Confining Polymer Electrolyte in MOF for Safe and High-Performance All-Solid-State Sodium Metal Batteries.

Nanoconfined polymer molecules exhibit profound transformations in their properties and behaviors. Here, we present the synthesis of a polymer-in-MOF single ion conducting solid polymer electrolyte, where polymer segments are partially confined within nanopores ZIF-8 particles through Lewis acid-base interactions for solid-state sodium-metal batteries (SSMBs). The unique nanoconfinement effectively weakens Na ion coordination with the anions, facilitating the Na ion dissociation from salt. Simultaneously, the well-defined nanopores within ZIF-8 particles provide oriented and ordered migration channels for Na migration. As a result, this pioneering design allows the solid polymer electrolyte to achieve a Na ion transference number of 0.87, Na ion conductivity of 4.01×10-4 S cm-1, and an extended electrochemical voltage window up to 4.89 V vs. Na/Na+. The assembled SSMBs (with Na3V2(PO4)3 as the cathode) exhibit dendrite-free Na-metal deposition, promising rate capability, and stable cycling performance with 96 % capacity retention over 300 cycles. This innovative polymer-in-MOF design offers a compelling strategy for advancing high-performance and safe solid-state metal battery technologies.

A Deeper Understanding of Metal Nucleation and Growth in Rechargeable Metal Batteries Through Theory and Experiment.

Lithium and sodium metal batteries continue to occupy the forefront of battery research. Their exceptionally high energy density and nominal voltages are highly attractive for cutting-edge energy storage applications. Anode-free metal batteries are also coming into the research spotlight offering improved safety and even higher energy densities than conventional metal batteries. However, uneven metal nucleation and growth which leads to dendrites continues to limit the commercialisation of conventional and anode-free metal batteries alike. This review connects models and theories from well-established fields in metallurgy and electrodeposition to both conventional and anode-free metal batteries. These highly applicable models and theories explain the driving forces of uneven metal growth and can inform future experiment design. Finally, the models and theories that are most relevant to each anode-related cell component are identified. Keeping these specific models and theories in mind will assist with rational design for these components.

Solvent-derived Fluorinated Secondary Interphase for Reversible Zn-graphite Dual-ion Batteries.

The irreversibility of anion intercalation-deintercalation is a fundamental issue in determining the cycling stability of a dual-ion battery (DIB). In this work, we demonstrate that using a partially fluorinated carbonate solvent can drive a beneficial fluorinated secondary interphase layer formation. Such layer facilitates reversible anion (de-)intercalation processes by impeding solvent molecule co-intercalation and the associated graphite exfoliation. The enhanced reversibility of anion transport contributes to the overall cycling stability for a Zn-graphite DIB-a high Coulombic efficiency of 98.5 % after 800 cycles, with an attractive discharge capacity of 156 mAh g-1 and a mid-point discharge voltage of ≈1.7 V (at 0.1 A g-1 ). In addition, the formed fluorinated secondary interphase suppresses the self-discharge behavior, preserving 29 times of the capacity retention rate compared to the battery with a commonly used carbonate solvent, after standing for 24 hours. This work provides a simple and effective strategy for addressing the critical challenges in graphite-based DIBs and contributes to fundamental understanding to help accelerate their practical application.

Nanoconfined Topochemical Conversion from MXene to Ultrathin Non-Layered TiN Nanomesh toward Superior Electrocatalysts for Lithium-Sulfur Batteries.

2D non-layered materials (2DNLMs) featuring massive undercoordinated surface atoms and obvious lattice distortion have shown great promise in catalytic/electrocatalytic applications, but their controllable synthesis remains challenging. Here, a new type of ultrathin carbon-wrapped titanium nitride nanomesh (TiN NM@C) is prepared using a rationally designed nano-confinement topochemical conversion strategy. The ultrathin 2D geometry with well-distributed pores offers TiN NM@C plentiful exposed active sites and rapid charge transfer, leading to outstanding electrocatalytic performance tackling the sluggish sulfur redox kinetics in lithium-sulfur batteries (LSBs). LSBs employing TiN NM@C electrocatalyst deliver excellent rate capabilities (e.g., 304 mAh g-1 at 10 C), greatly outperforming that of using TiN nanoparticles embedded in carbon nanosheets (TiN NPs@C) as a benchmark. More impressively, a free-standing electrode for LSBs with a high sulfur loading of 7.3 mg cm-2 is demonstrated, showing a high peak areal capacity of 5.6 mAh cm-2 at a high current density of 6.1 mA cm-2 . This work provides a new avenue for the facile and controllable fabrication of 2DNLMs with impressive electrocatalysis for LSBs as well as other energy conversion and storage technologies.

A Study of Membrane Impact on Spatial Resolution of Liquid In Situ Transmission Electron Microscope.

Microchip technology with electron transparent membranes is a key component for in situ liquid transmission electron microscope (TEM) characterization. The membranes can significantly influence the TEM imaging spatial resolution, not only due to introducing additional material layers but also due to the associated bulging. The membrane bulging is largely defined by the membrane materials, thickness, and short dimension. The impact of the membrane on the spatial resolution, especially the extent of its bulging, was systematically investigated through the impact on the signal-to-noise ratio, chromatic aberration, and beam broadening. The optimization of the membrane parameters is the key component when designing the in situ TEM liquid cell. The optimal membrane thickness of 50 nm was found which balances the impact of membrane bulging and membrane thickness. Beyond this, the short membrane window dimension and the chip nominal spacing should be minimized. However, these two parameters have practical limitations in regards to chip handling.

An Integrated Strategy towards Enhanced Performance of the Lithium-Sulfur Battery and its Fading Mechanism.

To fulfil the potential of Li-S batteries (LSBs) with high energy density and low cost, multiple challenges need to be addressed simultaneously. Most research in LSBs has been focused on the sulfur cathode design, although the performance is also known to be sensitive to other parameters such as binder, current collector, separator, lithium anode, and electrolyte. Here, an integrated LSB system based on the understanding of the different roles of binder, current collector, and separator is developed. By using the cross-linked carboxymethyl cellulose-citric acid (CMC-CA) binder, Toray carbon paper current collector, and reduced graphene oxide (rGO) coated separator, LSBs achieve a high capacity of 960 mAh g-1 after 200 cycles (2.5 mg cm-2 ) and 930 mAh g-1 after 50 cycles (5 mg cm-2 ) at 0.1 C. Moreover, the failure mechanism at a high sulfur loading with characteristics of fast capacity decay and infinite charging is discussed. This work highlights the synergistic effect of different components and the challenges towards more reliable LSBs with high sulfur loading.

Study of Na Deposition Formation in Mixed Ethylene: Propylene Carbonate Electrolytes by Inert/Cryoelectron Microscopy.

The sodium anode-free combines low-cost and high energy density, demonstrating a promising alternative to the Li battery counterpart. Nevertheless, the uptake of a sodium anode-free battery is greatly impeded by the uncontrollable dendrite proliferation upon the chemically active metallic Na. An insightful mechanistic understanding of Na deposition nucleation and growth behavior in ethylene carbonate and propylene carbonate (EC/PC, 1:1) is revealed via various inert and/or cryo-electron microscopy characterization techniques. The deposit morphology, size, and distribution were studied with different current densities and areal capacity. The Na deposit distribution changes from nonparametric distribution to normal distribution which can be attributed to the effect of interparticle diffusion coupling (IDP). The atomic information on the Na deposit was revealed via cryogenic transmission electron microscopy.

Zn Electrodeposition by an In Situ Electrochemical Liquid Phase Transmission Electron Microscope.

Alternative battery technologies are required to meet growing energy demands and to solve the limitations of the present energy technologies. As such, it is necessary to look beyond lithium-ion batteries. Zinc batteries enable high power density while being sourced from abundant and cost-effective materials. In this paper, the effect of the applied current and electrolyte flow rate on the early stage of Zn dendrite formation was characterized by in situ electrochemical liquid phase transmission electron microscopy (EC-LPTEM). For the first time, the square root relation is revealed between time and Zn dendrite growth on the lateral direction, indicating a diffusion-limited growth. It is intriguing that a higher applied current leads to longer incubation time. In situ EC-LPTEM can provide a useful strategy for understanding characteristics of unstable dendritic growth. The finding can help rationalize the electrode engineering design and parameters selection to avoid dendrite formation.

Stable Interfaces in a Sodium Metal-Free, Solid-State Sodium-Ion Battery with Gradient Composite Electrolyte.

Composite electrolytes (CE) combining a ceramic filler and a polymer matrix is an effective way to enhance battery safety. But the increased ceramic filler mass fraction decreases the flexibility, which increases the interfacial resistance. To alleviate interfacial resistance further, a gradient composite electrolyte (GCE) using a Sc, Ge-doped Na3Zr2Si2PO12 (NZSP) as the ceramic filler and poly(ethylene oxide) (PEO) as the polymer matrix is proposed. The outer layer contains a low concentration of ceramic filler to improve interfacial contact, and the central layer contains a high concentration of ceramic filler to inhibit dendrite penetration. This GCE possesses an enhanced conductivity (4.0 × 10-5 S cm-1 at 30 °C) and a reduced interfacial resistance. Furthermore, the safety was boosted using Sn4P3@CNT/C as the high-capacity anode active material and Na3V2(PO4)3 (NVP) as the cathode active material. This ultrasafe sodium metal-free, solid-state sodium-ion battery (SSSIB) displays an impressive cycling performance.

ZIF-8 derived hollow carbon to trap polysulfides for high performance lithium-sulfur batteries.

Lithium-sulfur batteries (LSBs) have a high theoretical energy density and are low cost. However, the undesirable shuttle effect with the solid discharge product, Li2S, greatly impedes their market penetration. Conductive carbon materials with functional elements are beneficial in controlling the shuttle effect and can reactivate the Li2S, leading to improved long term cycling performance of LSBs. Herein, we report zinc (Zn) and nitrogen (N) co-doped ZIF-8 derived hollow carbon (ZHC) as a promising separator coating for LSBs to control the shuttle effect. The hollow area in the ZHC is identified to be around 250 nm with a carbonized outer surface thickness of approximately 50 nm. The presence of Zn and N in the nanohollow carbon structure helps to mitigate polysulfide (PS) diffusion in LSBs. Furthermore, the hollow interior of the carbon acts as a PS pocket to physically capture the PS and in addition Zn and N chemically attract the PS through polar-polar and metal sulfide interactions. The ZHC with its unique architecture and functional groups shows a promising performance with an initial specific capacity (S.cap) of 842 mA h g-1 at 4.80 mg cm-2 and cycling stability until 400 cycles, which is considerably higher in comparison with the cycling performance of parent ZIF-8.

Biomimetic Sn4P3 Anchored on Carbon Nanotubes as an Anode for High-Performance Sodium-Ion Batteries.

Recently, Sn4P3 has emerged as a promising anode for sodium-ion batteries (SIBs) due to the high specific capacity. However, the use of Sn4P3 has been impeded by capacity fade and an inferior rate performance. Herein, a biomimetic heterostructure is reported by using a simple hydrothermal reaction followed by thermal treatment. This bottlebrush-like structure consists of a stem-like carbon nanotube (CNT) as the electron expressway and mechanical support; fructus-like Sn4P3 nanoparticles as the active material; and the permeable stoma-like thin carbon coating as the buffer layer. Having benefited from the biomimetic structure, a superior electrochemical performance is obtained in the SIBs. It exhibits a high capacity of 742 mA h g-1 after 150 cycles at 0.2C, and superior rate performance with 449 mA h g-1 at 2C after 500 cycles. Moreover, the sodium storage mechanism is confirmed by cyclic voltammetry and ex situ X-ray diffraction and transmission electron microscopy. In situ electrochemical impedance spectroscopy was adopted to analyze the reaction dynamics. This research represents a further step toward figuring out the inferior electrochemical performance of other metal phosphide materials.

Catalyst-Electrolyte Interactions in Aqueous Reline Solutions for Highly Selective Electrochemical CO2 Reduction.

Invited for this month's cover is the group of Tom Rufford at the University of Queensland. The image shows how choline chloride and urea in a reline solution interact with the surface of a silver cathode to enhance the selectivity of electrochemical CO2 reduction to CO. The Full Paper itself is available at 10.1002/cssc.201902433.

Catalyst-Electrolyte Interactions in Aqueous Reline Solutions for Highly Selective Electrochemical CO2 Reduction.

Achieving high product selectivities is one challenge that limits viability of electrochemical CO2 reduction (CO2 R) to chemical feedstocks. Here, it was demonstrated how interactions between Ag foil cathodes and reline (choline chloride + urea) led to highly selective CO2 R to CO with a faradaic efficiency of (96±8) % in 50 wt % aqueous reline at -0.884 V vs. the reversible hydrogen electrode (RHE), which is a 1.5-fold improvement over CO2 R in KHCO3 . In reline the Ag foil was roughened by (i) dissolution of oxide layers followed by (ii) electrodeposition of Ag nanoparticles back on cathode. This surface restructuring exposed low-coordinated Ag atoms, and subsequent adsorption of choline ions and urea at the catalyst surface limited proton availability in the double layer and stabilized key intermediates such as *COOH. These approaches could potentially be extended to other electrocatalytic metals and lower-viscosity deep eutectic solvents to achieve higher-current-density CO2 R in continuous-flow cell electrolyzers.

Multifunctional Effects of Sulfonyl-Anchored, Dual-Doped Multilayered Graphene for High Areal Capacity Lithium Sulfur Batteries.

Li-S batteries (LSBs) require a minimum 6 mAh cm-2 areal capacity to compete with the state-of-the-art lithium ion batteries (LIBs). However, this areal capacity is difficult to achieve due to a major technical issue-the shuttle effect. Nonpolar carbon materials limit the shuttle effect through physical confinement. However, the polar polysulfides (PSs) only provide weak intermolecular interactions (0.1-0.7 eV) with these nonpolar carbon materials. The physically encapsulated PSs inside the nonpolar carbon scaffold eventually diffuses out and starts shuttling. Chemically interactive hosts are more effective at interacting with the PSs due to high binding energies. Herein, a multifunctional separator coating of nitrogen-doped multilayer graphene (NGN) and -SO3 - containing Nafion (N-NGN) is used to mitigate PS shuttling and to produce a high areal capacity LSB. The Nafion is used as a binder instead of PVDF to provide an additional advantage of -SO3 - to chemically bind the PS. The motive of this research is to investigate the effect of highly electronegative N and -SO3 - (N-NGN) in comparison with the -OH, -COOH, and -SO3 - groups from a hydroxyl graphene and Nafion composite (N-OHGN) to mitigate PS shuttling in LSBs. The highly conductive doped graphene architecture (N-NGN) provides efficient pathways for both electrons and ions, which accelerates the electrochemical conversion at high sulfur loading. Moreover, the electron-rich pyridine N and -SO3 - show strong chemical affinity with the PS through polar-polar interactions, which is proven by the superior electrochemical performance and density functional theory calculations. Further, the N-NGN (5 h) produces a maximum areal capacity of 12.0 and 11.0 mAh cm-2, respectively, at 15 and 12 mg cm-2 sulfur loading. This areal capacity limit is significantly higher than the required areal capacity of LSBs for commercial application, which shows the significant strength of N-NGN as an excellent separator coating for LSBs.

Enhancing Oxygen Reduction Reaction Activity and CO2 Tolerance of Cathode for Low-Temperature Solid Oxide Fuel Cells by in Situ Formation of Carbonates.

Development of low-cost and cobalt-free efficient cathode materials for oxygen reduction reaction (ORR) remains one of the paramount motivations for material researchers at a low temperature (<650 °C). In particular, iron-based perovskite oxides show promise as electrocatalysts for ORR because Fe metal is cheaper and naturally abundant, exhibit matched thermal expansion with contacting components such as electrolytes, and show high tolerance in a CO2-containing atmosphere. Herein, we demonstrated a new mechanism, the in situ formation of alkali metal carbonates at the cathode surface. This new mechanism leads to an efficient and robust cobalt-free electrocatalyst (Sr0.95A0.05Fe0.8Nb0.1Ta0.1O3-δ, SAFNT5, A = Li, Na, and K) for the application of low-temperature solid oxide fuel cells (LT-SOFCs). Our results revealed that the formation of Li\K carbonates boosts the ORR activity with an area-specific resistance as low as 0.12 and 0.18 Ω cm2 at 600 °C, which show the highest performance of the cobalt-free single-phase cathode that has been ever reported so far. We also find that the chemical stability and tolerance of tested cathodes toward CO2 poisoning significantly improved with alkali carbonates, as compared to the pristine SrFe0.8Nb0.1Ta0.1O3-δ (SFNT) at 600 °C. This work demonstrates the conclusive role of alkali carbonates in developing highly efficient and stable cobalt-free cathodes for LT-SOFCs and CO2 neutralization.

Porous Scandia-Stabilized Zirconia Layer for Enhanced Performance of Reversible Solid Oxide Cells.

Reversible solid oxide cells (RSOCs) developed so far display short-term stability during solid oxide electrolysis cell (SOEC) mode. This is due to the delamination of the strontium-doped lanthanum manganite (LSM) air electrode when tested for a long time. Here, we report a highly stable RSOC operation of LSM for 5 cycles using half and full cells. A scandia-stabilized zirconia (SSZ) porous layer was applied between the dense SSZ electrolyte and the porous LSM electrode. The half-cells were tested under ±0.5 A cm-2, whereas the full cells were tested at +0.5 and -0.25 A cm-2 at 800 °C. It was found that the cells with a porous SSZ layer are stable and show a performance increase after five RSOC cycles. The ohmic and polarization resistance of both the half and full cells decreased after each cycle. Also, the maximum power density of the full cell increased from 425 to 550 mW cm-2, whereas the electrolysis current density increased from 294 to 407 mA cm-2 after 5 cycles at 1.3 V in 10% H2O/90% H2, at 800 °C. This performance enhancement can be ascribed to the creation of oxygen vacancies in LSM under applied current, the alleviation of oxygen partial pressure from the interface and the introduction of electronic conductivity in the electrolyte near the interface. The cell without the SSZ porous layer experienced the zirconate formation, high oxygen partial pressure at the interface as well as the silver deposition at the electrode-electrolyte interface. Therefore, an increase in the polarization resistance for the half-cell and a decrease in the electrolysis current density for the full cell were observed.

Recent Progress on Advanced Materials for Solid-Oxide Fuel Cells Operating Below 500 °C.

Solid-oxide fuel cells (SOFCs) are electricity generators that can convert the chemical energy in various fuels directly to the electric power with high efficiency. Recent advances in materials and related key components for SOFCs operating at ≈500 °C are summarized here, with a focus on the materials, structures, and techniques development for low-temperature SOFCs, including the analysis of most of the critical parameters affecting the electrochemical performance of the electrolyte, anode, and cathode. New strategies, such as thin-film deposition, exsolution of nanoparticles from perovskites, microwave plasma heating, and finger-like channeled electrodes, are discussed. These recent developments highlight the need for electrodes with higher activity and electrolytes with greater conductivity to generate a high electrochemical performance at lower temperatures.

New composites of nanoparticle Cu (I) oxide and titania in a novel inorganic polymer (geopolymer) matrix for destruction of dyes and hazardous organic pollutants.

New photoactive composites to efficiently remove organic dyes from water are reported. These consist of Cu2O/TiO2 nanoparticles in a novel inorganic geopolymer matrix modified by a large tertiary ammonium species (cetyltrimethylammonium bromide, CTAB) whose presence in the matrix is demonstrated by FTIR spectroscopy. The CTAB does not disrupt the tetrahedral geopolymer structural silica and alumina units as demonstrated by (29)Si and (27)Al MAS NMR spectroscopy. SEM/EDS, TEM and BET measurements suggest that the Cu2O/TiO2 nanoparticles are homogenously distributed on the surface and within the geopolymer pores. The mechanism of removal of methylene blue (MB) dye from solution consists of a combination of adsorption (under dark conditions) and photodegradation (under UV radiation). MB adsorption in the dark follows pseudo second-order kinetics and is described by Freundlich-Langmuir type isotherms. The performance of the CTAB-modified geopolymer based composites is superior to composites based on unmodified geopolymer hosts, the most effective composite containing 5wt% Cu2O/TiO2 in a CTAB-modified geopolymer host. These composites constitute a new class of materials with excellent potential in environmental protection applications.