition of electrolyte and LiPF₆ is effectively mitigated by inhibiting the interfacial catalytic activity of LiCoO₂ using an atomically thin layer of MXenes as a interlayer. Density functional theory results suggest that the decomposition energy of LiPF₆ is 1.13 and 3.21 eV at the interface of LiCoO₂ and MXenes, respectively. Time of Flight Secondary Ion Mass Spectrometry results further indicate that the decomposition products of the organic electrolyte and LiPF₆ have a thinner thickness at the interface of MXenes (5 nm) than LiCoO₂ (10 nm). This study provides a new and universal strategy for stabilizing the cathode interface to support the development of high energy density lithium-ion batteries.     

Adjusting the Redox Coupling Effect via Li/Co Anti-Site Defect for Stable High-Voltage LiCoO2 Cathode

High-voltage LiCoO₂ (LCO) is pressingly required for the portable electronics. But the O→Co charge transfer and the oxygen redox at high delithiation induce the issues of irreversible Co reduction, oxygen release, and unfavored phase transformation. Herein, it is proposed to tune the O→Co charge transfer via regulating Li/Co anti-site defect with Mg²⁺ and (PO₄)³⁻ co-doping to achieve a stable high-voltage LiCoO₂ cathode. The appropriately regulated Li/Co anti-site defect enhances the redox activity of the Co-ions, and inhibits the irreversibility of the oxygen redox and the coupled Co reduction. The increase of the formation energy of oxygen vacancies in the modified cathode at deep delithiation inhibits oxygen escape. Moreover, (PO₄)³⁻ doping also stabilizes oxygen-packed framework due to its strong bond energy with transition metal. These functions enhance the structural stability and the reversible Co/O redox ability. The improved cathode delivers a high capacity and long-cycle capacity retention on both 4.5 and 4.6 V. This study provides some insights into adjusting the redox coupling effect and enhancing the oxygen redox reversibility by Li/Co anti-site regulation.     

Large‐Scale Fabrication of MoS2 Ribbons and Their Light‐Induced Electronic/Thermal Properties: Dichotomies in the Structural and Defect Engineering

Controlled design and patterning of layered transition metal dichalcogenides (TMDs) into specific dimensions and geometries hold great potential for next‐generation micro/nanoscale electronic applications. Herein, the large‐scale fabrication of MoS₂ ribbons with widths ranging from micro‐ to nanoscale is reported. Their unique electric and thermal properties introduced by the shape change and defect creation are also demonstrated, with particular focus on the performance associated with light–matter interactions. The theoretical calculation indicates significantly increased absorption and scattering efficiency of the MoS₂ ribbons with decreasing width. As a result, enhanced photocarrier generation ability is detected on their phototransistors with defect‐modulated light‐response behavior. The light‐induced thermal transport properties of the MoS₂ ribbons are further studied. A decreased thermal conductivity is observed on narrower ribbons, attributed to the defects created during fabrication. It is also found that the effect of phonon scattering at ribbon edges on their thermal conductivity is insignificant, and the thermal transport has no obvious dependence on the ribbon direction at such width scale. This study evaluates the prospects for designing and fabricating TMD semiconductors with specific geometries for future optoelectronic applications.     

Sub-2 nm Ultrathin and Robust 2D FeNi Layered Double Hydroxide Nanosheets Packed with 1D FeNi-MOFs for Enhanced Oxygen Evolution Electrocatalysis

Water oxidation is a critical process for electrochemical water splitting due to its inherent sluggish kinetics. In spite of the high catalytic activities of noble metal-based electrocatalysts for water oxidation, their high cost, rare reserves, and low stabilities drive researchers to exploit efficient but low-cost electrocatalysts. Ultrathin 2D nanomaterials are considered efficient electrocatalysts for oxygen evolution reaction (OER) in water splitting. Herein, a facile strategy is proposed to fabricate 2D FeNi layered double hydroxide (FeNi-LDH) nanosheets packed with the in situ produced 1D sword-like FeNi-MOFs by using FeNi-LDH as a semi-sacrificial template. In the composite, the thickness of the formed nanosheets is only 1.34 nm, much thinner than that of most previously reported 2D materials. The 1D porous sword-like MOF nanorods have a long length of around 1.3 µm. Due to the unique 2D/1D combined structure, the as-prepared FeNi LDH/MOF is directly used as electrocatalyst for the OER displays enhanced OER electrocatalytic performance with a low overpotential of 272 mV@100 mA cm^–2, a small Tafel slope of 34.1 mV dec^–1, high long-term durability. This work provides a new way to fabricate integrated ultrathin 2D nanosheets and MOFs as advanced catalysts for electrochemical energy conversion.     

Generalized Synthetic Strategy for Amorphous Transition Metal Oxides-Based 2D Heterojunctions with Superb Photocatalytic Hydrogen and Oxygen Evolution

2D amorphous transition metal oxides (a-TMOs) heterojunctions that have the synergistic effects of interface (efficiently promoting the separation of electron−hole pairs) and amorphous nature (abundant defects and dangling bonds) have attracted substantial interest as compelling photocatalysts for solar energy conversion. Strategies to facilely construct a-TMOs-based 2D/2D heterojunctions is still a big challenge due to the difficulty of preparing individual amorphous counterparts. A generalized synthesis strategy based on supramolecular self-assembly for bottom–up growth of a-TMOs-based 2D heterojunctions is reported, by taking 2D/2D g-C₃N₄ (CN)/a-TMOs heterojunction as a proof-of-concept. This strategy primarily depends on controlling the cooperation of the growth of supramolecular precursor and the coordinated covalent bonds arising from the tendency of metal ions to attain the stable configuration of electrons, which is independent on the intrinsic character of individual metal ion, indicating it is universally applicable. As a demonstration, the structure, physical properties, and photocatalytic water-splitting performance of CN/a-ZnO heterojunction are systematically studied. The optimized 2D/2D CN/a-ZnO exhibits enhanced photocatalytic performance, the hydrogen (432.6 µmol h⁻¹ g⁻¹) and oxygen (532.4 µmol h⁻¹ g⁻¹) evolution rate are 15.5 and 12.2 times than bulk CN, respectively. This synthetic strategy is useful to construct 2D a-TMOs nanomaterials for applications in energy-related areas and beyond.     

MnO2 Gatekeeper: An Intelligent and O2‐Evolving Shell for Preventing Premature Release of High Cargo Payload Core,Overcoming Tumor Hypoxia,and Acidic H2O2‐Sensitive MRI

Premature leakage of photosensitizer (PS) from nanocarriers significantly reduces the accumulation of PS within a tumor, thereby enhancing nonspecific accumulation in normal tissues, which inevitably leads to a limited efficacy for photodynamic therapy (PDT) and the enhanced systematic phototoxicity. Moreover, local hypoxia of the tumor tissue also seriously hinders the PDT. To overcome these limitations, an acidic H₂O₂‐responsive and O₂‐evolving core–shell PDT nanoplatform is developed by using MnO₂ shell as a switchable shield to prevent the premature release of loaded PS in core and elevate the O₂ concentration within tumor tissue. The inner core SiO₂‐methylene blue obtained by co‐condensation has a high PS payload and the outer MnO₂ shell shields PS from leaking into blood after intravenous injection until reaching tumor tissue. Moreover, the shell MnO₂ simultaneously endows the theranostic nanocomposite with redox activity toward H₂O₂ in the acidic microenvironment of tumor tissue to generate O₂ and thus overcomes the hypoxia of cancer cells. More importantly, the Mn(ΙΙ) ion reduced from Mn(ΙV) is capable of in vivo magnetic resonance imaging selectively in response to overexpressed acidic H₂O₂. The facile incorporation of the switchable MnO₂ shell into one multifunctional diagnostic and therapeutic nanoplatform has great potential for future clinical application.     

Heteroatom (N or N‐S)‐Doping Induced Layered and Honeycomb Microstructures of Porous Carbons for CO2 Capture and Energy Applications

Increasing global challenges such as climate change, environmental pollution, and energy shortage have stimulated the worldwide explorations into novel and clean materials for their applications in the capture of carbon dioxide, a major greenhouse gas, and toxic pollutants, energy conversion, and storage. In this study, two microstructured carbons, namely N‐doped pillaring layered carbon (NC) and N, S codoped honeycomb carbon (NSC), have been fabricated through a one‐pot pyrolysis process of a mixture containing glucose, sodium bicarbonate, and urea or thiourea. The heteroatom doping is found to induce tailored microstructures featuring highly interconnected pore frameworks, high sp²‐C ratios, and high surface areas. The formation mechanism of the varying pore frameworks is believed to be hydrogen‐bond interactions. NSC displays a similar CO₂ adsorption capacity (4.7 mmol g^?1 at 0 °C), a better CO₂/N₂ selectivity, and higher activity in oxygen reduction reaction as compared with NC‐3 (the NC sample with the highest N content of 7.3%). NSC favors an efficient four‐electron reduction pathway and presents better methanol tolerance than Pt/C in alkaline media. The porous carbons also exhibit excellent rate performance as supercapacitors.     

Well‐Ordered Large‐Pore Mesoporous Anatase TiO2 with Remarkably High Thermal Stability and Improved Crystallinity: Preparation,Characterization, and Photocatalytic Performance

Thermally‐stable, ordered mesoporous anatase TiO₂ with large pore size and high crystallinity has been successfully synthesized through an evaporation‐induced self‐assembly technique, combined with encircling ethylenediamine (EN) protectors to maintain the liquid crystal mesophase structure of TiO₂ primary particles, followed by calcination at higher temperature. The structures of the prepared mesoporous TiO₂ are characterized in detail by small‐angle and wide‐angle X‐ray diffraction, Raman spectra, N₂ adsorption/desorption isotherms, and transmission electron microscopy. Experimental results indicate that the well‐ordered mesoporous structure could be maintained up to 700 °C (M700) and also possesses large pore size (10 nm), high specific BET surface area (122 m² g^?1), and high total pore volumes (0.20 cm³ g^?1), which is attributed to encircling EN protectors for maintaining the mesoporous framework against collapsing, inhibiting undesirable grain growth and phase transformation during the calcination process. A possible formation mechanism for the highly stable large‐pore mesoporous anatase TiO₂ is also proposed here, which could be further confirmed by TG/FT‐IR in site analysis and X‐ray photoelectron spectroscopy. The obtained mesoporous TiO₂ of M700 exhibit better photocatalytic activity than that of Degussa P25 TiO₂ for degradation of highly toxic 2,4‐dichlorophenol under UV irradiation. This enhancement is attributed to the well‐ordered large‐pore mesoporous structure, which facilitates mass transport, the large surface area offering more active sites, and high crystallinity that favors the separation of photogenerated electron‐hole pairs, confirmed by surface photovoltage spectra.     

Understanding the Synergistic Effects of Cobalt Single Atoms and Small Nanoparticles: Enhancing Oxygen Reduction Reaction Catalytic Activity and Stability for Zinc-Air Batteries

The development of earth-abundant oxygen reduction reaction (ORR) catalysts with high catalytic activity and good stability for practical metal-air batteries remains an enormous challenge. Herein, a highly efficient and durable ORR catalyst is reported, which consists of atomically dispersed Co single atoms (Co-SAs) in the form of Co-N4 moieties and small Co nanoparticles (Co-SNPs) co-anchored on nitrogen-doped porous carbon nanocage (Co-SAs/SNPs@NC). Benefiting from the synergistic effect of Co-SAs and Co-SNPs as well as the enhanced anticorrosion capability of the carbon matrix brought by its improved graphitization degree, the resultant Co-SAs/SNPs@NC catalyst exhibits outstanding ORR activity and remarkable stability in alkaline media, outperforming Co-SAs-based catalyst (Co-SAs@NC), and benchmark Pt/C catalyst. Density functional theory calculations reveal that the strong interaction between Co-SNPs and Co-N4 sites can increase the valence state of the active Co atoms in Co-SAs/SNPs@NC and moderate the adsorption free energy of ORR intermediates, thus facilitating the reduction of O₂. Moreover, the practical zinc-air battery assembled with Co-SAs/SNPs@NC catalyst demonstrates a maximum power density of 223.5 mW cm^–2, a high specific capacity of 742 W h kg^–1 at 50 mA cm^–2 and a superior cycling stability.     

High Tg Cyclic Olefin Copolymer Gate Dielectrics for N,N′‐Ditridecyl Perylene Diimide Based Field‐Effect Transistors: Improving Performance and Stability with Thermal Treatment

A novel application of ethylene‐norbornene cyclic olefin copolymers (COC) as gate dielectric layers in organic field‐effect transistors (OFETs) that require thermal annealing as a strategy for improving the OFET performance and stability is reported. The thermally‐treated N,N′‐ditridecyl perylene diimide (PTCDI‐C13)‐based n‐type FETs using a COC/SiO₂ gate dielectric show remarkably enhanced atmospheric performance and stability. The COC gate dielectric layer displays a hydrophobic surface (water contact angle = 95° ± 1°) and high thermal stability (glass transition temperature = 181 °C) without producing crosslinking. After thermal annealing, the crystallinity improves and the grain size of PTCDI‐C13 domains grown on the COC/SiO₂ gate dielectric increases significantly. The resulting n‐type FETs exhibit high atmospheric field‐effect mobilities, up to 0.90 cm² V^?1 s^?1 in the 20 V saturation regime and long‐term stability with respect to H₂O/O₂ degradation, hysteresis, or sweep‐stress over 110 days. By integrating the n‐type FETs with p‐type pentacene‐based FETs in a single device, high performance organic complementary inverters that exhibit high gain (exceeding 45 in ambient air) are realized.     

New Strategy for Polysulfide Protection Based on Atomic Layer Deposition of TiO2 onto Ferroelectric‐Encapsulated Cathode: Toward Ultrastable Free‐Standing Room Temperature Sodium–Sulfur Batteries

The room temperature (RT) sodium–sulfur batteries (Na–S) hold great promise for practical applications including energy storage and conversion due to high energy density, long lifespan, and low cost, as well based on the abundant reserves of both sodium metal and sulfur. Herein, freestanding (C/S/BaTiO₃)@TiO₂ (CSB@TiO₂) electrode with only ≈3 wt% of BaTiO₃ additive and ≈4 nm thickness of amorphous TiO₂ atomic layer deposition protective layer is rational designed, and first used for RT Na–S batteries. Results show that such cathode material exhibits high rate capability and excellent durability compared with pure C/S and C/S/BaTiO₃ electrodes. Notably, this CSB@TiO₂ electrode performs a discharge capacity of 524.8 and 382 mA h g^?1 after 1400 cycles at 1 A g^?1 and 3000 cycles at 2 A g^?1, respectively. Such superior electrochemical performance is mainly attributed from the “BaTiO₃‐C‐TiO₂” synergetic structure within the matrix, which enables effectively inhibiting the shuttle effect, restraining the volumetric variation and stabilizing the ionic transport interface.     

Comprehensive Understanding of the Spatial Configurations of CeO2 in NiO for the Electrocatalytic Oxygen Evolution Reaction: Embedded or Surface‐Loaded

Introducing cerium (Ce) species into electrocatalysts has been recently developed as an effective approach to improve their oxygen evolution reaction (OER) performance. Importantly, the spatial distribution of Ce species in the hosts can determine the availability of Ce species either as additives or as co‐catalysts, which would dictate their different contributions to the enhanced electrocatalytic performance. Herein, the comprehensive investigations on two different catalyst configurations, namely CeO₂‐embedded NiO (Ce‐NiO‐E) and CeO₂‐surface‐loaded NiO (Ce‐NiO‐L), are performed to understand the effect of their specific spatial arrangements on OER characteristics. The Ce‐NiO‐E catalysts exhibit a smaller overpotential of 382 mV for 10 mA cm^?2 and a lower Tafel slope of 118.7 mV dec^?1, demonstrating the benefits of the embedded configuration for OER, as compared with those of Ce‐NiO‐L (426 mV and 131.6 mV dec^?1) and pure NiO (467 mV and 140.7 mV dec^?1), respectively. The improved OER property of Ce‐NiO‐E originates from embedding small‐sized CeO₂ clusters into the host for the larger specific surface area, richer surface defects, higher oxygen adsorption capacity, and better optimized electronic structures of the surface active sites, as compared with Ce‐NiO‐L. Above findings provide a valuable guideline for and insight in designing catalysts with different spatial configurations for enhanced catalytic properties.     

A Surface Tailoring Method of Ultrathin Polymer Gate Dielectrics for Organic Transistors: Improved Device Performance and the Thermal Stability Thereof

Tailoring the surface of the dielectric layer is of critical importance to form a good interface with the following channel layer for organic thin film transistors (OTFTs). Here, a simple surface treatment method is applied onto an ultrathin (<15 nm) organosilicon‐based dielectric layer via the initiated chemical vapor deposition (iCVD) to make it compatible with organic semiconductors without degrading its insulating property. A molecular‐thin oxide capping layer is formed on a 15 nm thick poly(1,3,5‐trimetyl‐1,3,5‐trivinyl cyclotrisiloxane) (pV3D3) by a brief oxygen plasma treatment. The capping layer greatly enhances the thermal stability of the dielectrics, without degrading the original mechanical flexibility and insulating performance of the dielectrics. Moreover, the surface silanol functionalities formed by the plasma treatment can also be utilized for the surface modification with silane compounds. The surface‐modified dielectrics are applied to fabricate low‐voltage operating (<5 V) pentacene‐based OTFTs. The highest field‐effect mobility of the device with the surface‐treated 15 nm thick pV3D3 is 0.59 cm² V^?1 s^?1, which is improved up to two times compared to the TFT with the pristine pV3D3. It is believed that the simple surface treatment method can widely extend the applicability of the highly robust, ultrathin, and flexible pV3D3 gate dielectrics to design the surface of the dielectrics to match well various kinds of organic semiconductors.     

Synthesis of Leaf‐Vein‐Like g‐C3N4 with Tunable Band Structures and Charge Transfer Properties for Selective Photocatalytic H2O2 Evolution

Photocatalytic H₂O₂ evolution through two‐electron oxygen reduction has attracted wide attention as an environmentally friendly strategy compared with the traditional anthraquinone or electrocatalytic method. Herein, a biomimetic leaf‐vein‐like g‐C₃N₄ as an efficient photocatalyst for H₂O₂ evolution is reported, which owns tenable band structure, optimized charge transfer, and selective two‐electron O₂ reduction. The mechanism for the regulation of band structure and charge transfer is well studied by combining experiments and theoretical calculations. The H₂O₂ yield of CN4 (287 µmol h^?1) is about 3.3 times higher than that of pristine CN (87 µmol h^?1), and the apparent quantum yield for H₂O₂ evolution over CN4 reaches 27.8% at 420 nm, which is much higher than that for many other current photocatalysts. This work not only provides a novel strategy for the design of photocatalyst with excellent H₂O₂ evolution efficiency, but also promotes deep understanding for the role of defect and doping sites on photocatalytic activity.     

A Low‐Toxic Multifunctional Nanoplatform Based on Cu9S5@mSiO2 Core‐Shell Nanocomposites: Combining Photothermal‐ and Chemotherapies with Infrared Thermal Imaging for Cancer Treatment

Copper chalcogenides have been demonstrated to be a promising photothermal agent due to their high photothermal conversion efficiency, synthetic simplicity, and low cost. However, the hydrophobic and less biocompatible characteristics associated with their synthetic processes hamper widely biological applications. An alternative strategy for improving hydrophilicity and biocompatibility is to coat the copper chalcogenide nanomaterials with silica shell. Herein, the rational preparation design results in successful coating mesoporous silica (mSiO₂) on as‐synthesized Cu₉S₅ nanocrystals, forming Cu₉S₅@mSiO₂‐PEG core‐shell nanostructures. As‐prepared Cu₉S₅@mSiO₂‐PEG core‐shell nanostructures show low cytotoxicity and excellent blood compatibility, and are effectively employed for photothermal ablation of cancer cells and infrared thermal imaging. Moreover, anticancer drug of doxorubicin (DOX)‐loaded Cu₉S₅@mSiO₂‐PEG core‐shell nanostructures show pH sensitive release profile and are therefore beneficial to delivery of DOX into cancer cells for chemotherapy. Importantly, the combination of photothermal‐ and chemotherapies demonstrates better effects of therapy on cancer treatment than individual therapy approaches in vitro and in vivo.     

Cocatalyst‐Free Photocatalysts for Efficient Visible‐Light‐Induced H2 Production: Porous Assemblies of CdS Quantum Dots and Layered Titanate Nanosheets

Highly efficient, visible‐light‐induced H₂ generation can be achieved without the help of a Pt cocatalyst by new hybrid photocatalysts, in which CdS quantum dots (QDs) (particle size ≈2.5 nm) are incorporated in the porous assembly of sub‐nanometer‐thick layered titanate nanosheets. Due to the very‐limited crystal dimension of component semiconductors, the electronic structure of CdS QDs is strongly coupled with that of the layered titanate nanosheets, leading to an efficient electron transfer between them and the enhancement of the CdS photostability. As a consequence of the promoted electron transfer, the photoluminescence of CdS QDs is nearly quenched after hybridization, indicating the almost‐suppression of electron‐hole recombination. These Pt‐cocatalyst‐free, CdS‐layered titanate nanohybrids show much‐higher photocatalytic activity for H₂ production than the precursor CdS QDs and layered titanate, which is due to the increased lifetime of the electrons and holes, the decrease of the bandgap energy, and the expansion of the surface area upon hybridization. The observed photocatalytic efficiency of these Pt‐free hybrids (≈1.0 mmol g^?1 h^?1) is much greater than reported values of other Pt‐free CdS‐TiO₂ systems. This finding highlights the validity of 2D semiconductor nanosheets as effective building blocks for exploring efficient visible‐light‐active photocatalysts for H₂ production.