Layer-Tunable Phosphorene Modulated by the Cation Insertion Rate as a Sodium-Storage Anode

An updated review of few-layer black phosphorus serving as a promising photocatalyst: synthesis, modification and applications

Semiconductor photocatalysts represent a potential strategy to simultaneously solve the global energy shortage and environmental pollution, and black phosphorus (BP) has gained widespread applications in photocatalysis due to its high hole mobility, strong light trapping capabilities, and adjustable band gap. Nevertheless, the original material exhibits unsatisfactory photocatalytic activity in terms of low carrier separation efficiency, weak environmental stability, and difficult to control layer thickness. The following review briefly presents the fundamental characteristics and extensively discusses the synthesis methods and modification strategies for few-layer black phosphorus (FL-BP). Furthermore, various applications of composite photocatalysts derived from FL-BP such as water splitting, pollutant degradation, the carbon dioxide reduction reaction (CO2RR), phototherapy, bacterial disinfection, N2 fixation, and hydrogenation reactions are reviewed. Finally, the opportunities and challenges for the development and further investigation of advanced FL-BP-based photocatalysts are also presented.

High-Yield Exfoliation of Stanene Nanodots for High-Performance Organic Light-Emitting Diodes

Stanene nanodots (SnNDs) derived from layered tin have attracted considerable interest due to their conveniently tunable bandgap and topological superconductivity. However, high-yield exfoliation of ultrathin SnNDs is still a challenge due to the short layer spacing and strong binding energy. In this work, atomically thin SnNDs with a uniform size of 2.3 nm are successfully prepared by utilizing imidazolium ionic liquid-assisted exfoliation. The obtained SnNDs possess a wide bandgap of 2.69 eV, along with notable solvent compatibility (well dispersed in both polar and nonpolar solvents) and excellent stability. Furthermore, we construct Ir(ppy)3-based green OLED with hybridizing SnNDs and graphene oxide (GO) as the hole injection layer (HIL). It proves that the application of SnNDs helps to modulate the work function and passivate surface defects of GO, increasing hole mobility and thereby improving the device performance. Compared to the PEDOT:PSS-based control device, the optimized SnNDs-GO-based OLED demonstrates an improvement of 6.56, 41.06, and 8.16% in current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE), respectively. This work not only introduces a new approach to preparing 2D SnNDs but also creates a novel HIL material for OLED devices.

Pd-intercalated black phosphorus: An efficient electrocatalyst for CO2 reduction

Nanoconfined catalysts enhance stabilization of reaction intermediates, facilitate electron transfer, and safeguard active centers, leading to superior electrocatalytic activity, particularly in CO2 reduction reactions (CO2RR). Despite their effectiveness, crafting nanoconfined catalysts is challenging due to unclear formation mechanisms. In this study, we introduce an electrochemical method to grow Pd clusters within the interlayers of two-dimensional black phosphorus, creating Pd cluster-intercalated black phosphorus (Pd-i-BP) as an electrocatalyst. Using in situ electrochemical liquid phase transmission electron microscopy (EC-TEM), we revealed the synthesis mechanism of Pd-i-BP, involving electrochemically driven Pd ion intercalation followed by reduction within the BP layers. The Pd-i-BP electrocatalyst exhibits exemplary CO2-to-formate conversion, achieving 90% Faradaic efficiency for formate production, owing to its distinct nanoconfined structure that stabilizes intermediates and enhances electron transfer. Density functional theory (DFT) calculations underscore the structural benefits for enhancing intermediate adsorption and catalyzing the reaction. Our insights deepen understanding of nanoconfined material synthesis, promising advanced, high-efficiency catalysts.

Intercalation in 2D materials and in situ studies

Intercalation of atoms, ions and molecules is a powerful tool for altering or tuning the properties - interlayer interactions, in-plane bonding configurations, Fermi-level energies, electronic band structures and spin-orbit coupling - of 2D materials. Intercalation can induce property changes in materials related to photonics, electronics, optoelectronics, thermoelectricity, magnetism, catalysis and energy storage, unlocking or improving the potential of 2D materials in present and future applications. In situ imaging and spectroscopy technologies are used to visualize and trace intercalation processes. These techniques provide the opportunity for deciphering important and often elusive intercalation dynamics, chemomechanics and mechanisms, such as the intercalation pathways, reversibility, uniformity and speed. In this Review, we discuss intercalation in 2D materials, beginning with a brief introduction of the intercalation strategies, then we look into the atomic and intrinsic effects of intercalation, followed by an overview of their in situ studies, and finally provide our outlook.

Recent Progress on Synthesis and Properties of Black Phosphorus and Phosphorene As New-Age Nanomaterials for Water Decontamination

Concerted efforts have been made in recent years to find solutions to water and wastewater treatment challenges and eliminate the difficulties associated with treatment methods. Various techniques are used to ensure the recycling and reuse of water resources. Owing to their excellent chemical, physical, and biological properties, nanomaterials play an important role when integrated into water/wastewater treatment technologies. Black phosphorus (BP) is a potential nanomaterial candidate for water and wastewater treatment, especially its monolayer 2D derivative called phosphorene. Phosphorene offers relative adjustability in its direct bandgap, high charge carrier mobility, and improved in-plane anisotropy compared to the most extensively studied 2D nanomaterials. In this study, we examined the physical and chemical characteristics and synthetic processes of BP and phosphorene. We provide an overview of the latest advancements in the main applications of BP and phosphorene in water/wastewater treatment, which are categorized as photocatalytic, adsorption, and membrane filtration processes. Additionally, we explore the existing difficulties in the integration of BP and phosphorene into water/wastewater treatment technologies and prospects for future research in this field. In summary, this review highlights the ongoing necessity for significant research efforts on the integration of BP and phosphorene in water and wastewater applications.

Electrochemical exfoliation of 2D materials beyond graphene

After the discovery of graphene in 2004, the field of atomically thin crystals has exploded with the discovery of thousands of 2-dimensional materials (2DMs) with unique electronic and optical properties, by making them very attractive for a broad range of applications, from electronics to energy storage and harvesting, and from sensing to biomedical applications. In order to integrate 2DMs into practical applications, it is crucial to develop mass scalable techniques providing crystals of high quality and in large yield. Electrochemical exfoliation is one of the most promising methods for producing 2DMs, as it enables quick and large-scale production of solution processable nanosheets with a thickness well below 10 layers and lateral size above 1 μm. Originally, this technique was developed for the production of graphene; however, in the last few years, this approach has been successfully extended to other 2DMs, such as transition metal dichalcogenides, black phosphorous, hexagonal boron nitride, MXenes and many other emerging 2D materials. This review first provides an introduction to the fundamentals of electrochemical exfoliation and then it discusses the production of each class of 2DMs, by introducing their properties and giving examples of applications. Finally, a summary and perspective are given to address some of the challenges in this research area.

Recent Advances in Black Phosphorous-Based Photocatalysts for Degradation of Emerging Contaminants

The recalcitrant nature of emerging contaminants (ECs) in aquatic environments necessitates the development of effective strategies for their remediation, given the considerable impacts they pose on both human health and the delicate balance of the ecosystem. Semiconductor-based photocatalytic technology is recognized for its dual benefits in effectively addressing both ECs and energy-related challenges simultaneously. Among the plethora of photocatalysts, black phosphorus (BP) stands as a promising nonmetallic candidate, offering a host of advantages including its tunable direct band gap, broad-spectrum light absorption capabilities, and exceptional charge mobility. Nevertheless, pristine BP frequently underperforms, primarily due to issues related to its limited ambient stability and the rapid recombination of photogenerated electron-hole pairs. To overcome these challenges, substantial research efforts have been devoted to the creation of BP-based photocatalysts in recent years. However, there is a noticeable absence of reviews regarding the advancement of BP-based materials for the degradation of ECs in aqueous solutions. Therefore, to fill this gap, a comprehensive review is undertaken. In this review, we first present an in-depth examination of the fabrication processes for bulk BP and BP nanosheets (BPNS). The review conducts a thorough analysis and comparison of the merits and limitations inherent in each method, thereby delineating the most auspicious avenues for future research. Then, in line with the pathways followed by photogenerated electron-hole pairs at the interface, BP-based photocatalysts are systematically categorized into heterojunctions (Type I, Type II, Z-scheme, and S-scheme) and hybrids, and their photocatalytic performances against various ECs and the corresponding degradation mechanisms are comprehensively summarized. Finally, this review presents personal insights into the prospective avenues for advancing the field of BP-based photocatalysts for ECs remediation.

Advanced Multilayered Electrode with Planar Building Blocks Structure for High-Performance Lithium-Ion Storage

To achieve the high-performance of lithium-ion battery, the optimization of electrode materials has generally been considered as the one of the important methods. But most of those works pay attention to the new materials preparation or interface modification rather than the structural innovation. Here, an advanced electrode (GDY/BP/GDY-E) with multilevel layered architecture constructed by planar building blocks stacking structure has been designed and fabricated to explore the structure design of the electrode. This new structure is assembled by graphdiyne (GDY) and black phosphorus (BP) in parallel to form a building block (GDY/BP/GDY). The electric fields between the two GDY sides of the planar building block structure contribute to the superior migration dynamics of lithium ions and desirable pseudocapacitance behavior. Meanwhile, the planar stacking structure of GDY/BP/GDY can efficiently inhibit volume expansion of BP and a series of parasitic reactions of electrolytes during the long-term cycling. The advanced GDY/BP/GDY-E exhibits excellent high-rate performance (1418.8 mAh g-1 at 0.1 A g-1 ) and cycling stability (391.7 mAh g-1 after 5000 cycles at 10 A g-1 ). Such structural design of electrode materials shows a new way to develop high-performance electrodes.

Renaissance of elemental phosphorus materials: properties, synthesis, and applications in sustainable energy and environment

The polymorphism of phosphorus-based materials has garnered much research interest, and the variable chemical bonding structures give rise to a variety of micro and nanostructures. Among the different types of materials containing phosphorus, elemental phosphorus materials (EPMs) constitute the foundation for the synthesis of related compounds. EPMs are experiencing a renaissance in the post-graphene era, thanks to recent advancements in the scaling-down of black phosphorus, amorphous red phosphorus, violet phosphorus, and fibrous phosphorus and consequently, diverse classes of low-dimensional sheets, ribbons, and dots of EPMs with intriguing properties have been produced. The nanostructured EPMs featuring tunable bandgaps, moderate carrier mobility, and excellent optical absorption have shown great potential in energy conversion, energy storage, and environmental remediation. It is thus important to have a good understanding of the differences and interrelationships among diverse EPMs, their intrinsic physical and chemical properties, the synthesis of specific structures, and the selection of suitable nanostructures of EPMs for particular applications. In this comprehensive review, we aim to provide an in-depth analysis and discussion of the fundamental physicochemical properties, synthesis, and applications of EPMs in the areas of energy conversion, energy storage, and environmental remediation. Our evaluations are based on recent literature on well-established phosphorus allotropes and theoretical predictions of new EPMs. The objective of this review is to enhance our comprehension of the characteristics of EPMs, keep abreast of recent advances, and provide guidance for future research of EPMs in the fields of chemistry and materials science.

Electrochemically Engineering a Single-Crystal Nickel-Rich Layered Cathode

Nickel-rich layered electrode material has been attracting significant attention owing to its high specific capacity as a cathode for lithium-ion batteries. Generally, the high-nickel ternary precursors obtained by traditional coprecipitation methods are micron-scale. In this work, the submicrometer single-crystal LiNi_0.8Co_0.1Mn_0.1O₂ (NCM) cathode is efficiently prepared by electrochemically anodic oxidation followed by a molten-salt-assisted reaction without the need of extreme alkaline environments and complex processes. More importantly, when prepared under optimal voltage (10 V), single-crystal NCM exhibits a moderate particle size (∼250 nm) and strong metal-oxygen bonds due to reasonable and balanced crystal nucleation/growth rate, which are conducive to greatly enhancing the Li⁺ diffusion kinetics and structure stability. Given that a good discharge capacity of 205.7 mAh g^-1 at 0.1 C (1 C = 200 mAh g^-1) and a superior capacity retention of 87.7% after 180 cycles at 1 C are obtained based on the NCM electrode, this strategy is effective and flexible for developing a submicrometer single-crystal nickel-rich layered cathode. Besides, it can be adopted to elevate the performance and utilization of nickel-rich cathode materials.

Controllable Synthesis of 2D Materials by Electrochemical Exfoliation for Energy Storage and Conversion Application

2D materials have captured much recent research interest in a broad range of areas, including electronics, biology, sensors, energy storage, and others. In particular, preparing 2D nanosheets with high quality and high yield is crucial for the important applications in energy storage and conversion. Compared with other prevailing synthetic strategies, the electrochemical exfoliation of layered starting materials is regarded as one of the most promising and convenient methods for the large-scale production of uniform 2D nanosheets. Here, recent developments in electrochemical delamination are reviewed, including protocols, categories, principles, and operating conditions. State-of-the-art methods for obtaining 2D materials with small numbers of layers-including graphene, black phosphorene, transition metal dichalcogenides and MXene-are also summarized and discussed in detail. The applications of electrochemically exfoliated 2D materials in energy storage and conversion are systematically reviewed. Drawing upon current progress, perspectives on emerging trends, existing challenges, and future research directions of electrochemical delamination are also offered.

MXene: fundamentals to applications in electrochemical energy storage

A new, sizable family of 2D transition metal carbonitrides, carbides, and nitrides known as MXenes has attracted a lot of attention in recent years. This is because MXenes exhibit a variety of intriguing physical, chemical, mechanical, and electrochemical characteristics that are closely linked to the wide variety of their surface terminations and elemental compositions. Particularly, MXenes are readily converted into composites with materials including oxides, polymers, and CNTs, which makes it possible to modify their characteristics for a variety of uses. MXenes and MXene-based composites have demonstrated tremendous promise in environmental applications due to their excellent reducibility, conductivity, and biocompatibility, in addition to their well-known rise to prominence as electrode materials in the energy storage sector. The remarkable characteristics of 2D MXene, including high conductivity, high specific surface area, and enhanced hydrophilicity, account for the increasing prominence of its use in storage devices. In this review, we highlight the most recent developments in the use of MXenes and MXene-based composites for electrochemical energy storage while summarizing their synthesis and characteristics. Key attention is paid to applications in supercapacitors, batteries, and their flexible components. Future research challenges and perspectives are also described.

Progress in the preparation, application, and recycling of black phosphorus

Black phosphorus nanosheets (BPNSs) are a new member of the nanomaterial family, and they have good development potential in electrochemistry, electronics, optoelectronics, environmental protection, biomedical, and other fields because of their bandgap width, high anisotropy, broad optical absorption, high carrier mobility and many other features. Although many articles have been published about the preparation and application of BPNSs, these aspects have not been elucidated, and we aimed to fill this knowledge gap in this review. First, we used VOSviewer software to sort out articles published in the past 5 years and drew a literature map, which allowed us to sort out the relationship between various studies related to BPNSs, and reflect on the research focus in recent years. Because BPNSs must be made from black phosphorus (BP), and BPNSs are a nano form of BP, the collation of the BP preparation scheme was also helpful for the related research on BPNSs. This paper introduces the preparation of bulk BP and BPNSs, analyzes and compares the advantages and disadvantages of each method, and points out the most promising methods in the future. Then, we propose improvement directions for this method. We also introduce the characterization of BPNSs and combine it with the subsequent photocatalytic application of BPNSs. As a new material, the effect of BPNSs on the environment is still unknown; thus, an end treatment scheme for BPNSs is summarized according to existing methods. Based on the experience of nanomaterial treatment, this paper proposes a research focus for the end treatment of BPNSs in the future, providing a reference scheme for the end treatment of other nanomaterials. Finally, we summarize the full text and propose recommended methods and improvement plans.

Recent Progress in Aqueous Ammonium-Ion Batteries

Batteries using a water-based electrolyte have the potential to be safer, more durable, less prone to thermal runaways, and less costly than current lithium batteries using an organic solvent. Among the possible aqueous battery options, ammonium-ion batteries (AIBs) are very appealing because the base materials are light, safe, inexpensive, and widely available. This review gives a concise and useful survey of recent progress on emerging AIBs, starting with a brief overview of AIBs, followed by cathode materials, anode materials, electrolytes, and various devices based on ammonium-ion storage. Aside from summarizing the most updated electrodes/electrolytes in AIBs, this review highlights fundamental mechanistic studies in AIBs and state-of-the art applications of ammonium-ion storage. The present work reviews various theoretical efforts and the spectrum studies that have been used to explore ionic transport kinetics, electrolyte structure, solvation behavior of ammonium ions, and the intercalation mechanism in the host structure. Furthermore, diverse applications of ammonium-ion storage apart from aqueous AIBs are discussed, including flexible AIBs, AIBs that can operate across a wide temperature range, ammonium-ion supercapacitors, and battery-supercapacitor hybrid devices. Finally, the review is concluded with perspectives of AIBs, challenges remaining in the field, and possible research directions to address these challenges to boost the performance of AIBs for real-world practical applications.

Sodium-Ion Battery with a Wide Operation-Temperature Range from -70 to 100 °C

Sodium-ion batteries (SIBs), as one of the potential candidates for grid-scale energy storage systems, are required to tackle extreme weather conditions. However, the all-weather SIBs with a wide operation-temperature range are rarely reported. Herein, we propose a wide-temperature range SIB, which involves a carbon-coated Na₄ Fe₃ (PO₄ )₂ P₂ O₇ (NFPP@C) cathode, a bismuth (Bi) anode, and a diglyme-based electrolyte. We demonstrate that solvated Na⁺ can be directly stored by the Bi anode via an alloying reaction without the de-solvent process. Furthermore, the NFPP@C cathode exhibits a high Na⁺ diffusion coefficient at low temperature. As a result, the Bi//NFPP@C battery exhibits perfect low-temperature behavior. Even at -70 °C, this battery still delivers 70.19 % of the room-temperature capacity. Furthermore, benefitting from the high boiling point of the electrolyte, this battery also works well at a high temperature of up to 100 °C. These results are encouraging for the further exploration of wide-temperature range SIBs.

Lattice Matching and Halogen Regulation for Synergistically Induced Uniform Zinc Electrodeposition by Halogenated Ti3C2 MXenes

Dendrite growth and low Coulombic efficiency caused by uneven diffusion and electrodeposition of Zn²⁺ ions have emerged as a barrier to exploit the Zn metal anode. In this work, we demonstrate the stoichiometric halogenated MXenes (Ti₃C₂Cl₂, Ti₃C₂Br₂, and Ti₃C₂I₂) as an artificial layer that can induce the uniform Zn deposition. The efficient redistribution effect results from the coherent heterogeneous interface reconstruction and regulated ion tiling by halogen surficial termination. The synergetic effects of high lattice matching (90%) between the adopted MXenes and Zn, as well as the positive halogen regulation, Zn²⁺ ions are guided to nucleate uniformly on the most extensive (000l) crystal plane of the MXene matrix and grow in a planar manner. In terms of Zn ion regulation, Cl termination is found to be more effective than O/F, Br, and I due to its moderate adsorption and diffusion coefficiency for Zn²⁺ ions. The Ti₃C₂Cl₂-Zn anode achieves a life extension of over 12 times (840 h at 2 mA cm^-2//1 mAh cm^-2) over that of the bare Zn anode and serves more than 9000 cycles in a battery with a Ti₃C₂I₂ cathode at a high rate of 3 A g^-1. Given the abundance of lattice parameters and terminations of MXene materials, the developed strategy is expected to be extended to other metal anode systems.

Synthesis and stabilization of black phosphorus and phosphorene: recent progress and perspectives

Two-dimensional black phosphorus (BP) has triggered tremendous research interest owing to its unique crystal structure, high carrier mobility, and tunable direct bandgap. Preparation of few-layer BP with high quality and stability is very important for its related research and applications in biomedicine, electronics, and optoelectronics. In this review, the synthesis methods of BP, including the preparation of bulk BP crystal which is an important raw material for preparing few-layer BP, the popular top-down methods, and some direct growth strategies of few-layer BP are comprehensively overviewed. Then chemical ways to enhance the stability of few-layer BP are concretely introduced. Finally, we propose a selection rule of preparation methods of few-layer BP according to the requirement of specific BP properties for different applications. We hope this review would bring some insight for future researches on BP and contributes to the acceleration of BP's commercial progress.

Toward a Practical Zn Powder Anode: Ti3C2Tx MXene as a Lattice-Match Electrons/Ions Redistributor

The renaissance of aqueous Zn ion batteries has drawn intense attention to Zn metal anode issues, including dendrites growth, dead Zn, low efficiency, and other parasitic reactions. However, against the widely used 2D Zn foil, in fact, the Zn powder anode is a more practical choice for Zn-based batteries in industrial applications, but the related solutions are rarely investigated. Herein, we focus on the Zn powder anode and disclose its unknown failure mechanism different from Zn foils. By utilization of 2D flexible conductive Ti₃C₂Tx MXene flakes with hexagonal close-packed lattice as electrons and ions redistributor, a stable and highly reversible Zn powder anode without dendrite growth and low polarization is constructed. Low lattice mismatch (∼10%) enables a coherent heterogeneous interface between the (0002) plane of deposited Zn and (0002) plane of the Ti₃C₂Tx MXene. Thus, the Zn²⁺ ions are induced to undergo rapid uniform nucleation and sustained reversible stripping/plating with low energy barriers via the internally bridged shuttle channels. Paired with cyano group iron hexacyanoferrate (FeHCF) cathode, the FeHCF//MXene@Zn full battery delivers superior cycle durability and rate capability, whose service life with a CE of near 100% touches 850% of bare Zn powder counterparts. The proposed Ti₃C₂Tx MXene redistributor strategy concerning high-speed electrons/ions channel, low-barrier heterogeneous interface, is expected to be widely applied to other alkali metal anodes.

Top-Down Ultrasonication-Assisted Exfoliation for Prebonded Phosphorene-Graphene Heterostructures Enabling Fast Lithiation/Delithiation

We show a top-down synthesis approach to mass-produce phosphorene-graphene nanosheet composites with superior cycle stability and rate capability. Currently, using exfoliation to achieve two-dimensional (2D) materials is primarily limited to pure crystals. We discover that high-quality nanoscale 2D composite phosphorene-graphene sheets can be directly exfoliated from extremely low-cost bulk three-dimensional (3D) black phosphorus-graphite composites synthesized by mechanical milling while maintaining the chemical bonding and intimate electronic contact between 2D composite layers. The hybrid phosphorene-graphene material delivers high reversible capacities of 2030, 2003, and 1597 mAh/g at high current densities of 2, 4, and 6 A/g, respectively. Quantifying the dimensional electrochemical performance, we show that 2D phosphorene-graphene nanosheets not only have excellent electrochemical kinetics for fast lithium-ion diffusion and storage but also maintain the overall structural robustness of the entire electrode for long-term cyclability. This scalable synthesis paves the way for the practical application of phosphorene-graphene materials in batteries.

Manipulating anion intercalation enables a high-voltage aqueous dual ion battery

Aqueous graphite-based dual ion batteries have unique superiorities in stationary energy storage systems due to their non-transition metal configuration and safety properties. However, there is an absence of thorough study of the interactions between anions and water molecules and between anions and electrode materials, which is essential to achieve high output voltage. Here we reveal the four-stage intercalation process and energy conversion in a graphite cathode of anions with different configurations. The difference between the intercalation energy and hydration energy of bis(trifluoromethane)sulfonimide makes the best use of the electrochemical stability window of its electrolyte and delivers a high intercalation potential, while BF₄⁻ and CF₃SO₃⁻ do not exhibit a satisfactory potential because the graphite intercalation potential of BF₄⁻ is inferior and the graphite intercalation potential of CF₃SO₃⁻ exceeds the voltage window of its electrolyte. An aqueous dual ion battery based on the intercalation behaviors of bis(trifluoromethane)sulfonimide anions into a graphite cathode exhibits a high voltage of 2.2 V together with a specific energy of 242.74 Wh kg⁻¹. This work provides clear guidance for the voltage plateau manipulation of anion intercalation into two-dimensional materials.

The interactions between water molecules, electrode materials and anions are essential yet challenging for aqueous dual ion batteries. Here, the authors demonstrate the voltage manipulation of dual ion batteries through matching intercalation energy and solvation energy of different anions.

Recent Progress on the Alloy-Based Anode for Sodium-Ion Batteries and Potassium-Ion Batteries

High-energy batteries with low cost are urgently needed in the field of large-scale energy storage, such as grid systems and renewable energy sources. Sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) with alloy-based anodes provide huge potential due to their earth abundance, high capacity, and suitable working potential, and are recognized as attractive alternatives for next-generation batteries system. Although some important breakthroughs have been reported, more significant improvements are still required for long lifetime and high energy density. Herein, the latest progress for alloy-based anodes for SIBs and PIBs is summarized, mainly including Sn, Sb, Ge, Bi, Si, P, and their oxides, sulfides, selenides, and phosphides. Specifically, the material designs for the desired Na⁺ /K⁺ storage performance, phase transform, ionic/electronic transport kinetics, and specific chemical interactions are discussed. Typical structural features and research strategies of alloy-based anodes, which are used to facilitate processes in battery development for SIBs and PIBs, are also summarized. The perspective of future research of SIBs and PIBs is outlined.

Confining Aqueous Zn-Br Halide Redox Chemistry by Ti3C2TX MXene

With fluidity and dangerous corrosiveness, liquid insulating bromine elemental (Br₂) can hardly be confined by traditional conductive carriers (mainly carbon materials) for efficient redox without shuttle behavior. Thus, stationary Br₂-based energy storage devices are rarely advanced. Here, we introduce an electrochemical active parasite Br₂ to the Ti₃C₂T_XMXene host and construct an advanced aqueous zinc redox battery via a facile electrodeposition process (Br-Ti₃C₂T_X). Both ex situ experimental characterizations and density functional theory (DFT) simulations have validated the natural affinity between MXenes and Br species, which is manifested as their spontaneous fixation accompanied by rapid transfer of electrons in the interface region and interlayer confinement. Consequently, the battery delivers a high-voltage plateau at 1.75 V that contributes to an improved energy density of 259 Wh kg^-1_Br (144 Wh kg^-1_Br-Ti3C2TX), exhibiting efficient output capability in the high-voltage region. Besides, benefiting from enhanced redox kinetics, the capacity achieved at -15 °C approaches to 69% of the value at room temperature. More importantly, an excellent 10 000 cycles at -15 °C with negligible capacity decay is identified. The paradigm represents a step forward for developing stationary aqueous metal-Br₂ batteries.

Armoring Black Phosphorus Anode with Stable Metal-Organic-Framework Layer for Hybrid K-Ion Capacitors

Potassium-ion capacitors (KICs) are promising for sustainable and eco-friendly energy storage technologies, yet their slow reaction kinetics and poor cyclability induced by large K-ion size are a major obstacle toward practical applications. Herein, by employing black phosphorus nanosheets (BPNSs) as a typical high-capacity anode material, we report that BPNS anodes armored with an ultrathin oriented-grown metal-organic-framework (MOF) interphase layer (BPNS@MOF) exhibit regulated potassium storage behavior for high-performance KICs. The MOF interphase layers as protective layer with ordered pores and high chemical/mechanical stability facilitate K ion diffusion and accommodate the volume change of electrode, beneficial for improved reaction kinetics and enhanced cyclability, as evidenced by substantial characterizations, kinetics analysis and DFT calculations. Consequently, the BPNS@MOF electrode as KIC anodes exhibits outstanding cycle performance outperforming most of the reported state-of-art KICs so far.

Electrochemical Delamination of Ultralarge Few-Layer Black Phosphorus with a Hydrogen-Free Intercalation Mechanism

Due to strong interlayer interaction and ease of oxidation issues of black phosphorus (BP), the domain size of artificial synthesized few-layer black phosphorus (FL-BP) crystals is often below 10 µm, which extremely limits its further applications in large-area thin-film devices and integrated circuits. Herein, a hydrogen-free electrochemical delamination strategy through weak Lewis acid intercalation enabled exfoliation is developed to produce ultralarge FL-BP single-crystalline domains with high quality. The interaction between the weak Lewis acid tetra-n-butylammonium acetate (CH₃ COOTBA) and P atoms promotes the average domain size of FL-BP crystal up to 77.6 ± 15.0 µm and the largest domain size is found to be as large as 119 µm. The presence of H⁺ and H₂ O is found to sharply decrease the size of as-exfoliated FL-BP flakes. The electronic transport measurements show that the delaminated FL-BP crystals exhibit a high hole mobility of 76 cm² V^-1 s^-1 and an on/off ratio of 10³ at 298 K. A broadband photoresponse from 532 to 1850 nm with ultrahigh responsivity is achieved. This work provides a scalable, simple, and low-cost approach for large-area BP films that meet industrial requirements for nanodevices applications.

Stabilization of Black Phosphorus by Sonication-Assisted Simultaneous Exfoliation and Functionalization

Black phosphorus (BP) has extraordinary properties, but its ambient instability remains a critical challenge. Functionalization has been employed to overcome the sensitivity of BP to ambient conditions while preserving its properties. Herein, a simultaneous exfoliation-functionalization process is reported that functionalizes BP flakes during exfoliation and thus provides increased protection, which can be attributed to minimal exposure of the flakes to ambient oxygen and water. A tetrabutylammonium salt was employed for intercalation of BP, resulting in the formation of flakes with large lateral dimensions. The addition of an aryl iodide or an aryl iodonium salt to the exfoliation solvent creates a scalable strategy for the production of functionalized few-layer BP flakes. The ambient stability of functionalized BP was prolonged to a period of one week, as revealed by STEM, AFM, and X-ray photoelectron spectroscopy.

Advancing Applications of Black Phosphorus and BP-Analog Materials in Photo/Electrocatalysis through Structure Engineering and Surface Modulation

Black phosphorus (BP), an emerging 2D material semiconductor material, exhibits unique properties and promising application prospects for photo/electrocatalysis. However, the applications of BP in photo/electrocatalysis are hampered by the instability as well as low catalysis efficiency. Recently, tremendous efforts have been dedicated toward modulating its intrinsic structure, electronic property, and charge separation for enhanced photo/electrocatalytic performance through structure engineering. Simultaneously, the search for new substitute materials that are BP-analogous is ongoing. Herein, the latest theoretical and experimental progress made in the structural/surface engineering strategies and advanced applications of BP and BP-analog materials in relation to photo/electrocatalysis are extensively explored, and a presentation of the future opportunities and challenges of the materials is included at the end.

Two-Dimensional Black Phosphorus Nanomaterials: Emerging Advances in Electrochemical Energy Storage Science

Two-dimensional black phosphorus (2D BP), well known as phosphorene, has triggered tremendous attention since the first discovery in 2014. The unique puckered monolayer structure endows 2D BP intriguing properties, which facilitate its potential applications in various fields, such as catalyst, energy storage, sensor, etc. Owing to the large surface area, good electric conductivity, and high theoretical specific capacity, 2D BP has been widely studied as electrode materials and significantly enhanced the performance of energy storage devices. With the rapid development of energy storage devices based on 2D BP, a timely review on this topic is in demand to further extend the application of 2D BP in energy storage. In this review, recent advances in experimental and theoretical development of 2D BP are presented along with its structures, properties, and synthetic methods. Particularly, their emerging applications in electrochemical energy storage, including Li-/K-/Mg-/Na-ion, Li-S batteries, and supercapacitors, are systematically summarized with milestones as well as the challenges. Benefited from the fast-growing dynamic investigation of 2D BP, some possible improvements and constructive perspectives are provided to guide the design of 2D BP-based energy storage devices with high performance.

Unzipping of black phosphorus to form zigzag-phosphorene nanobelts

Phosphorene, monolayer or few-layer black phosphorus, exhibits fascinating anisotropic properties and shows interesting semiconducting behavior. The synthesis of phosphorene nanosheets is still a hot topic, including the shaping of its two-dimensional structure into nanoribbons or nanobelts. Here we report electrochemical unzipping of single crystalline black phosphorus into zigzag-phosphorene nanobelts, as well as nanosheets and quantum dots, via an oxygen-driven mechanism. The experimental results agree well with our theoretical calculations. The calculation for the unzipping mechanism study suggests that interstitial oxygen-pairs are the critical intermediate species for generating zigzag-phosphorene nanobelts. Although phosphorene oxidation has been reported, lengthwise cutting is hitherto unreported. Our discovery of phosphorene cut upon oxidation represents a previously unknown mechanism for the formation of various dimensions of phosphorene nanostructures, especially zigzag-phosphorene nanobelts. It opens up a way for studying the quantum effects and electronic properties of zigzag-phosphorene nanobelts.

Here, the authors demonstrate the electrochemical unzipping of single crystalline black phosphorus into zigzag-phosphorene nanobelts, nanosheets, and quantum dots, via a top-down oxygen-driven mechanism.

Red-phosphorus-impregnated carbon nanofibers for sodium-ion batteries and liquefaction of red phosphorus

Red phosphorus offers a high theoretical sodium capacity and has been considered as a candidate anode for sodium-ion batteries. Similar to silicon anodes for lithium-ion batteries, the electrochemical performance of red phosphorus is plagued by the large volume variation upon sodiation. Here we perform in situ transmission electron microscopy analysis of the synthesized red-phosphorus-impregnated carbon nanofibers with the corresponding chemo-mechanical simulation, revealing that, the sodiated red phosphorus becomes softened with a “liquid-like” mechanical behaviour and gains superior malleability and deformability against pulverization. The encapsulation strategy of the synthesized red-phosphorus-impregnated carbon nanofibers has been proven to be an effective method to minimize the side reactions of red phosphorus in sodium-ion batteries, demonstrating stable electrochemical cycling. Our study provides a valid guide towards high-performance red-phosphorus-based anodes for sodium-ion batteries.

Red phosphorus is a promising anode for Na-ion batteries but suffers from large volume change upon cycling. Here the authors show a red-phosphorus-impregnated carbon nanofiber design in which the sodiated red phosphorus is featured by a “liquid-like” behavior and ultra-stable electrochemical performance is realized.

Atomically thin PdSeO3 nanosheets: a promising 2D photocatalyst produced by quaternary ammonium intercalation and exfoliation

In 2018, the two-dimensional (2D) PdSeO₃ monolayer was predicted to be a highly promising photocatalyst for direct overall water splitting in the light of density functional theory (DFT) computations. Herein, we present the first report on the synthesis of 2D PdSeO₃ nanosheets by using the quaternary ammonium intercalation-assisted electrochemical exfoliation method. The resulting atomically thin PdSeO₃ nanosheets possess a moderate band gap with suitable band edge alignments for water splitting, and display excellent activity and stability in photocatalytic H₂ evolution.

Initiating Hexagonal MoO3 for Superb-Stable and Fast NH4 + Storage Based on Hydrogen Bond Chemistry

Nonmetallic ammonium (NH₄ ⁺ ) ions are applied as charge carriers for aqueous batteries, where hexagonal MoO₃ is initially investigated as an anode candidate for NH₄ ⁺ storage. From experimental and first-principle calculated results, the battery chemistry proceeds with reversible building-breaking behaviors of hydrogen bonds between NH₄ ⁺ and tunneled MoO₃ electrode frameworks, where the ammoniation/deammoniation mechanism is dominated by nondiffusion-controlled pseudocapacitive behavior. Outstanding electrochemical performance of MoO₃ for NH₄ ⁺ storage is delivered with 115 mAh g^-1 at 1 C and can retain 32 mAh g^-1 at 150 C. Furthermore, it remarkably exhibits ultralong and stable cyclic performance up to 100 000 cycle with 94% capacity retention and high power density of 4170 W kg^-1 at 150 C. When coupled with CuFe prussian blue analogous (PBA) cathode, the full ammonium battery can deliver decent energy density 21.3 Wh kg^-1 and the resultant flexible ammonium batteries at device level are also pioneeringly developed for potential realistic applications.

2 D Materials for Electrochemical Energy Storage: Design, Preparation, and Application

Electrochemical energy storage is a promising route to relieve the increasing energy and environment crises, owing to its high efficiency and environmentally friendly nature. However, it is still challenging to realize its widespread application because of unsatisfactory electrode materials, with either high cost or poor activity and new electrode materials are urgently needed. Two-dimensional (2 D) materials are possible candidates, owing to their unique geometry and physicochemical properties. This Review summarizes the latest advances in the development of 2 D materials for electrochemical energy storage. Computational investigation and design of 2 D materials are first introduced, and then preparation methods are presented in detail. Next, the application of such materials in supercapacitors, alkali metal-ion batteries, and metal-air batteries are summarized comprehensively. Finally, the challenges and perspectives are discussed to offer a guideline for future exploration of high-efficiency 2 D materials for electrochemical energy storage.

Recent Advances of Two-Dimensional (2 D) MXenes and Phosphorene for High-Performance Rechargeable Batteries

The design and development of advanced electrode materials for high-performance rechargeable batteries have been subjected to extensive studies. Very recently, two-dimensional (2 D) nanomaterials have become promising candidates for batteries, owing to their unique physicochemical properties. In particular, MXenes and phosphorene, which exhibit tailored electrical conductivity and ion storage capability, have attracted increasing attention. This Review presents a comprehensive summary of recent advances in the development of 2 D MXenes and phosphorene as electrode materials for high-performance batteries. Their physicochemical properties, including structural configurations and electronic properties of MXenes and direct band gap and anisotropic properties of phosphorene, are firstly discussed. Then, synthesis methods of the two materials are introduced. Thereafter, their applications as electrode materials in batteries, including lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), potassium-ion batteries (PIBs), lithium-sulfur (Li-S) batteries, and metal-air batteries, are summarized and discussed in detail. An emphasis is placed on analyzing performance enhancement mechanisms to elucidate fundamental understanding. Finally, future challenges and opportunities for MXenes and phosphorene as electrode materials for batteries are considered.

Metal-Organic Framework Derived CoS2 Wrapped with Nitrogen-Doped Carbon for Enhanced Lithium/Sodium Storage Performance

Transition metal sulfides are attractive electrode materials for both lithium-ion (LIBs) and sodium-ion batteries (SIBs). Starting from micron-sized Co(IPC)·H₂O (IPC: 4-(imidazole-1-yl) phthalic acid) and polydopamine as the metal-organic framework (MOF) precursor and carbon source, respectively, we produced a CoS₂/C/C composite constituting CoS₂ nanoparticles decorated with N-doped carbon layers and subjected to sulfurization. N-doped carbon layers provided a robust network for the CoS₂ nanoparticles, enhancing the structural integrity and electronic conductivity of the resulting CoS₂/C/C composite, which exhibited electrochemical performance superior to most existing CoS₂ composites, and was one of the best among all MOF derived CoS₂ anodes for LIBs and SIBs. The use of nanosized CoS₂ particles reduced the diffusion length for the transfer of Li⁺/Na⁺ ions, resulting in a high specific capacity at a higher current rate. N-doped carbon layers derived from the MOF precursor and polydopamine provided an electrically conductive network between the CoS₂ nanoparticles, thus preventing their aggregation and inhibiting adverse side reactions between the electrolyte and the surface of the electrode, and the high pseudocapacitive contribution resulted in the enhanced rate performance of the CoS₂/C/C electrodes.

Emerging 2D Materials Produced via Electrochemistry

2D materials are important building blocks for the upcoming generation of nanostructured electronics and multifunctional devices due to their distinct chemical and physical characteristics. To this end, large-scale production of 2D materials with high purity or with specific functionalities represents a key to advancing fundamental studies as well as industrial applications. Among the state-of-the-art synthetic protocols, electrochemical exfoliation of layered materials is a very promising approach that offers high yield, great efficiency, low cost, simple instrumentation, and excellent up-scalability. Remarkably, playing with electrochemical parameters not only enables tunable material properties but also increases the material diversities from graphene to a wide spectrum of 2D semiconductors. Here, a succinct and critical survey of the recent progress in this research direction is presented, comprising the strategic design, exfoliation principles, underlying mechanisms, processing techniques, and potential applications of 2D materials. At the end of the discussion, the emerging trends, challenges, and opportunities in real practice are also highlighted.

Facile Synthesis of FePS3 Nanosheets@MXene Composite as a High-Performance Anode Material for Sodium Storage

Searching for advanced anode materials with excellent electrochemical properties in sodium-ion battery is essential and imperative for next-generation energy storage system to solve the energy shortage problem. In this work, two-dimensional (2D) ultrathin FePS₃ nanosheets, a typical ternary metal phosphosulfide, are first prepared by ultrasonic exfoliation. The novel 2D/2D heterojunction of FePS₃ nanosheets@MXene composite is then successfully synthesized by in situ mixing ultrathin MXene nanosheets with FePS₃ nanosheets. The resultant FePS₃ nanosheets@MXene hybrids can increase the electronic conductivity and specific surface area, assuring excellent surface and interfacial charge transfer abilities. Furthermore, the unique heterojunction endows FePS₃ nanosheets@MXene composite to promote the diffusion of Na⁺ and alleviate the drastic change in volume in the cyclic process, enhancing the sodium storage capability. Consequently, the few-layered FePS₃ nanosheets uniformly coated by ultrathin MXene provide an exceptional reversible capacity of 676.1 mAh g^-1 at the current of 100 mA g^-1 after 90 cycles, which is equivalent to around 90.6% of the second-cycle capacity (746.4 mAh g^-1). This work provides an original protocol for constructing 2D/2D material and demonstrates the FePS₃@MXene composite as a potential anode material with excellent property for sodium-ion batteries.

Towards Antimonene and 2D Antimony Telluride through Electrochemical Exfoliation

Two-dimensional (2D) layered antimony (Sb) and antimony telluride (Sb₂ Te₃ ) are two valuable materials for optoelectronic devices and thermoelectric applications. Preparing high-quality sheets of these materials is the initial phase to promote their expected issues. Herein, micrometer-sized few-to-multilayered sheets of Sb and Sb₂ Te₃ have been obtained by electrochemical exfoliation. The layered rhombohedral Sb was exfoliated in Na₂ SO₄ and Li₂ SO₄ electrolytes by anodic-cationic intercalation, and Sb₂ Te₃ was exfoliated in Na₂ SO₄ . These findings are important contributions for the solution-based room-temperature electrochemical exfoliation, which is stable under glove-box-free conditions, to further improve the production of high-quality exfoliated sheets.

Non-aqueous solution-processed phosphorene by controlled low-potential electrochemical exfoliation and thin film preparation

Black phosphorus (BP) in its monolayer form called phosphorene is thought of as a successor of graphene and is of great interest for (opto)electronic applications. A quantitative and scalable method for the synthesis of (mono-)few-layer phosphorene has been an outstanding challenge due to the process irreproducibility and environmental degradation capability of the BP. Here, we report a facile controlled electrochemical exfoliation method for the preparation of a few-layer phosphorene (FP) with nearly 100% yield. Our approach relies on the low-potential influence in anhydrous and oxygen-free low-boiling acetonitrile (AN) and N,N-dimethylformamide (DMF) using alkylammonium ions. Herein, intercalation of positive ions into BP interlayers occurred with a minimum potential of -2.95 V in DMF and -2.85 V in AN and the non-damaging and highly accurate electrochemical exfoliation lasted at -3.8 V. A variety of analytical methods have revealed that in particular DMF-based exfoliation results in high-quality phosphorene of 1-5 layers with good crystallinity and lateral sizes up to tens of micrometers. Moreover, assurance of the oxygen- and water-free environment allowed us to minimize the surface oxidation of BP and, consequently, exfoliated phosphorene. We pioneer an effective and reproducible printing transfer of electrochemically exfoliated phosphorene films onto various flexible and rigid substrates. The surfactant-free process of exfoliation allowed assembly and transfer of thin films based on FP. The phosphorene-based films characterized as direct gap semiconductors have a layer-number-dependent bandgap with a tuning range larger than that of other 2D materials. We show that on varying the films' thickness, it is possible to modify their optical properties, which is a significant advantage for compact and switchable optoelectronic components.

Property-Activity Relationship of Black Phosphorus at the Nano-Bio Interface: From Molecules to Organisms

As a novel member of the two-dimensional nanomaterial family, mono- or few-layer black phosphorus (BP) with direct bandgap and high charge carrier mobility is promising in many applications such as microelectronic devices, photoelectronic devices, energy technologies, and catalysis agents. Due to its benign elemental composition (phosphorus), large surface area, electronic/photonic performances, and chemical/biological activities, BP has also demonstrated a great potential in biomedical applications including biosensing, photothermal/photodynamic therapies, controlled drug releases, and antibacterial uses. The nature of the BP-bio interface is comprised of dynamic contacts between nanomaterials (NMs) and biological systems, where BP and the biological system interact. The physicochemical interactions at the nano-bio interface play a critical role in the biological effects of NMs. In this review, we discuss the interface in the context of BP as a nanomaterial and its unique physicochemical properties that may affect its biological effects. Herein, we comprehensively reviewed the recent studies on the interactions between BP and biomolecules, cells, and animals and summarized various cellular responses, inflammatory/immunological effects, as well as other biological outcomes of BP depending on its own physical properties, exposure routes, and biodistribution. In addition, we also discussed the environmental behaviors and potential risks on environmental organisms of BP. Based on accumulating knowledge on the BP-bio interfaces, this review also summarizes various safer-by-design strategies to change the physicochemical properties including chemical stability and nano-bio interactions, which are critical in tuning the biological behaviors of BP. The better understanding of the biological activity of BP at BP-bio interfaces and corresponding methods to overcome the challenges would promote its future exploration in terms of bringing this new nanomaterial to practical applications.

Recent Advances in Chemical Functionalization of 2D Black Phosphorous Nanosheets

Owing to their tunable direct bandgap, high charge carrier mobility, and unique in-plane anisotropic structure, black phosphorus nanosheets (BPNSs) have emerged as one of the most important candidates among the 2D materials beyond graphene. However, the poor ambient stability of black phosphorus limits its practical application, due to the chemical degradation of phosphorus atoms to phosphorus oxides in the presence of oxygen and/or water. Chemical functionalization is demonstrated as an efficient approach to enhance the ambient stability of BPNSs. Herein, various covalent strategies including radical addition, nitrene addition, nucleophilic substitution, and metal coordination are summarized. In addition, efficient noncovalent functionalization methods such as van der Waals interactions, electrostatic interactions, and cation-π interactions are described in detail. Furthermore, the preparations, characterization, and diverse applications of functionalized BPNSs in various fields are recapped. The challenges faced and future directions for the chemical functionalization of BPNSs are also highlighted.