Two-Dimensional Bismuth Oxide Heterostructured Nanosheets for Lithium- and Sodium-Ion Storages

Precision-Grown Bi2O2Se Flakes for Exceptional Electrocatalytic Performance in Acidic Medium

Efficient hydrogen production via electrochemical water splitting is vital for sustainable energy applications, with the HER in acidic media requiring highly effective catalysts. In this study, we report the synthesis of Bi2O2Se nanosheets through a scalable hydrothermal method, achieving exceptional catalytic performance in acidic conditions. The Bi2O2Se nanosheets exhibit a low overpotential of 104 mV at 10 mA cm-2, significantly outperforming other bismuth-based HER catalysts. The superior activity is attributed to the unique structural and electronic properties of Bi2O2Se, which provide abundant active sites and enhance charge transfer efficiency. Electrochemical studies, including Tafel slope analysis and impedance spectroscopy, confirm rapid HER kinetics and reduced charge-transfer resistance. Additionally, the catalysts demonstrate excellent long-term stability under acidic conditions, maintaining their performance during extended electrolysis. This work highlights the potential of Bi2O2Se as a highly efficient and cost-effective catalyst tailored for acidic HER applications. The dual-electrode system comprising Bi2O2Se@CP as the cathode and RuO2@CP as the anode demonstrated outstanding performance in overall water splitting. This system required a battery voltage of only 1.49 V to achieve a current density of 10 mA cm-2, highlighting the superior electrocatalytic efficiency of Bi2O2Se in conjunction with RuO2. By offering valuable insights into the design and optimization of bismuth-based materials, these findings pave the way for advancing sustainable hydrogen production technologies through scalable and efficient catalytic solutions.

Bismuth Oxide Nanoparticle-Enhanced Poly(methyl methacrylate) Composites for I-131 Radiation Shielding: A Combined Simulation and Experimental Investigation

This study investigates the development of advanced radiation shielding materials incorporating bismuth oxide (Bi2O3) nanoparticles (NPs) into polymethyl methacrylate (PMMA) composites, comparing efficacy against I-131 gamma radiation. The NPs exhibit a 1.53-fold reduction in z-average diameter and a significantly higher surface area than Bi2O3, ensuring superior dispersion and structural uniformity within the PMMA matrix. These characteristics, validated through SEM, EDX, and XRD analyses, contribute to enhanced gamma radiation attenuation, leveraging the high atomic number and density of Bi2O3. Mechanical evaluations reveal that increasing Bi2O3-NPs concentrations enhances ductility but reduces tensile strength, likely due to nanoparticle agglomeration and stress concentration. Radiation shielding performance, assessed using XCOM and Phy-X/PSD simulations, demonstrates a direct correlation between Bi2O3 content and attenuation efficiency. Notably, composites with 75% Bi2O3 content exhibit attenuation properties comparable to, or exceeding, those of PbO2, achieving superior shielding efficacy at reduced thicknesses across various photon interaction mechanisms. These findings position Bi2O3 NPs-enhanced PMMA composites as promising lightweight high-performance alternatives to lead-based shields. By addressing toxicity and environmental concerns associated with lead, this work emphasizes the potential of high-Z nanomaterials in advancing radiation protection applications. This study highlights a transformative approach to designing safer and more efficient shielding solutions, contributing to the next generation of radiation protection materials.

Advanced Bismuth-Based Anode Materials for Efficient Potassium Storage: Structural Features, Storage Mechanisms and Modification Strategies

Potassium-ion batteries (PIBs) are considered as a promising energy storage system owing to its abundant potassium resources. As an important part of the battery composition, anode materials play a vital role in the future development of PIBs. Bismuth-based anode materials demonstrate great potential for storing potassium ions (K+) due to their layered structure, high theoretical capacity based on the alloying reaction mechanism, and safe operating voltage. However, the large radius of K+ inevitably induces severe volume expansion in depotassiation/potassiation, and the sluggish kinetics of K+ insertion/extraction limits its further development. Herein, we summarize the strategies used to improve the potassium storage properties of various types of materials and introduce recent advances in the design and fabrication of favorable structural features of bismuth-based materials. Firstly, this review analyzes the structure, working mechanism and advantages and disadvantages of various types of materials for potassium storage. Then, based on this, the manuscript focuses on summarizing modification strategies including structural and morphological design, compositing with other materials, and electrolyte optimization, and elucidating the advantages of various modifications in enhancing the potassium storage performance. Finally, we outline the current challenges of bismuth-based materials in PIBs and put forward some prospects to be verified.

Elf autoencoder for unsupervised exploration of flat-band materials using electronic band structure fingerprints

Two-dimensional materials with flat electronic bands are promising for realising exotic quantum phenomena such as unconventional superconductivity and nontrivial topology. However, exploring their vast chemical space is a significant challenge. Here we introduce elf, an unsupervised convolutional autoencoder that encodes electronic band structure images into fingerprint vectors, enabling the autonomous clustering of materials by electronic properties beyond traditional chemical paradigms. Unsupervised visualisation of the fingerprint space then uncovers hidden chemical trends and identifies promising candidates based on similarities to well-studied exemplars. This approach complements high-throughput ab initio methods by rapidly screening candidates and guiding further investigations into the mechanisms underlying flat-band physics. The elf autoencoder is a powerful tool for autonomous discovery of unexplored flat-band materials, enabling unbiased identification of compounds with desirable electronic properties across the 2D chemical space.

Zn Makes a Difference: Cubic ZnBi38O60 as a Durable and High-Rate Anode for Rechargeable Na-Ion Batteries

A stoichiometric cubic phase of zinc bismuth oxide ZnBi38O60 (ZBO) is introduced as an anode for rechargeable Na-ion batteries. ZBO is synthesized using a coprecipitation method and characterized by various physicochemical techniques. Pristine ZBO shows a high cyclability in an ether-based electrolyte due to the formation of a robust interphase coupled with high Na+ conductivity. Fast charge-transfer kinetics and high chemical compatibility between the electrolyte and electrode result in a high reversible stable capacity of ∼300 mA h/g at 100 mA/g and ∼180 mA h/g at 1000 mA/g for the as-synthesized ZBO. Using in situ diffraction (XRD) experiments, both conversion and alloying reactions are found to be responsible for the observed good performance. A robust, multilayered SEI composed of an inner bismuth-rich inorganic layer and an outer polyether layer with high ionic conductivity is observed using X-ray photoelectron spectroscopy analysis. The battery characteristics are found to be superior to the individual binary oxides, Bi2O3 and ZnO, thus bringing out the advantages of the addition of zinc and the ternary system studied. Preliminary full cell studies with the ZBO anode and Na3V2(PO4)3 cathode show good performance with high energy density and stability. The present investigations reveal a great potential for the anode, ZBO, comprising earth-abundant elements, and will likely lead to an alternate anode material for rechargeable batteries.

Surface Area-Enhanced Cerium and Sulfur-Modified Hierarchical Bismuth Oxide Nanosheets for Electrochemical Carbon Dioxide Reduction to Formate

Electrochemical carbon dioxide reduction reaction (ECO2RR) is a promising approach to synthesize fuels and value-added chemical feedstocks while reducing atmospheric CO2 levels. Here, high surface area cerium and sulfur-doped hierarchical bismuth oxide nanosheets (Ce@S-Bi2O3) are develpoed by a solvothermal method. The resulting Ce@S-Bi2O3 electrocatalyst shows a maximum formate Faradaic efficiency (FE) of 92.5% and a current density of 42.09 mA cm-2 at -1.16 V versus RHE using a traditional H-cell system. Furthermore, using a three-chamber gas diffusion electrode (GDE) reactor, a maximum formate FE of 85% is achieved in a wide range of applied potentials (-0.86 to -1.36 V vs RHE) using Ce@S-Bi2O3. The density functional theory (DFT) results show that doping of Ce and S in Bi2O3 enhances formate production by weakening the OH* and H* species. Moreover, DFT calculations reveal that *OCHO is a dominant pathway on Ce@S-Bi2O3 that leads to efficient formate production. This study opens up new avenues for designing metal and element-doped electrocatalysts to improve the catalytic activity and selectivity for ECO2RR.

(De)sodiation Mechanism of Bi2MoO6 in Na-Ion Batteries Probed by Quasi-Simultaneous Operando PDF and XAS

Operando characterization can reveal degradation processes in battery materials and are essential for the development of battery chemistries. This study reports the first use of quasi-simultaneous operando pair distribution function (PDF) and X-ray absorption spectroscopy (XAS) of a battery cell, providing a detailed, atomic-level understanding of the cycling mechanism of Bi2MoO6 as an anode material for Na-ion batteries. This material cycles via a combined conversion-alloying reaction, where electrochemically active, nanocrystalline Na x Bi particles embedded in an amorphous Na-Mo-O matrix are formed during the first sodiation. The combination of operando PDF and XAS revealed that Bi obtains a positive oxidation state at the end of desodiation, due to formation of Bi-O bonds at the interface between the Bi particles and the Na-Mo-O matrix. In addition, XAS confirmed that Mo has an average oxidation state of +6 throughout the (de)sodiation process and, thus, does not contribute to the capacity. However, the local environment of Mo6+ changes from tetrahedral coordination in the desodiated state to distorted octahedral in the sodiated state. These structural changes are linked to the poor cycling stability of Bi2MoO6, as flexibility of this matrix allows movement and coalescence of the Na x Bi particles, which is detrimental to the electrochemical stability.

Metal Oxide Nanosheet: Synthesis Approaches and Applications in Energy Storage Devices (Batteries, Fuel Cells, and Supercapacitors)

In recent years, the increasing energy requirement and consumption necessitates further improvement in energy storage technologies to obtain high cycling stability, power and energy density, and specific capacitance. Two-dimensional metal oxide nanosheets have gained much interest due to their attractive features, such as composition, tunable structure, and large surface area which make them potential materials for energy storage applications. This review focuses on the establishment of synthesis approaches of metal oxide nanosheets (MO nanosheets) and their advancements over time, as well as their applicability in several electrochemical energy storage systems, such as fuel cells, batteries, and supercapacitors. This review provides a comprehensive comparison of different synthesis approaches of MO nanosheets, as well their suitability in several energy storage applications. Among recent improvements in energy storage systems, micro-supercapacitors, and several hybrid storage systems are rapidly emerging. MO nanosheets can be employed as electrode and catalyst material to improve the performance parameters of energy storage devices. Finally, this review outlines and discusses the prospects, future challenges, and further direction for research and applications of metal oxide nanosheets.

Novel Preoxidation-Assisted Mechanism to Preciously Form and Disperse Bi2O3 Nanodots in Carbon Nanofibers for Ultralong-Life and High-Rate Sodium Storage

Metal oxides, as promising electrode materials for sodium-ion batteries, usually need to be formed by exposure to oxygen, which usually thermally corrodes the carbon material with which they are compounded, reducing their flexibility and electrical conductivity. Herein, we present for the first time a preoxidation-assisted mechanism to prepare bismuth oxide and carbon nanofibers (Bi₂O₃@C-NFs) by electrospinning, using Bi₂S₃ nanorods as multifunctional templates. The bismuth could be oxidized by C═O bonds formed through the cyclization reaction in the high-temperature calcination process, effectively avoiding thermal corrosion of carbon in oxygen atmosphere at high temperature. More importantly, the uniformly distributed Bi₂O₃ nanodots and longitudinal tunnels are formed inside the S- and N-doped carbon nanofibers with the continuous diffusion of Bi generated from the decomposition of Bi₂S₃ nanorods and the conversion to Bi─O bonds with C═O bonds being broken. Benefiting from the structural and composition merits arising from preoxidation, Bi₂O₃@C-NFs self-supporting anodes show high specific capacity (439 mAh g^-1 at 0.05 A g^-1), superior rate performance (243 mAh g^-1 at a current density of 20 A g^-1), and outstanding cycling stability (211 mAh g^-1 after 2000 cycles at 5 A g^-1). The effective combination of the well-established electrospinning technology and the preoxidation assisted mechanism provides a new way for the preparation of metal oxide and carbon composites.

Heterostructure Engineering of 2D Superlattice Materials for Electrocatalysis

Exploring low-cost and high-efficient electrocatalyst is an exigent task in developing novel sustainable energy conversion systems, such as fuel cells and electrocatalytic fuel generations. 2D materials, specifically 2D superlattice materials focused here, featured highly accessible active areas, high density of active sites, and high compatibility with property-complementary materials to form heterostructures with desired synergetic effects, have demonstrated to be promising electrocatalysts for boosting the performance of sustainable energy conversion and storage devices. Nevertheless, the reaction kinetics, and in particular, the functional mechanisms of the 2D superlattice-based catalysts yet remain ambiguous. In this review, based on the recent progress of 2D superlattice materials in electrocatalysis applications, the rational design and fabrication of 2D superlattices are first summarized and the application of 2D superlattices in electrocatalysis is then specifically discussed. Finally, perspectives on the current challenges and the strategies for the future design of 2D superlattice materials are outlined. This review attempts to establish an intrinsic correlation between the 2D superlattice heterostructures and the catalytic properties, so as to provide some insights into developing high-performance electrocatalysts for next-generation sustainable energy conversion and storage.

Bridging 1D Inorganic and Organic Synthesis to Fabricate Ultrathin Bismuth-Based Nanotubes with Controllable Size as Anode Materials for Secondary Li Batteries

The growth of ultrathin 1D inorganic nanomaterials with controlled diameters remains challenging by current synthetic approaches. A polymer chain templated method is developed to synthesize ultrathin Bi₂ O₂ CO₃ nanotubes. This formation of nanotubes is a consequence of registry between the electrostatic absorption of functional groups on polymer template and the growth habit of Bi₂ O₂ CO₃ . The bulk bismuth precursor is broken into nanoparticles and anchored onto the polymer chain periodically. These nanoparticles react with the functional groups and gradually evolve into Bi₂ O₂ CO₃ nanotubes along the chain. 5.0 and 3.0 nm tubes with narrow diameter deviation are synthesized by using branched polyethyleneimine and polyvinylpyrrolidone as the templates, respectively. Such Bi₂ O₂ CO₃ nanotubes show a decent lithium-ion storage capacity of around 600 mA h g^-1 at 0.1 A g^-1 after 500 cycles, higher than other reported bismuth oxide anode materials. More interestingly, the Bi materials developed herein still show decent capacity at very low temperatures, that is, around 330 mA h g^-1 (-22 °C) and 170 mA h g^-1 (-35 °C) after 75 cycles at 0.1 A g^-1 , demonstrating their promising potential for practical application in extreme conditions.

Facile synthesis of electrocatalytically active bismuth oxide nanosheets for detection of palladium traces in pharmaceutical wastewater

Current synthesis routes of bismuth oxide nanosheets (BiONS) are relatively complicated, requiring the use of halogens or metalloids. Herein, a facile method to synthesize BiONS without the addition of halogens or other metalloids was developed. The synthesized BiONS were identified to have flake-shaped structures (300-1000 nm in width) with the thickness of 6-10 nm, which were predominantly made of β-Bi₂O₃. Such BiONS were applied to modify the surface of screen-printed carbon electrodes (BiONS-SPCEs) for the development of a robust palladium (Pd²⁺) sensor. After optimizing the electrochemical parameters of the sensor, it was found that the linear sensor response range and limit of detection for Pd²⁺ were 40-400 and 1.4 ppb, respectively. The electrocatalytic activity of the Pd²⁺-sensor was validated in the competing environment of other metal and metalloid ions. Real samples collected during a Pd recovery process from pharmaceutical wastewater were used to verify the application of BiONS-SPCEs in control of palladium recovery process. The quantitative results of post recovery palladium concentrations obtained using BiONS-SPCEs in treated pharmaceutical wastewater samples were in good agreement with those obtained by inductively coupled plasma-optical emission spectrometry (ICP-OES). Thus, such Pd²⁺-sensor provided the possibility of on-site process control of complex industrial samples for obtaining near-instant information that would lead to better management of resources used in the process, and same time assure environmental standards for both recovered products and processed discharge.

A nanocubicle-like 3D adsorbent fabricated by in situ growth of 2D heterostructures for removal of aromatic contaminants in water

Focusing on the emergence of organic pollutants in aqueous environments, attempts to assemble two-dimensional (2D) materials into three-dimensional (3D) structures are expected to improve their pollution control performance. However, most 3D heterostructural nanomaterials are constructed by mechanical mixing methods, which result in structures that are randomly arranged and prone to collapse. Two typical 2D carbon materials, reduced graphene oxide (rGO) and covalent triazine frameworks (CTFs), have exhibited excellent effects in the fields of contaminant adsorption and photocatalysis, respectively. However, their regular packing structure could not provide an interconnected pore network suitable for the diffusion or adsorption of pollutants. In this study, a series of heterostructures named rGCs were fabricated by direct growth of 2D CTFs with different ratios on the surface of rGO layers. The rGCs were designed to remove trace concentrations of naphthalene (NAP) and benzophenone (BP) from water, which can be regenerated under sunlight. rGC-20, in which nanocubicle-like 3D heterostructures were successfully constructed, not only adsorbed NAP and BP with superb normalized adsorption capacities (5000-5300 μmol/g) but also could be regenerated with an exceptional percentage recovery of 90-95% in the 4th cycle. The microenvironment created in nanocubicle-like 3D heterostructures enhances the adsorption of pollutants, the excitation of electrons and utilization of radicals, which further promotes the adsorption and photocatalysis of rGCs. This work provides a promising adsorbent with outstanding adsorption-regeneration ability for aromatic contaminant removal from water. DATA AVAILABILITY: The main data that support the findings of this study are available from the article and its Supplementary Information. Extra data are available from the corresponding author on request.

Pseudocapacitance-boosted ultrafast and stable Na-storage in NiTe2 coupled with N-doped carbon nanosheets for advanced sodium-ion half/full batteries

Developing high-rate and durable anode materials for sodium-ion batteries (SIBs) is still a challenge because of the larger ion radius of sodium compared with the lithium ion during charge-discharge processes. Herein, NiTe₂ coupled with N-doped carbon (NiTe₂/NC) hexagonal nanosheets has been fabricated through a solvothermal and subsequent carbonisation strategy. This unique hexagonal nanosheet structure offers abundant active sites and contact area to the electrolyte, which could shorten the Na⁺ diffusion path. The heterostructured N-doping carbon improves the electrochemical conductivity and accelerates the kinetics of Na⁺ transportation. Electrochemical analysis shows that the charge-discharge process is controlled by the pseudocapacitive behavior thus leading to high-rate capability and long lifespan in half batteries. As expected, high capacities of 311 mA h g^-1 to 217 mA h g^-1 at 5 A g^-1 to 10 A g^-1 are maintained after 800 and 1200 cycles, respectively. Furthermore, a full battery equipped with a Na₃V₂(PO₄)₂O₂F cathode and a NiTe₂/NC anode offers a maximum energy density of 104 W h kg^-1 and a maximum power density of 9116 W kg^-1. The results clearly show that the NiTe₂/NC hexagonal nanosheet with superior Na storage properties is an advanced new material for energy storage systems.

Conversion-Alloying Anode Materials for Sodium Ion Batteries

The past decade has witnessed a rapidly growing interest toward sodium ion battery (SIB) for large-scale energy storage in view of the abundance and easy accessibility of sodium resources. Key to addressing the remaining challenges and setbacks and to translate lab science into commercializable products is the development of high-performance anode materials. Anode materials featuring combined conversion and alloying mechanisms are one of the most attractive candidates, due to their high theoretical capacities and relatively low working voltages. The current understanding of sodium-storage mechanisms in conversion-alloying anode materials is presented here. The challenges faced by these materials in SIBs, and the corresponding improvement strategies, are comprehensively discussed in correlation with the resulting electrochemical behavior. Finally, with the guidance and perspectives, a roadmap toward the development of advanced conversion-alloying materials for commercializable SIBs is created.

Nano Polymorphism-Enabled Redox Electrodes for Rechargeable Batteries

Nano polymorphism (NPM), as an emerging research area in the field of energy storage, and rechargeable batteries, have attracted much attention recently. In this review, the recent progress on the composition and formation of polymorphs, and the evolution processes of different redox electrodes in rechargeable metal-ion, metal-air, and metal-sulfur batteries are highlighted. First, NPM and its significance for rechargeable batteries are discussed. Subsequently, the current NPM modulation strategies of different types of representative electrodes for their corresponding rechargeable battery applications are summarized. The goal is to demonstrate how NPM could tune the intrinsic material properties, and hence, improve their electrochemical activities for each battery type. It is expected that the analysis of polymorphism and electrochemical properties of materials could help identify some "processing-structure-properties" relationships for material design and performance enhancement. Lastly, the current research challenges and potential research directions are discussed to offer guidance and perspectives for future research on NPM engineering.

Heterostructured bismuth oxide/hexagonal-boron nitride nanocomposite: A disposable electrochemical sensor for detection of flutamide

Aquatic contamination from the accumulation of pharmaceuticals has induced severe toxicological impact to the ecological environment, especially from non-steroidal anti-inflammatory drugs (NSAIDs). Real-time monitoring of flutamide, which is a class of NSAIDs, is very significant in environmental protection. In this work, we have synthesized the hexagonal-h boron nitride decorated on bismuth oxide (Bi₂O₃/h-BN) based nanocomposite for the effective electrochemical detection of flutamide (FTM). The structural and morphological information of the heterostructured Bi₂O₃/h-BN nanocomposite was analyzed by using a sequence of characterization methods. Voltammetric techniques were used to evaluate the analytical performance of the Bi₂O₃/h-BN modified screen-printed carbon electrode (SPCE) for the FTM detection. The Bi₂O₃/h-BN modified SPCE displays a synergetic catalytic effect for the reduction of FTM due to large surface area, numerous active sites, fast charge transfer and abundant defects. The proposed electrochemical sensing platform demonstrates high selectivity, low detection limit (9.0 nM), good linear ranges (0.04-87 μM) and short response time for the detection of FTM. The feasibility of the electrochemical sensor has been proved by the successful application to determine FTM in environmental samples.

Bi-Based Electrode Materials for Alkali Metal-Ion Batteries

Alkali metal (Li, Na, K) ion batteries with high energy density are urgently required for large-scale energy storage applications while the lack of advanced anode materials restricts their development. Recently, Bi-based materials have been recognized as promising electrode candidates for alkali metal-ion batteries due to their high volumetric capacity and suitable operating potential. Herein, the latest progress of Bi-based electrode materials for alkali metal-ion batteries is summarized, mainly focusing on synthesis strategies, structural features, storage mechanisms, and the corresponding electrochemical performance. Particularly, the optimization of electrode-electrolyte interphase is also discussed. In addition, the remaining challenges and further perspectives of Bi-based electrode materials are outlined. This review aims to provide comprehensive knowledge of Bi-based materials and offer a guideline toward more applications in high-performance batteries.

Strongly interfacial-coupled 2D-2D TiO2/g-C3N4 heterostructure for enhanced visible-light induced synthesis and conversion

Two-dimensional (2D) nanosheet-based nanocomposites have attracted intensive interest owing to the unique electronic and optical properties from their constituent phases and the synergistic effect from the heterojunctions. In this study, an interfacial coupled TiO₂/g-C₃N₄ 2D-2D heterostructure has been prepared via in situ growth of ultrathin 2D-TiO₂ on dispersed g-C₃N₄ nanosheets. This strongly coupled 2D-2D TiO₂/g-C₃N₄, different from the weakly bonded 2D-TiO₂/g-C₃N₄ heterostructures produced by mechanical mixing, has unique electronic structures and chemical states due to strong interlayer charge transfer, confirmed by both experimental and theoretical analyses. Significantly enhanced visible-light responses have been observed, indicating a great potential for visible-light induced photosynthesis and photocatalysis. For benzylamine coupling reactions under visible-light irradiation, 80 % yield rate has been achieved, superior to ∼30 % yield rate when adopting either 2D-TiO₂ or g-C₃N₄ structure. The enhanced photocatalytic activity can be attributed to the adequate separation of photo-generated electrons at the strongly coupled 2D-2D heterojunction interfaces.

Flexible Carbon-Fiber/Semimetal Bi Nanosheet Arrays as Separable and Recyclable Plasmonic Photocatalysts and Photoelectrocatalysts

In this work, we prepared flexible carbon-fiber/semimetal Bi nanosheet arrays from solvothermal-synthesized carbon-fiber/Bi₂O₂CO₃ nanosheet arrays via a reductive calcination process. The flexible carbon-fiber/semimetal Bi nanosheet arrays can function as photocatalysts and photoelectrocatalysts for 2,4-dinitorphenol oxidation. Compared with carbon-fiber/Bi₂O₂CO₃ nanosheet arrays, the newly designed flexible carbon-fiber/semimetal Bi nanosheet arrays show enhanced ultraviolet-visible (UV-vis) light absorption efficiency and photocurrent, photocatalytic, and photoelectrocatalytic activities. Photocatalytic analyses indicate that the surface plasmon resonance (SPR) of semimetal Bi occurs under solar-simulated light irradiation during the photocatalytic process. The carbon-fiber traps the hot electrons exerted from the SPR of semimetal Bi and creates holes in the semimetal Bi nanosheets, which boosts the photocatalytic activity of the carbon fiber through plasmonic sensitization. Both photocatalytic experiments and density functional theory (DFT) calculations indicate that the electrons transferred to the carbon fiber and the holes created in semimetal Bi contribute to the formation of •O₂^- and •OH, respectively. The synergistic effect between electrocatalysis and photocatalysis under the solar-simulated light results in almost complete degradation of 2,4-dinitorphenol during the photoelectrocatalytic process. This work realizes a non-noble-metal plasmonic catalyst and provides a new avenue for the commercialization of photocatalysis and photoelectrocatalysis using the separable and recyclable carbon-fiber/semimetal Bi nanosheet arrays in the environment-related field.

Zero-Dimensional Ordered Sr2CoMoO6-δ Double Perovskite as High-Rate Anion Intercalation Pseudocapacitance

In quest of a stable structure throughout redox reactions, an approach of B-site ordering (0D arrangement) of cations in double perovskites is adopted. Here, we report B-site cation ordering in double perovskite Sr₂CoMoO_6-δ (DP-SCM) that tends to a favorable rock salt structure (0D arrangement). The synergy of Co/Mo having good redox ability further facilitates high oxygen mobility. A high content of oxygen vacancy examined using XPS and EPR facilitates a high oxygen anion diffusion rate (2.03 × 10^-11 cm² s^-1). Moreover, fast kinetics (ΔE_P ≈ 0.013 V@ 1 mV s^-1) of charge storage prohibits any phase transformation reflecting the excellent cycle life (125% retention up to 5000 cycles). Such fast kinetics is majorly furnished from anion intercalation with little involvement from double layer mechanism (C_dl ≈ 42.1 F g^-1). DP-SCM achieves a resultant capacitance of 747 F g^-1@ 1 A g^-1 with a rate capability of 56% up to 10 A g^-1. Motivated by outstanding performance of DP-SCM electrodes, a symmetric cell is assembled with a 1.4 V operating potential that delivers a high energy density of 64 Wh kg^-1@855 W kg^-1. This work on double perovskites suggests that the advance understanding of cation ordering and charge storage mechanism can provide a new direction to fabricate highly capacitive electrode materials.

Two-Dimensional Materials to Address the Lithium Battery Challenges

Despite the ever-growing demand in safe and high power/energy density of Li⁺ ion and Li metal rechargeable batteries (LIBs), materials-related challenges are responsible for the majority of performance degradation in such batteries. These challenges include electrochemically induced phase transformations, repeated volume expansion and stress concentrations at interfaces, poor electrical and mechanical properties, low ionic conductivity, dendritic growth of Li, oxygen release and transition metal dissolution of cathodes, polysulfide shuttling in Li-sulfur batteries, and poor reversibility of lithium peroxide/superoxide products in Li-O₂ batteries. Owing to compelling physicochemical and structural properties, in recent years two-dimensional (2D) materials have emerged as promising candidates to address the challenges in LIBs. This Review highlights the cutting-edge advances of LIBs by using 2D materials as cathodes, anodes, separators, catalysts, current collectors, and electrolytes. It is shown that 2D materials can protect the electrode materials from pulverization, improve the synergy of Li⁺ ion deposition, facilitate Li⁺ ion flux through electrolyte and electrode/electrolyte interfaces, enhance thermal stability, block the lithium polysulfide species, and facilitate the formation/decomposition of Li-O₂ discharge products. This work facilitates the design of safe Li batteries with high energy and power density by using 2D materials.