Stability of Li1.3Al0.3Ti1.7(PO4)3-Based Composite Electrolytes against Lithium Anodes Enhanced by Uniform Surface Coating of Two-Dimensional Graphene-like C3N4 on Particle Surfaces.

All-solid-state lithium (Li) batteries have attracted considerable interest due to their potential in high energy density as well as safety. However, the realization of a stable Li/solid-state electrolyte (SSE) interface remains challenging. Herein, two-dimensional graphene-like C3N4 (g-C3N4) as a coating layer on Li1.3Al0.3Ti1.7(PO4)3 (LATP) electrolyte (LATP@CN) has been applied to construct the stable Li/SSE interface. The g-C3N4 layer is uniformly coated on the LATP surface using the in situ calcination method, which not only enhances the dispersibility of LATP particles in poly(ethylene oxide) (PEO) through the interaction between surface functional groups but also suppresses the side reactions between Li and LATP. The coating layer can effectively improve the interfacial stability. As a result, the conductivity and stability of the obtained composite solid-state electrolytes (CSEs) against Li are enhanced. The Li∥CSEs∥Li symmetric cells stably cycle for 670 and 600 h at 0.1 and 0.2 mA cm-2, respectively. The Li∥CSEs∥LiFePO4 cells stably cycle more than 100 times at 0.1 and 0.2 C with a capacity retention rate of about 86% and 88%, respectively. This work inspires a new strategy to avoid the reactions between LATP and Li.

Ion Transport Behavior in van der Waals Gaps of 2D Materials.

2D materials, with advantages of atomic thickness and novel physical/chemical characteristics, have emerged as the vital building blocks for advanced lamellar membranes which possess promising potential in energy storage, ion separation, and catalysis. When 2D materials are stacked together, the van der Waals (vdW) force generated between adjacent layered nanosheets induces the construction of an ordered lamellar membrane. By regulating the interlayer spacing down to the nanometer or even sub-nanometer scale, rapid and selective ion transport can be achieved through such vdW gaps. The further improvement and application of qualified 2D materials-based lamellar membranes (2DLMs) can be fulfilled by the rational design of nanochannels and the intelligent micro-environment regulation under different stimuli. Focusing on the newly emerging advances of 2DLMs, in this review, the common top-down and bottom-up synthesis approaches of 2D nanosheets and the design strategy of functional 2DLMs are briefly introduced. Two essential ion transport mechanisms within vdW gaps are also involved. Subsequently, the responsive 2DLMs based on different types of external stimuli and their unique applications in nanofluid transport, membrane-based filters, and energy storage are presented. Based on the above analysis, the existing challenges and future developing prospects of 2DLMs are further proposed.

Fast Lithium Ion Transport Pathways Constructed by Two-Dimensional Boron Nitride Nanoflakes in Quasi-Solid-State Polymer Electrolyte.

Quasi-solid-state electrolytes (QSSEs) are gaining huge popularity because of their significantly improved safety performance over nonaqueous liquid electrolytes and superior process adaptability over all-solid-state electrolytes. However, because of the existence of liquid molecules, QSSEs typically have low lithium ion transference numbers and compromised thermal stability. In this work, we present the fabrication of a well-rounded QSSE by introducing hexagonal boron nitride nanoflakes (BNNFs) as an inorganic filler in a poly(vinylene carbonate) matrix. BNNFs, in contrast to most inorganic fillers used as anion trappers, are used to build fast lithium ion transport pathways directly on their two-dimensional surfaces. We confirm the attractive coupling between lithium ions and BNNFs, and we confirm that with the help of BNNFs, lithium ions can migrate with less damping and a lower transport energy barrier. As a result, the designed electrolyte exhibits good ion transportability, promoted fire retardancy, and good compatibility with lithium metal anodes and commercial cathodes.

Single atom catalysts in Van der Waals gaps.

Single-atom catalysts provide efficiently utilized active sites to improve catalytic activities while improving the stability and enhancing the activities to the level of their bulk metallic counterparts are grand challenges. Herein, we demonstrate a family of single-atom catalysts with different interaction types by confining metal single atoms into the van der Waals gap of two-dimensional SnS2. The relatively weak bonding between the noble metal single atoms and the host endows the single atoms with more intrinsic catalytic activity compared to the ones with strong chemical bonding, while the protection offered by the layered material leads to ultrahigh stability compared to the physically adsorbed single-atom catalysts on the surface. Specifically, the trace Pt-intercalated SnS2 catalyst has superior long-term durability and comparable performance to that of commercial 10 wt% Pt/C catalyst in hydrogen evolution reaction. This work opens an avenue to explore high-performance intercalated single-atom electrocatalysts within various two-dimensional materials.

Three-Dimensional Fe Single-Atom Catalyst for High-Performance Cathode of Zn-Air Batteries.

Designing cost-effective and highly active oxygen reduction reaction (ORR) catalysts is critical for the development of Zn-air batteries (ZABs). Iron-nitrogen-carbon (Fe-N-C) catalysts with single-atom Fe-Nx active sites are considered as one of the most promising alternatives to noble Pt but are hindered by unsatisfactory activity and durability. Herein, a NaCl template-assisted in situ pyrolysis technique is utilized to massively fabricate Fe-N-C single-atom catalysts (SACs) anchored on the three-dimensional open-pore carbon networks (denoted as 3D SAFe). The 3D SAFe catalyst exhibits ultrahigh activity with a half-wave potential of 0.90 V (vs RHE), benefiting from the enhanced mass diffusion and the increased amount of effective Fe-N4 sites. Consequently, the ZABs assembled with 3D SAFe deliver high peak power density up to 156 mW cm-2 and outstanding durability of 80 h, suggesting the application potential of the 3D SAFe catalyst. This work inspires the rational design and synthesis of highly efficient SACs for ZABs.

Electrochemical CO2 reduction to ethylene by ultrathin CuO nanoplate arrays.

Electrochemical reduction of CO2 to multi-carbon fuels and chemical feedstocks is an appealing approach to mitigate excessive CO2 emissions. However, the reported catalysts always show either a low Faradaic efficiency of the C2+ product or poor long-term stability. Herein, we report a facile and scalable anodic corrosion method to synthesize oxygen-rich ultrathin CuO nanoplate arrays, which form Cu/Cu2O heterogeneous interfaces through self-evolution during electrocatalysis. The catalyst exhibits a high C2H4 Faradaic efficiency of 84.5%, stable electrolysis for ~55 h in a flow cell using a neutral KCl electrolyte, and a full-cell ethylene energy efficiency of 27.6% at 200 mA cm-2 in a membrane electrode assembly electrolyzer. Mechanism analyses reveal that the stable nanostructures, stable Cu/Cu2O interfaces, and enhanced adsorption of the *OCCOH intermediate preserve selective and prolonged C2H4 production. The robust and scalable produced catalyst coupled with mild electrolytic conditions facilitates the practical application of electrochemical CO2 reduction.

Constructing Artificial SEI Layer on Lithiophilic MXene Surface for High-Performance Lithium Metal Anodes.

MXene has been found as a good host for lithium (Li) metal anodes because of its high specific surface area, lithiophilicity, good stability with lithium, and the in situ formed LiF protective layer. However, the formation of Li dendrites and dead Li is inevitable during long-term cycle due to the lack of protection at the Li/electrolyte interface. Herein, a stable artificial solid electrolyte interface (SEI) is constructed on the MXene surface by using insulating g-C3 N4 layer to regulate homogeneous Li plating/stripping. The 2D/2D MXene/g-C3 N4 composite nanosheets can not only guarantee sufficient lithiophilic sites, but also protect the Li metal from continuous corrosion by electrolytes. Thus, the Ti3 C2 Tx /g-C3 N4 electrode enables conformal Li deposition, enhanced average Coulombic efficiency (CE) of 98.4%, and longer cycle lifespan over 400 cycles with an areal capacity of 1.0 mAh cm-2 at 0.5 mA cm-2 . Full cells paired with LiFePO4 (LFP) cathode also achieve enhanced rate capacity and cycling stability with higher capacity retention of 85.5% after 320 cycles at 0.5C. The advantages of the 2D/2D lithiophilic layer/artificial SEI layer heterostructures provide important insights into the design strategies for high-performance and stable Li metal batteries.

Self-Healing Nucleation Seeds Induced Long-Term Dendrite-Free Lithium Metal Anode.

Seeded lithium (Li) nucleation has been considered as a promising strategy to achieve uniform Li deposition. However, problems of agglomeration and pulverization quickly invalidate the nucleation seeds, resulting in Li dendrite growth during repeated charge/discharge processes. Herein, liquid gallium-indium (GaIn) nanoparticles with structural self-healing properties are utilized to guide uniform metallic Li nucleation and deposition. Ultrafine GaIn nanoparticles (∼25 nm) uniformly decorated on the surface of carbon layers effectively homogenize the lithium-ion flux. After fully Li stripping, lithiophilic GaIn nanoparticles return to the liquid binary eutectic phase, thereby healing the deformed structure and enabling them to continuously guide dendrite-free Li deposition. Li metal anodes with such nucleation seeds exhibit nearly zero nucleation overpotential even after hundreds of cycles and a high average Coulombic efficiency of 99.03% for more than 400 cycles. The design of self-healing nucleation seeds provides important insights for obtaining high-performance lithium metal anodes.

Ni(OH)2 Templated Synthesis of Ultrathin Ni3 S2 Nanosheets as Bifunctional Electrocatalyst for Overall Water Splitting.

Ultrathin nickel (Ni)-based sulfide nanosheets have been reported as excellent electrocatalysts for overall water splitting; however, the uncontrollability over thickness due to the nonlayered structure still hampers its practical application. Herein, a simple topochemical conversion strategy is employed to synthesize cobalt-doped Ni3 S2 (Co-Ni3 S2 ) ultrathin nanosheets on Ni foam. The Co-Ni3 S2 nanosheets are controlled synthesized by using Co-Ni(OH)2 ultrathin nanosheets as templates with anneal and sulfurization treatment, showing exceptional electrocatalytic activity. This template-assisted method can also be applied to obtain Ni, NiO, and NiPx nanosheets, providing a universal strategy to synthesize ultrathin nanosheets of nonlayered materials. The overall water splitting of this Co-Ni3 S2 ultrathin nanosheets achieves a low voltage of 1.54 V at a current density of 10 mA cm-2 and high durability in 1 m KOH, comparable to the best performance of electrochemical water splitting ever reported. The detailed structural transformation of Ni-based sulfides in the catalytic process and its mechanism are further explored both experimentally and theoretically.

3D Artificial Solid-Electrolyte Interphase for Lithium Metal Anodes Enabled by Insulator-Metal-Insulator Layered Heterostructures.

Despite considerable efforts to prevent lithium (Li) dendrite growth, stable cycling of Li metal anodes with various structures remains extremely difficult due to the direct contact of the liquid electrolyte with Li. Rational design of solid-electrolyte interphase (SEI) for 3D electrodes is a promising but still challenging strategy for preventing Li dendrite growth and avoiding lithium-electrolyte side reactions in Li-metal batteries. Here, a 3D architecture is constructed with g-C3 N4 /graphene/g-C3 N4 insulator-metal-insulator sandwiched nanosheets to guide uniform Li plating/stripping in the van der Waals gap between the graphene and the g-C3 N4 , and the function of which can be regarded as a 3D artificial SEI. Li deposition on the surface of g-C3 N4 is suppressed due to its insulating nature. However, its uniform lithiophilic sites and nanopore channels enable homogeneous lithium plating between the graphene and the g-C3 N4 , prohibiting the direct contact of the electrolyte with the Li metal. The use of the g-C3 N4 -layer-modified 3D anode enables long-term Li deposition with a high Coulombic efficiency and stable cycling of full cells under high cathode loading, limited Li excess, and lean electrolyte conditions. The concept of a 3D artificial SEI will shed light on developing safe and stable Li-metal anodes.

In-Situ Formed Protecting Layer from Organic/Inorganic Concrete for Dendrite-Free Lithium Metal Anodes.

In this work, a separator modified by composite material of graphite fluoride nanosheets and poly(vinylidene difluoride) (GFNs-PVDF) is fabricated to in-situ construct a protective layer on Li metal anodes. The much-improved mechanical properties of this organic/inorganic protecting layer ensure efficient restriction on the growth of Li dendrites. The LiF and graphene nanosheets generated by the reaction of GFNs with lithium metal can not only provide fast transport channels for Li ions but also protect the Li metal anode from continuous corrosion of electrolytes. In addition, GFNs' lithiophilic nature guarantees the uniform Li nucleation site and perfect contact between li metal and the protecting layer without void space, leading to a low interfacial impedance and layer-by-layer lithium deposition. Together with the scalable method and cheap raw materials, this strategy provides new insights toward practical applications of Li metal batteries.

Large-Scale Modification of Commercial Copper Foil with Lithiophilic Metal Layer for Li Metal Battery.

The application and development of lithium metal battery are severely restricted by the uncontrolled growth of lithium dendrite and poor cycle stability. Uniform lithium deposition is the core to solve these problems, but it is difficult to be achieved on commercial Cu collectors. In this work, a simple and commercially viable strategy is utilized for large-scale preparation of a modified planar Cu collector with lithiophilic Ag nanoparticles by a simple substitution reaction. As a result, the Li metal shows a cobblestone-like morphology with similar size and uniform distribution rather than Li dendrites. Interestingly, a high-quality solid electrolyte interphase layer in egg shell-like morphology with fast ion diffusion channels is formed on the interface of the collector, exhibiting good stability with long-term cycles. Moreover, at the current density of 1 mA cm-2 for 1 mAh cm-2 , the Ag modified planar Cu collector shows an ultralow nucleation overpotential (close to 0 mV) and a stable coulombic efficiency of 98.54% for more than 600 cycles as well as long lifespan beyond 900 h in a Li|Cu-Ag@Li cell, indicating the ability of this method to realize stable Li metal batteries. Finally, full cells paired with LiNi0.8 Co0.1 Mn0.1 O2 show superior rate performance and stability compared with those paired with Li foil.

Photoelectrochemical properties and the detection mechanism of Bi2WO6 nanosheet modified TiO2 nanotube arrays.

Bi2WO6 nanosheet modified TiO2 nanotube arrays were synthesized by an anodization method combined with sequential chemical bath deposition for enhancement of the photoelectrochemical detection performance. The structures, morphologies and elemental compositions of the nanotube arrays were characterized with X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectrometry. Bi2WO6 nanosheets were successfully deposited on the tube walls of TiO2 nanotubes. The photoelectrochemical property of Bi2WO6/TiO2 NTAs was determined with chronoamperometry and cyclic voltammetry using an electrochemical workstation equipped with a UV LED light (365 nm). The optimum detection sensitivity of glucose in water was determined to be 0.244 µA mM(-1) in the linear range from 0 to 2500 µM. Bi2WO6 modification on TiO2 NTAs simultaneously decreased the background photocurrent and increased the current response to organics, resulting in the enhancement of photoelectrochemical detection properties. Mechanisms of the Bi2WO6 modification are discussed by analyzing the photoelectrochemical processes, including optical absorption, charges transfer and surface electrochemical reactions. Direct oxidation by holes rather than indirect oxidation by ˙OH radicals is believed to be a key role in this enhancement.