Cubic MnS-FeS2 Composites Derived from a Prussian Blue Analogue as Anode Materials for Sodium-Ion Batteries with Long-Term Cycle Stability

Cubic N,S codoped carbon coating MnS-FeS₂ composites (MnS-FeS₂@NSC) with a hollow structure were prepared and used as anode materials for sodium-ion batteries. MnS-FeS₂@NSC exhibits excellent cycle performance and high rate capability and delivered a reversible capacity of 501.0 mAh g^-1 after 800 cycles at a current density of 0.1 A g^-1 with a capacity retention of 81%. More importantly, the MnS-FeS₂@NSC anode holds long-term cycle stability; the capacity can remain 134.0 mAh g^-1 after 14 500 cycles at 4 A g^-1. Kinetic analysis demonstrated that Na⁺ storage follows a pseudocapacitive dominating process, which is ascribed to the origin of the outstanding rate performance of the MnS-FeS₂@NSC material. The enhancement of electrochemical performance is attributed to the hollow structure and the N,S codoped carbon coating structure, which can reduce the diffusion distance for sodium ions and electrons, alleviate volume expansion during sodium-ion insertion/extraction, and retain the structural integrity effectively. Furthermore, a two-step sodiation processes with FeS₂ sodiation prior to MnS was demonstrated by X-ray diffraction (XRD), and the electrochemical impedance spectroscopy (EIS) spectra might indicate that the accumulation of the metallic elements in the preconversion reaction can accelerate the transfer of electrons and ions in the further conversion process.

Novel Approach Through the Harmonized Sulfur in Disordered Carbon Structure for High-Efficiency Sodium-Ion Exchange

Sodium-ion batteries (SiBs) have recently attracted considerable interest due to the plentiful supply of raw materials for their production and their electrochemical behavior, which is similar to that of lithium-ion batteries (LiBs). However, the relatively larger radius of sodium ions than that of lithium ions is not suitable for storage in conventional graphite, which is widely used as the anode. To resolve this issue, in this study, we developed a new harmonized carbon material with a three-dimensional (3D) grapevine-like structure and a sulfur component using an efficient synthesis process. On the basis of these advantages, the harmonized sulfur-carbon material exhibited a highly reversible capacity of 146 mA h g^-1 at an extremely high specific current of 100 A g^-1 and long-term galvanostatic cycling stability at 10 and 100 A g^-1 with superior electrochemical performance. Our results are anticipated to provide new insights into SiB anode materials that would advance their production.

A Scalable Silicon Nanowires-Grown-On-Graphite Composite for High-Energy Lithium Batteries

Silicon (Si) is the most promising anode candidate for the next generation of lithium-ion batteries but difficult to cycle due to its poor electronic conductivity and large volume change during cycling. Nanostructured Si-based materials allow high loading and cycling stability but remain a challenge for process and engineering. We prepare a Si nanowires-grown-on-graphite one-pot composite (Gt-SiNW) via a simple and scalable route. The uniform distribution of SiNW and the graphite flakes alignment prevent electrode pulverization and accommodate volume expansion during cycling, resulting in very low electrode swelling. Our designed nanoarchitecture delivers outstanding electrochemical performance with a capacity retention of 87% after 250 cycles at 2C rate with an industrial electrode density of 1.6 g cm^-3. Full cells with NMC-622 cathode display a capacity retention of 70% over 300 cycles. This work provides insights into the fruitful engineering of active composites at the nano- and microscales to design efficient Si-rich anodes.

Improving the Cycling Stability of Fe3O4/NiO Anode for Lithium Ion Battery by Constructing Novel Bimodal Nanoporous Urchin Network

The development of facile preparation methods and novel three-dimensional structured anodes to improve cycling stability of lithium ion batteries (LIBs) is urgently needed. Herein, a dual-network ferroferric oxide/nickel oxide (Fe3O4/NiO) anode was synthesized through a facile dealloying technology, which is suitable for commercial mass manufacturing. The dual-network with high specific surface area contains a nanoplate array network and a bimodal nanoporous urchin network. It exhibits excellent electrochemical performance as an anode material for LIB, delivering a reversible capacity of 721 mAh g-1 at 100 mA g-1 after 100 cycles. The good lithium storage performance is related to the ample porous structure, which can relieve stress and mitigate the volume change in the charge/discharge process, the interconnected porous network that enhances ionic mobility and permeability, and synergistic effects of two kinds of active materials. The paper provides a new idea for the design and preparation of anode materials with a novel porous structure by a dealloying method and may promote the development of the dealloying field.

Advances in Organic Anode Materials for Na-/K-Ion Rechargeable Batteries

Electrochemical energy storage (EES) devices are gaining ever greater prominence in the quest for global energy security. With increasing applications and widening scope, rechargeable battery technology is gradually finding avenues for more abundant and sustainable systems such as Na-ion (NIB) and K-ion batteries (KIB). Development of suitable electrode materials lies at the core of this transition. Organic redox-active molecules are attractive candidates as negative electrode materials owing to their low redox potentials and the fact that they can be obtained from biomass. Also, the rich structural diversity allows integration into several solid-state polymeric materials. Research in this domain is increasingly focused on deploying molecular engineering to address specific electrochemical limitations that hamper competition with rival materials. This Minireview aims to summarize the advances in both the electrochemical properties and the materials development of organic anode materials.

Simple Approach: Heat Treatment to Improve the Electrochemical Performance of Commonly Used Anode Electrodes for Lithium-Ion Batteries

The lithium-ion battery (LIB) industry has been in high demand for simple and effective methods to improve the electrochemical performance of LIBs. Here, we treated three different widely studied anode electrodes (i.e., Li₄Ti₅O₁₂, TiO₂, and graphite) under vacuum at 250 °C, and compared their electrochemical performance with and without a 250 °C treatment. Without changing the composition of the fabricated electrodes, all of the 250 °C treated electrodes exhibited enhanced specific capacities, and the lithium-ion diffusion was improved in different degrees. By comparing the results of scanning electron microscopy (SEM) and energy-dispersive spectroscopy of the pristine and 250 °C treated electrodes, the 250 °C treatment improved the distribution of a polyvinylidene difluoride (PVDF) binder in the electrodes, resulting in a higher porosity of the 250 °C treated electrodes. The results of X-ray photoelectron spectrometry and SEM of the cycled electrodes confirmed that a uniform distribution of the PVDF binder from the 250 °C treatment played a positive role in the formation of a solid electrolyte interphase layer, thereby delivering higher capacities and capacity retentions than those of electrodes without heat treatment. The simplicity of this modification method provides considerable potential for building high-performance LIBs at a larger scale.

Pomegranate-Like Structured Si@SiOx Composites With High-Capacity for Lithium-Ion Batteries

Silicon anodes with an extremely high theoretical specific capacity of 4,200 mAh g^-1 have been considered as one of the most promising anode materials for next-generation lithium-ion batteries. However, the large volume expansion during lithiation hinders its practical application. In this work, pomegranate-like Si@SiO_x composites were prepared using a simple spray drying process, during which silicon nanoparticles reacted with oxygen and generated SiO_x on the surface. The thickness of the SiO_x layer was tuned by adjusting the drying temperature. In the unique architecture, the SiO_x which serves as the protection layer and the void space in pomegranate-like structure could alleviate the volume expansion during repeated lithium insertion/extraction. As a lithium-ion battery anode, pomegranate-like Si@SiO_x composites dried at 180°C delivered a high specific capacity of 1746.5 mAh g^-1 after 300 cycles at 500 mA g^-1.

Rational Tuning of a Li4SiO4-Based Hybrid Interface with Unique Stepwise Prelithiation for Dendrite-Proof and High-Rate Lithium Anodes

Lithium metal batteries (LMBs) are among the most promising candidates for high energy-density batteries. However, dendrite growth constitutes the biggest stumbling block to its development. Herein, Li₄SiO₄-dominating organic-inorganic hybrid layers are rationally designed by SiO₂ surface modification and the stepwise prelithiation process. SiO₂ nanoparticles construct a zigzagged porous structure, where a solid electrolyte interface (SEI) has grown and penetrated to form a conformal and compact hybrid surface. Such a first-of-this-kind structure enables enhanced Li dendrite prohibition and surface stability. The interfacial chemistry reveals a two-step prelithiation process that transfers SiO₂ into well-defined Li₄SiO₄, the components of which exhibits the lowest diffusion barrier (0.12 eV atom^-1) among other highlighted SEI species, such as LiF (0.175 eV atom^-1) for the current artificial layer. Therefore, the decorated Li allows for an improved high-rate full-cell performance (LiFePO₄/modified Li) with a much higher capacity of 65.7 mAh g^-1 at 5C (1C = 170 mAh g^-1) than its counterpart with bare Li (∼3 mAh g^-1). Such a protocol provides insights into the surface architecture and SEI component optimization through prelithiation in the target of stable, dendrite-proof, homogenized Li⁺ solid-state migration and high electrochemical performance for LMBs.

Novel Hoberman Sphere Design for Interlaced Mn3O4@CNT Architecture with Atomic Layer Deposition-Coated TiO2 Overlayer as Advanced Anodes in Li-Ion Battery

The Hoberman sphere is a stable and stretchable spatial structure with a unique design concept, which can be taken as the ideal prototype of the internal mechanical/conductive skeleton for the anode with large volume change. Herein, Mn₃O₄ nanoparticles are interlaced with a Hoberman sphere-like interconnected carbon nanotube (CNT) network via a facile self-assembly strategy in which Mn₃O₄ can "locally expand" in the CNT network, limit the volume expansion to the interior space, and maintain a stable outer surface of the hybrid particle. Furthermore, an ultrathin uniform ALD-coated TiO₂ shell is adopted to stabilize the solid electrolyte interphase (SEI), provide high electron conductivity and lithium ion (Li⁺) diffusivity with lithiated Li_xTiO₂, and enhance the reaction kinetics of the Mn₃O₄ by an "electron-density enhancement effect". With this design, the Mn₃O₄@CNT/TiO₂ exhibits a high capacity of 1064 mAh g^-1 at 0.1 A g^-1, a stable cycling stability over 200 cycles, a superior rate capability, and a commercial-level areal capacity of 4.9 mAh cm^-2. In this way, a novel electrode design strategy is achieved by the Hoberman sphere-like CNT design along with the in situ porous formation, which can not only achieve a high-performance anode for LIBs but also can be widely adapted in a variety of advanced electrode materials for alkali metal ion batteries.

Okra-Like Fe7 S8 /C@ZnS/N-C@C with Core-Double-Shelled Structures as Robust and High-Rate Sodium Anode

Core-multishelled structures with controlled chemical composition have attracted great interest due to their fascinating electrochemical performance. Herein, a metal-organic framework (MOF)-on-MOF self-templated strategy is used to fabricate okra-like bimetal sulfide (Fe₇ S₈ /C@ZnS/N-C@C) with core-double-shelled structure, in which Fe₇ S₈ /C is distributed in the cores, and ZnS is embedded in one of the layers. The MOF-on-MOF precursor with an MIL-53 core, a ZIF-8 shell, and a resorcinol-formaldehyde (RF) layer (MIL-53@ZIF-8@RF) is prepared through a layer-by-layer assembly method. After calcination with sulfur powder, the resultant structure has a hierarchical carbon matrix, abundant internal interface, and tiered active material distribution. It provides fast sodium-ion reaction kinetics, a superior pseudocapacitance contribution, good resistance of volume changes, and stepwise sodiation/desodiation reaction mechanism. As an anode material for sodium-ion batteries, the electrochemical performance of Fe₇ S₈ /C@ZnS/N-C@C is superior to that of Fe₇ S₈ /C@ZnS/N-C, Fe₇ S₈ /C, or ZnS/N-C. It delivers a high and stable capacity of 364.7 mAh g^-1 at current density of 5.0 A g^-1 with 10 000 cycles, and registers only 0.00135% capacity decay per cycle. This MOF-on-MOF self-templated strategy may provide a method to construct core-multishelled structures with controlled component distributions for the energy conversion and storage.

Boosting Transport Kinetics of Cobalt Sulfides Yolk-Shell Spheres by Anion Doping for Advanced Lithium and Sodium Storage

Cobalt sulfides have been popularly used in energy storage because of their high theoretical capacity and abundant redox reactions. However, poor reaction kinetics, rapid capacity decay, and severe polarization owing to volume changes during electrochemical reaction are still huge challenges for cobalt sulfides in practical applications. Herein, cobalt sulfide yolk-shell spheres were synthesized by phosphorus doping (P-CoS) to stabilize the structure of cobalt sulfides and improve their electronic/ion conductivity. Kinetic tests and density functional theory calculations confirm that the introduction of phosphorus into cobalt sulfides greatly reduces the diffusion barrier of Li⁺ in the intrinsic structure, thereby improving the reaction kinetics of electrode materials during the Li⁺ insertion/extraction process. In consequence, the P-CoS electrode delivers a high lithium storage capacity (781 mAh g^-1 after 100 cycles at 0.2 A g^-1 ), excellent rate capability (489 mAh g^-1 at 10 A g^-1 ), and outstanding cycling stability (no significant capacity decay over 4000 cycles at 5 A g^-1 ). Especially for sodium-ion battery application, the P-CoS electrode expresses a striking capacity of approximately 260 mAh g^-1 at 2 A g^-1 after 900 cycles.

Enhancing the Cycling Stability by Tuning the Chemical Bonding between Phosphorus and Carbon Nanotubes for Potassium-Ion Battery Anodes

Phosphorus/carbon (P/C) composites as promising potassium-ion storage materials have been extensively investigated for its compound superiorities of high specific capacity and favorable electronic conductivity. However, the effects of different chemical bonding states between P and the carbon matrix for potassium-ion storage and cycling performance still need to be investigated. Herein, three P/C composites with different chemical bonding states were successfully fabricated through simply ball-milling red P with carboxylic group carbon nanotubes (CGCNTs), carbon nanotubes (CNTs), and reduced carboxylic group carbon nanotubes (RCGCNTs), respectively. When used as potassium-ion battery (PIB) anodes, the red P and CGCNT (P-CGCNT) composite deliver the most outstanding cycling stability (402.6 mAh g^-1 over 110 cycles) with a favorable capacity retention of 68.26% at a current density of 0.1 A g^-1, much higher than that of the phosphorus-CNT (P-CNT) composite (297.5 mAh g^-1 and 50.40%). Based on the results of X-ray photoelectron spectroscopy and electrochemical performance, we propose that the existence of a carboxyl functional group will be instrumental for the formation of the P-O-C bond. More importantly, when compared with the P-C bond, the P-O-C bond can lead to a higher reversible capacity and a better long-term cycling stability as a result of the more robust bonding energy of the P-O-C bond (585 KJ mol^-1) than that of the P-C bond (264 kJ mol^-1). This work provides some insights into designing high-performance P anodes for PIBs.

Electrochemical C-H Functionalization of (Hetero)Arenes-Optimized by DoE

A novel approach towards the activation of different arenes and purines including caffeine and theophylline is presented. The simple, safe and scalable electrochemical synthesis of 1,1,1,3,3,3‐hexafluoroisopropanol (HFIP) aryl ethers was conducted using an easy electrolysis setup with boron‐doped diamond (BDD) electrodes. Good yields up to 59 % were achieved. Triethylamine was used as a base as it forms a highly conductive media with HFIP, making additional supporting electrolytes superfluous. The synthesis was optimized using Design of Experiment (DoE) techniques giving a detailed insight to the significance of the reaction parameters. The mechanism was investigated by cyclic voltammetry (CV). Subsequent transition metal‐catalyzed as well as metal‐free functionalization led to interesting motifs in excellent yields up to 94 %.

Construction of Multifunctional Nanoarchitectures in One Step on a Composite Fuel Catalyst through In Situ Exsolution of La0.5Sr0.5Fe0.8Ni0.1Nb0.1O3-δ

Multifunctional nanoarchitecture (MNA) on catalysts has attracted great attention because of its capability to improve the performance, durability, and resistance to unwanted side reactions. Such structures, however, are conventionally prepared by deposition methods, which inherently suffer from costly and time-consuming drawbacks. Here, we report a simple one-step process to successfully construct a novel MNA with core-shell nanoparticles anchored at the heterointerface of dual-phase oxide substrates through a phase transition and in situ exsolution of perovskite La_0.5Sr_0.5Fe_0.8Ni_0.1Nb_0.1O_3-δ (LSFNNb0.1) in wet H₂ (3% H₂O) at 800 °C. The core-shell nanoparticles are composed of a Ni-Fe alloy core and a SrLaFeO₄-type layered perovskite oxide shell (RP-Ruddlesden-Popper-layered perovskites), which synergistically improves the electrochemical activity and effectively suppresses aggregation and coarsening of the metallic core. The RP phase also covers the surface of perovskite bulk (SP-single perovskite), forming the heterointerface and preventing further decomposition of the SP phase. The RP/SP heterointerface may improve the kinetics of surface exchange of oxygen species, resulting in the enhancement of performance and durability of the reduced LSFNNb0.1 as an anode for solid oxide fuel cells (SOFCs). A doped zirconia electrolyte-supported single cell with the anode achieves the maximum power density (MPD) of 0.83 W cm^-2 at 800 °C in wet H₂, and the corresponding polarization resistance is as low as 0.15 Ω cm². This work reveals the formation mechanism of the MNA by investigating the evolution of the crystal structure, composition and morphology of LSFNNb0.1, when changing reducing temperature and time in wet H₂ and 5% H₂-Ar. The oxygen vacancies and phase transitions are found to play important roles in the formation of the MNA. The construction of MNAs in one step opens a new opportunity to design and prepare high-performance and stable catalysts for applications in energy conversion and storage.

Facile Green Synthesis of Pseudocapacitance-Contributed Ultrahigh Capacity Fe2(MoO4)3 as an Anode for Lithium-Ion Batteries

The investigation into the use of earth-abundant elements as electrode materials for lithium-ion batteries (LIBs) is becoming more urgent because of the high demand for electric vehicles and portable devices. Herein, a new green synthesis strategy, based on a facile solid-state reaction with the assistance of water droplets' vapor, was conducted to prepare Fe₂(MoO₄)₃ nanosheets as anode materials for LIBs. The obtained sample possesses a two-dimensional stacked nanosheet construction with open gaps providing a much higher surface area compared to the bulk sample conventionally synthesized. The nanosheet sample delivers an ultrahigh reversible capacity (1983.6 mA h g^-1) at a current density of 100 mA g^-1 after 400 cycles, which could be related to the contribution of pseudocapacitance. The enhancement in cyclability and rated performance with an interesting increased capacity could be caused by the effect of electrochemical milling and the in situ formation of metallic particles in its lithium-ion storage mechanism.

State-of-the-Art Electrode Materials for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) were investigated as recently as in the seventies. However, they have been overshadowed for decades, due to the success of lithium-ion batteries that demonstrated higher energy densities and longer cycle lives. Since then, the witness a re-emergence of the SIBs and renewed interest evidenced by an exponential increase of the publications devoted to them (about 9000 publications in 2019, more than 6000 in the first six months this year). This huge effort in research has led and is leading to an important and constant progress in the performance of the SIBs, which have conquered an industrial market and are now commercialized. This progress concerns all the elements of the batteries. We have already recently reviewed the salts and electrolytes, including solid electrolytes to build all-solid-state SIBs. The present review is then devoted to the electrode materials. For anodes, they include carbons, metal chalcogenide-based materials, intercalation-based and conversion reaction compounds (transition metal oxides and sulfides), intermetallic compounds serving as functional alloying elements. For cathodes, layered oxide materials, polyionic compounds, sulfates, pyrophosphates and Prussian blue analogs are reviewed. The electrode structuring is also discussed, as it impacts, importantly, the electrochemical performance. Attention is focused on the progress made in the last five years to report the state-of-the-art in the performance of the SIBs and justify the efforts of research.

Synthesis and Characterization of Li-C Nanocomposite for Easy and Safe Handling

Metallic lithium (Li) anode batteries have attracted considerable attention due to their high energy density value. However, metallic Li is highly reactive and flammable, which makes Li anode batteries difficult to develop. In this work, for the first time, we report the synthesis of metallic Li-embedded carbon nanocomposites for easy and safe handling by a scalable ion beam-based method. We found that vertically standing conical Li-C nanocomposite (Li-C NC), sometimes with a nanofiber on top, can be grown on a graphite foil commonly used for the anodes of lithium-ion batteries. Metallic Li embedded inside the carbon matrix was found to be highly stable under ambient conditions, making transmission electron microscopy (TEM) characterization possible without any sophisticated inert gas-based sample fabrication apparatus. The developed ion beam-based fabrication technique was also extendable to the synthesis of stable Li-C NC films under ambient conditions. In fact, no significant loss of crystallinity or change in morphology of the Li-C film was observed when subjected to heating at 300 °C for 10 min. Thus, these ion-induced Li-C nanocomposites are concluded to be interesting as electrode materials for future Li-air batteries.

Durian-Inspired Design of Bismuth-Antimony Alloy Arrays for Robust Sodium Storage

Sodium-ion batteries have attracted widespread attention for cost-effective and large-scale electric energy storage. However, their practical deployment has been largely retarded by the lack of choice of efficient anode materials featuring large capacity and electrochemical stability and robustness. Herein, we report a durian-inspired design and template-free fabrication of a robust sodium anode based on triangular pyramid arrays of Bi_0.75Sb_0.25 alloy electrodeposited on Cu substrates. The Bi_0.75Sb_0.25 arrays exhibit an appreciable electrochemical robustness for sodium storage, sustaining a reversible capability 335 mAh g^-1 at a high rate of 2.5 A g^-1 and 87% of the initial capacity over 2000 cycles. We further demonstrate the applicability of the Bi_0.75Sb_0.25 array anode in sodium full cells by pairing it with a Na₃V₂(PO₄)₃/C cathode. This full cell achieves a high specific energy of 203 Wh kg^-1 (based on both active electrodes). Such an enhanced performance is attributed to the thorny-durian-like architecture and bimetallic alloy composition. The pyramid tip induces ion enrichment for rapid charge-transfer reaction, while the alloy design reduces the electrode volume swelling for stable Na cycling.

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.

Lanthanum Ferrites-Based Exsolved Perovskites as Fuel-Flexible Anode for Solid Oxide Fuel Cells

Exsolved perovskites can be obtained from lanthanum ferrites, such as La_0.6Sr_0.4Fe_0.8Co_0.2O₃, as result of Ni doping and thermal treatments. Ni can be simply added to the perovskite by an incipient wetness method. Thermal treatments that favor the exsolution process include calcination in air (e.g., 500 °C) and subsequent reduction in diluted H₂ at 800 °C. These processes allow producing a two-phase material consisting of a Ruddlesden–Popper-type structure and a solid oxide solution e.g., α-Fe_100-y-zCo_yNi_zO_x oxide. The formed electrocatalyst shows sufficient electronic conductivity under reducing environment at the Solid Oxide Fuel Cell (SOFC) anode. Outstanding catalytic properties are observed for the direct oxidation of dry fuels in SOFCs, including H₂, methane, syngas, methanol, glycerol, and propane. This anode electrocatalyst can be combined with a full density electrolyte based on Gadolinia-doped ceria or with La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ (LSGM) or BaCe_0.9Y_0.1O_3-δ (BYCO) to form a complete perovskite structure-based cell. Moreover, the exsolved perovskite can be used as a coating layer or catalytic pre-layer of a conventional Ni-YSZ anode. Beside the excellent catalytic activity, this material also shows proper durability and tolerance to sulfur poisoning. Research challenges and future directions are discussed. A new approach combining an exsolved perovskite and an NiCu alloy to further enhance the fuel flexibility of the composite catalyst is also considered. In this review, the preparation methods, physicochemical characteristics, and surface properties of exsoluted fine nanoparticles encapsulated on the metal-depleted perovskite, electrochemical properties for the direct oxidation of dry fuels, and related electrooxidation mechanisms are examined and discussed.

Honeycombed Porous, Size-Matching Architecture for High-Performance Hybrid Direct Carbon Fuel Cell Anode

Direct carbon fuel cells (DCFCs) demonstrate both superior electrical efficiency and fuel utilization compared to all other types of fuel cells, and it will be the most promising carbon utilization technology if the sluggish anode reaction kinetics that derives from the use of solid fuel can be addressed. Herein, the electrode morphology and fuel particle size are comprehensively considered to fabricate an efficient DCFC anode skeleton. A honeycombed and size-matching anode architecture with dual-scale porous structure is developed by water droplet templating, which demonstrates an efficient strategy to address the challenge of poor carbon reactivity and improve the electrochemical performance of DCFCs. Single cell with this designed anode framework demonstrates excellent performance, and the maximum power density is as high as 765 mW cm^-2 at 800 °C when using the matching carbon fuel. The size-matching between carbon fuel and anode framework shows a remarkable effect on the improvement of mass-transfer processes at the anodes. The significant contribution of the difficult electrochemical oxidation of carbon to the output performance is also demonstrated. These results represent a promising structural design strategy in developing high-performing fuel cells.

Three-Dimensional Topotactic Host Structure-Secured Ultrastable VP-CNO Composite Anodes for Long Lifespan Lithium- and Sodium-Ion Capacitors

Performance degradation of lithium/sodium-ion capacitors (LICs/SICs) mainly originates from anode pulverization, particularly the alloying and conversion types, and has spurred research for alternatives with an insertion mechanism. Three-dimensional (3D) topotactic host materials remain much unexplored compared to two-dimensional (2D) ones (graphite, etc.). Herein, vanadium monophosphide (VP) is designed as a 3D topotactic host anode. Ex situ electrochemical characterizations reveal that there are no phase changes during (de)intercalation, which follows the topotactic intercalation mechanism. Computational simulations also confirm the metallic feature and topotactic structure of VP with a spacious interstitial position for the accommodation of guest species. To boost the electrochemical performance, carbon nano-onions (CNOs) are coupled with 3D VP. Superior specific capacity and rate capability of VP-CNOs vs lithium/sodium can be delivered due to the fast ion diffusion nature. An exceptional capacity retention of above 86% is maintained after 20 000 cycles, benefitting from the topotactic intercalation process. The optimized LICs/SICs exhibit high energy/power densities and an ultrastable lifespan of 20 000 cycles, which outperform most of the state-of-the-art LICs and SICs, demonstrating the potential of VP-CNOs as insertion anodes. This exploration would draw attention with regard to insertion anodes with 3D topotactic host topology and provide new insights into anode selection for LICs/SICs.

Cl- Doping Strategy to Boost the Lithium Storage Performance of Lithium Titanium Phosphate

Because of energy storage limitations and the high demand for energy, aqueous rechargeable lithium batteries (ARLBs) are receiving widespread attention due to their excellent performance and high safety. Lithium titanium phosphate (LiTi₂(PO₄)₃) exhibits the potential to serve as anodes for ARLBs because it has a three-dimensional channel and a stable structure. We employed an anion (Cl⁻) doping strategy to boost the lithium storage performance of LiTi₂(PO₄)₃. A series of LiTi₂(PO₄)₃/C composites doped with Cl⁻ on PO43- were successfully synthesized with a sol-gel technique as anodes for ARLBs. The effects of chlorine doping with different content on the properties of LiTi₂(PO₄)_3−xCl_3x/C (x = 0.05, 0.10, and 0.15) were investigated systematically. The doping of chlorine in appropriate amounts did not significantly impact the main structure and morphology of LiTi₂(PO₄)₃/C. However, chlorine doping greatly increased the performance of LiTi₂(PO₄)₃/C. LiTi₂(PO₄)_2.9Cl_0.3/C (LCl-10) showed the best electrochemical properties. It delivered a discharge capacity of 108.5 and 85.5 mAh g⁻¹ at 0.5 and 15°C, respectively, with an increase of 13.2 and 43.3 mAh g⁻¹ compared to blank LiTi₂(PO₄)₃ (LCl). In addition, the discharge capacity of LCl-10 was maintained at 61.3% after 1,000 cycles at 5°C, implying an apparent improvement compared to LCl (35.3%). Our study showed that a chlorine-doped LiTi₂(PO₄)₃/C composite is a potential anode for high-performance ARLBs.

Europium-Doped Ceria Nanowires as Anode for Solid Oxide Fuel Cells

CeO₂-based materials have been studied intensively as anodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). In this work, pristine and europium (Eu)-doped CeO₂ nanowires were comprehensively investigated as anode materials for IT-SOFCs, by a combination of theoretical predictions and experimental characterizations. The results demonstrate: (1) Oxygen vacancies can be energetically favorably introduced into the CeO₂ lattice by Eu doping; (2) The lattice parameter of the ceria increases linearly with the Eu content when it varies from 0 to 35 mol.%, simultaneously resulting in a significant increase in oxygen vacancies. The concentration of oxygen vacancies reaches its maximum at a ca. 10 mol.% Eu doping level and decreases thereafter; (3) The highest oxygen ion conductivity is achieved at a Eu content of 15 mol.%; while the 10 mol.% Eu-doped CeO₂ sample displays the highest catalytic activity for H₂-TPR and CO oxidization reactions. The conducting and catalytic properties benefit from the expanded lattice, the large amount of oxygen vacancies, the enhanced reactivity of surface oxygen and the promoted mobility of bulk oxygen ions. These results provide an avenue toward designing and optimizing CeO₂ as a promising anode for SOFCs.

Sulfur-Mediated Interface Engineering Enables Fast SnS Nanosheet Anodes for Advanced Lithium/Sodium-Ion Batteries

Interface design is generally helpful to ameliorate the electrochemical properties of electrode materials but challenging as well. Herein, in situ sulfur-mediated interface engineering is developed to effectively raise the kinetics properties of the SnS nanosheet anodes, which is realized by a synchronous reduction and carbon deposition/doping process. The sulfur in the raw SnS₂ directly induces the sulfur-doped amorphous carbon layer onto the in situ reduced SnS nanosheet. In situ and ex situ electrochemical characterizations suggest that the sulfur-mediated interface layer can enhance the reversibility and kinetics properties, promote the ion/electron swift delivery, and maintain the configurational wholeness of the SnS nanosheet anodes. Consequently, a relatively high Li-storage capacity of 922 mAh g^-1 and Na-storage capacity of 349 mAh g^-1 at 1.0 A g^-1 even after 1000 and 300 long-term cycles are achieved, respectively. The facile method and excellent performance suggest the effective interface tuning for developing the SnS-based anodes for batteries and beyond.