Nanoscaled Metal Borides and Phosphides: Recent Developments and Perspectives

Trace Ru Incorporation Boosted Co2P Nanorods for Superior Water Electrolysis and Substrate-Paired Electrolysis Toward Value-Added Chemicals in Alkaline Medium

Electro-valorization of biomass-derived chemicals has ensured sustainable production of value-added products, an effective approach for reducing carbon footprint, through renewable energy. Electrochemical oxidation and reduction reactions in aqueous media using H2O as a potential source for active hydrogenated and oxygenated species fulfill the purpose. In this study, Ru─Co2P nanorods are explored as a bifunctional electrocatalyst toward valorization of Organics at basic media. The in-situ electrogenerated Co3+ and Co4+ species act as active oxidants toward product selectivity. An overpotential of 68 mV is found for hydrogen evolution reaction (1 m NaOH) with Ru─Co2P. Further, used as cathode, Ru─Co2P effectively reduces furfuraldehyde to furfuryl alcohol and p-nitrophenol to p-aminophenol. Ru doping enables ease of formation of active species both for reduction and oxidation, faster charge transfer between catalyst to absorbates. Density Functional Theory calculation establishes Ru incorporation in Co2P surface results in enhanced adsorption of substrates. Ru doping modulates the electronic structure of Co2P which changes the density of states resulting in faster water dissociation and water splitting. To reach 10 mA cm-2 current density only 1.6 V is required for water electrolysis, whereas 1.4 V is enough for substrate-paired electrolysis with simultaneous oxidation of benzyl alcohol and reduction of p-nitro phenol.

Novel 2D Material of MBenes: Structures, Synthesis, Properties, and Applications in Energy Conversion and Storage

2D transition metal borides (MBenes) have garnered significant attention from researchers due to their exceptional electrical conductivity, strong mechanical rigidity, excellent dynamic and thermodynamic stability, which stimulates the enthusiasm of researchers for the study of MBenes. Over the past few years, extensive research efforts have been dedicated to the study of MBenes, resulting in a growing number of synthesis methods being developed. However, there remains a scarcity of comprehensive reviews on MBenes, particularly in relation to the synthesis techniques employed. To address this gap, this review aims to provide a comprehensive summary of the latest research findings on MBenes. An exhaustive exploration of the crystal structure types of MBenes is presented, highlighting the greater structural diversity compared to MXenes. Furthermore, a comprehensive review of the recent advancements in MBenes synthesis methodologies is provided. The review also delves into the physical and chemical properties of MBenes, while elucidating their applications in the realms of energy conversion and energy storage. Lastly, this review concludes by summarizing and offering insights on MBenes from three angles: synthesis, structure-property relationships, and application prospects.

Epitaxial Growth of 2D Binary Phosphides

Combinations of phosphorus with main group III, IV, and V elements are theoretically predicted to generate 2D binary phosphides with extraordinary properties and promising applications. However, experimental synthesis is significantly lacking. Here, a general approach for preparing 2D binary phosphides is reported using single crystalline surfaces containing the constituent element of target 2D materials as the substrate. To validate this, SnP3 and BiP, representing typical 2D binary phosphides, are successfully synthesized on Cu2Sn and bismuthene, respectively. Scanning tunneling microscopy imaging reveals a hexagonal pattern of SnP3 on Cu2Sn, while α-BiP can be epitaxially grown on the α-bismuthene domain on Cu2Sb. First-principles calculations reveal that the formation of SnP3 on Cu2Sn is associated with strong interface bonding and significant charge transfer, while α-BiP interacts weakly with α-bismuthene so that its semiconducting property is preserved. The study demonstrates an attractive avenue for the atomic-scale growth of binary 2D materials via substrate phase engineering.

A Robust Synthesis of Co2P and Ni2P Nanocatalysts from Hexaethylaminophosphine and Phosphine-Enhanced Phenylacetylene Hydrogenation

Metal-rich phases of general formula M2P have demonstrated interesting catalytic activity, e.g., for hydrogen evolution reaction and for hydrogenations in colloidal suspension. The production of well-crystallized nanoparticles of the M2P phase from commercial precursors on a large enough scale is not trivial as the existing routes generally require fairly high reaction temperatures and a large excess of the phosphorus source. Here, we selected a commercial aminophosphine, P(NEt2)3, as the phosphorus precursor (3 equiv or less) to develop a robust synthesis from CoCl2 (respectively NiCl2) that provided crystalline Co2P (respectively Ni2P) nanoparticles with high yields on a 9 mmol scale. Moreover, modification of the M2P nanoparticles via the addition of a molecular Lewis base is a promising route to trigger catalytic activity of the colloidal suspension at a lower temperature. For the hydrogenation of phenylacetylene catalyzed by Co2P and Ni2P nanoparticles, we showed that catalytic amounts of adequate phosphines, such as PnBu3 and also, in some instances, oleylamine, triggered a full conversion at lower temperatures than with the nanoparticles alone. We delineated the most efficient phosphines in the case of a Ni2P catalyst, using a stereoelectronic map of 13 phosphines.

Heterogeneous Ni-Boride/Phosphide Anchored Amorphous B-C Layer for Overall Water Electrocatalysis

The rational design of efficient and economical bifunctional electrocatalysts remained a challenge for overall water electrolysis. In this work, the Ni-boride/ phosphide particles anchored amorphous B-doped carbon layer with hierarchical porous characteristics in Ni foam (Ni3P/Ni3B/B-C/NF) was fabricated for overall water splitting. The Boroncarbide (B4C) power was filled and fixed in the NF interspace through the electroplating and electroless plating, and then annealed in vacuum high temperature. The amorphous B-C layer derived from the B4 C not only speeded up the electron transport, but also cooperate with Ni-boride/phosphide to enhance the electrocatalytic activity for HER and OER synergistically. Furthermore, the hierarchical porous architecture of Ni3P/Ni3B/B-C/NF increased space utilization to load more active materials. The self-supported Ni3P/Ni3B/B-C/NF electrode possessed a low overpotential of 212 and 280 mV to deliver 100 mA cm-2 for HER and OER, respectively, and high stability for 48 h. In particular, the electrolyzer constituted with the Ni3P/Ni3B/B-C/NF bifunctional electrocatalyst only required a voltage of 1.59 V at 50 mA cm-2 for water electrocatalysis under alkaline medium, and demonstrated long-term stability for 48 h. This study provides a new technical path for the development of bifunctional of transition metal borides to promote the application of hydrogen production from water splitting.

Enhanced Long-Term Stability of Crystalline Nickel-Boride (Ni23B6) Electrocatalyst by Encapsulation with Hexagonal Boron Nitride

Nickel boride catalysts show great potential as low-cost and efficient alternatives to noble-metal catalysts in acidic media; however, synthesizing and isolating a specific phase and composition of nickel boride is nontrivial, and issues persist in their long-term stability as electrocatalysts. Here, a single-crystal nickel boride, Ni23B6, is reported which exhibits high electrocatalytic activity for the hydrogen evolution reaction (HER) in an acidic solution, and that its poor long-term stability can be overcome via encapsulation by single-crystal trilayer hexagonal boron nitride (hBN) film. Interestingly, hBN-covered Ni23B6 on a Ni substrate shows an identical overpotential of 52 mV at a current density of 10 mA cm-2 to that of bare Ni23B6. This phenomenon indicates that the single-crystalline hBN layer is catalytically transparent and does not obstruct HER activation. The hBN/Ni23B6/Ni has remarkable long-term stability with negligible changes to its polarization curves for 2000 cycles, whereas the Ni23B6/Ni shows significant degradation after 650 cycles. Furthermore, chronoamperometric measurements indicate that stability is preserved for >20 h. Long-term stability tests also reveal that the surface morphology and chemical structure of the hBN/Ni23B6/Ni electrode remain preserved. This work provides a model for the practical design of robust and durable electrochemical catalysts through the use of hBN encapsulation.

Synergistic Manganese Cobalt Phosphide core-shell for the Electrochemical Detection of Methyl Parathion in Food Sample

The development of a robust electrocatalyst for the electrochemical sensor for hazardous pesticides will reduce its effects on the ecosystem. Herein, we synthesized the robust manganese cobalt phosphide (MnCoP) - Core-shell as an electrochemical sensor for the determination of hazardous pesticide methyl parathion (MP). The MnCoP- Core-shell was prepared with the sustainable self-template route can help with the larger surface area. The Core-shell structure of MnCoP possesses a higher active surface area which increases the electrocatalytic performance and is utilized to improve the electrochemical MP reduction with the synergism of the core and shell structure. Remarkably, it realizes the higher sensitivity (0.014 μA μM-1 cm-2) of MnCoP- Core-shell/GCE achieves towards MP with lower limit of detection (LoD 50 nM) and exceptional recovery rate of MP in vegetable samples are achieved with the differential pulse voltammetry (DPV) technique. The MnCoP- Core-shell electrode reserved their superior electrochemical performances with high reproducibility and repeatability. This prominent activity of the MnCoP core-shell towards the MP in real sample analysis, makes it a promising electrochemical sensor for the detection of MP.

Non-Noble-Metal-Based Electrocatalysts for Acidic Oxygen Evolution Reaction: Recent Progress, Challenges, and Perspectives

The oxygen evolution reaction (OER) plays a pivotal role in diverse renewable energy storage and conversion technologies, including water electrolysis, electrochemical CO2 reduction, nitrogen fixation, and metal-air batteries. Among various water electrolysis techniques, proton exchange membrane (PEM)-based water electrolysis devices offer numerous advantages, including high current densities, exceptional chemical stability, excellent proton conductivity, and high-purity H2. Nevertheless, the prohibitive cost associated with Ir/Ru-based OER electrocatalysts poses a significant barrier to the broad-scale application of PEM-based water splitting. Consequently, it is crucial to advance the development of non-noble metal OER catalysis substance with high acid-activity and stability, thereby fostering their widespread integration into PEM water electrolyzers (PEMWEs). In this review, a comprehensive analysis of the acidic OER mechanism, encompassing the adsorbate evolution mechanism (AEM), lattice oxygen mechanism (LOM) and oxide path mechanism (OPM) is offered. Subsequently, a systematic summary of recently reported noble-metal-free catalysts including transition metal-based, carbon-based and other types of catalysts is provided. Additionally, a comprehensive compilation of in situ/operando characterization techniques is provided, serving as invaluable tools for furnishing experimental evidence to comprehend the catalytic mechanism. Finally, the present challenges and future research directions concerning precious-metal-free acidic OER are comprehensively summarized and discussed in this review.

Cobalt-Based Nanoscale Material: An Emerging Electrocatalyst for Hydrogen Production

Modern civilization has been highly suffering from energy crisis and environmental pollutions. These two burning issues are directly and indirectly created from fossil fuel consumption and uncontrolled industrialization. The above critical issue can be solved through the proper utilization of green energy sources where no greenhouse gases will be generated upon burning of such materials. Hydrogen is the most eligible candidate for this purpose. Among various methods of hydrogen generation, electrocatalytic process is one of the most efficient methods because of easy handling and high efficiency. In these aspects Co-based nanomaterials are considered to be extremely significant as they can be utilized as efficient, recyclable and ideal catalytic system. In this article a series of Co-based nano-electrocatalysts has been discussed with proper structure-property relationship and their medium dependency. Therefore, such type of stimulating summary on recently reported electrocatalysts and their activity may be helpful for scientists of the corresponding field as well as for broader research communities. This can be inspiration for materials researchers to fabricate active catalysts for the production of hydrogen gas in room temperature.

Expedited Synthesis of Metal Phosphides Maximizes Dispersion, Air Stability, and Catalytic Performance in Selective Hydrogenation

Metal phosphides have been hailed as potential replacements for scarce noble metal catalysts in many aspects of the hydrogen economy from hydrogen evolution to selective hydrogenation reactions. But the need for dangerous and costly phosphorus precursors, limited support dispersion, and low stability of the metal phosphide surface toward oxidation substantially lower the appeal and performance of metal phosphides in catalysis. We show here that a 1-step procedure that relies on safe and cheap precursors can furnish an air-stable Ni2P/Al2O3 catalyst containing 3.2 nm nanoparticles. Ni2P/Al2O3 1-step is kinetically competitive with the palladium-based Lindlar catalyst in selective hydrogenation catalysis, and a loading corresponding to 4 ppm Ni was sufficient to convert 0.1 mol alkyne. The 1-step synthetic procedure alters the surface ligand speciation of Ni2P/Al2O3, which protects the nanoparticle surface from oxidation, and ensures that 85 % of the initial catalytic activity was retained after the catalyst was stored under air for 1.5 years. Preparation of Ni2P on a variety of supports (silica, TiO2, SBA-15, ZrO2, C and HAP) as well as Co2P/Al2O3, Co2P/TiO2 and bimetallic NiCoP/TiO2 demonstrates the generality with which supported metal phosphides can be accessed in a safe and straightforward fashion with small sizes and high dispersion.

Covalent Transition Metal Borosilicides: Reaction Pathways in Molten Salts for Water Oxidation Electrocatalysis

The properties of transition metal borides and silicides are intimately linked to the covalent character of the chemical bonds within their crystal structures. Bringing boron and silicon together within metal borosilicides can then engender different competing covalent networks and complex charge distributions. This situation results in unique structures and atomic environments, which can impact charge transport and catalytic properties. Metal borosilicides, however, hold the status of unusual exotic species, difficult to synthesize and with poor knowledge of their properties. Our strategy consists of developing a redox pathway to synthesize transition metal borosilicides in inorganic molten salts as high-temperature solvents. By studying the formation of Ni6Si2B, Co4.75Si2B, Fe5SiB2, and Mn5SiB2 with in situ X-ray diffraction, we highlight how new reaction routes, maintaining covalent structural building blocks, draw a general scheme of their formation. This pathway is driven by the covalence of the chemical bonds within the boron coordination framework. Next, we demonstrate high efficiency for water oxidation electrocatalysis, especially for Ni6Si2B. We ascribe the strongly increased resistance to corrosion, high stability, and electrocatalytic activity of the Ni6Si2B-derived material to three factors: (1) the two entangled boron and silicon covalent networks; (2) the ability to codope with boron and silicon an in situ generated catalytic layer; and (3) a rare electron enrichment of the transition metal by back-donation from boron atoms, previously unknown within this compound family. With this work, we then unveil a new chemical dimension for Earth-abundant water oxidation electrocatalysts by bringing to light a new family of materials.

Anionic Coordination Control in Building Cu-Based Electrocatalytic Materials for CO2 Reduction Reaction

Renewable energy-driven conversion of CO2 to value-added fuels and chemicals via electrochemical CO2 reduction reaction (CO2RR) technology is regarded as a promising strategy with substantial environmental and economic benefits to achieve carbon neutrality. Because of its sluggish kinetics and complex reaction paths, developing robust catalytic materials with exceptional selectivity to the targeted products is one of the core issues, especially for extensively concerned Cu-based materials. Manipulating Cu species by anionic coordination is identified as an effective way to improve electrocatalytic performance, in terms of modulating active sites and regulating structural reconstruction. This review elaborates on recent discoveries and progress of Cu-based CO2RR catalytic materials enhanced by anionic coordination control, regarding reaction paths, functional mechanisms, and roles of different non-metallic anions in catalysis. Finally, the review concludes with some personal insights and provides challenges and perspectives on the utilization of this strategy to build desirable electrocatalysts.

Unveiling the Roles of Alloyed Boron in Hexavalent Chromium Removal Using Borohydride-Synthesized Nanoscale Zerovalent Iron: Electron Donor and Antipassivator

Nanoscale zerovalent iron synthesized using borohydride (B-NZVI) has been widely applied in environmental remediation in recent decades. However, the contribution of boron in enhancing the inherent reactivity of B-NZVI and its effectiveness in removing hexavalent chromium [Cr(VI)] have not been well recognized and quantified. To the best of our knowledge, herein, a core-shell structure of B-NZVI featuring an Fe-B alloy shell beneath the iron oxide shell is demonstrated for the first time. Alloyed boron can reduce H+, contributing to more than 35.6% of H2 generation during acid digestion of B-NZVIs. In addition, alloyed B provides electrons for Fe3+ reduction during Cr(VI) removal, preventing in situ passivation of the reactive particle surface. Meanwhile, the amorphous oxide shell of B-NZVI exhibits an increased defect density, promoting the release of Fe2+ outside the shell to reduce Cr(VI), forming layer-structured precipitates and intense Fe-O bonds. Consequently, the surface-area-normalized capacity and surface reaction rate of B-NZVI are 6.5 and 6.9 times higher than those of crystalline NZVI, respectively. This study reveals the importance of alloyed B in Cr(VI) removal using B-NZVI and presents a comprehensive approach for investigating electron pathways and mechanisms involved in B-NZVIs for contaminant removal.

Recent Developments and Future Perspectives of Molybdenum Borides and MBenes

Metal borides have received a lot of attention recently as a potentially useful material for a wide range of applications. In particular, molybdenum-based borides and MBenes are of great significance, due to their remarkable properties like good electronic conductivity, considerable stability, high surface area, and environmental harmlessness. Therefore, in this article, the progress made in molybdenum-based borides and MBenes in recent years is reviewed. The first step in understanding these materials is to begin with an overview of their structural and electronic properties. Then synthetic technologies for the production of molybdenum borides, such as high-temperature/pressure methods, physical vapor deposition (PVD), chemical vapor deposition (CVD), element reaction route, molten salt-assisted, and selective etching methods are surveyed. Then, the critical performance of these materials in numerous applications like energy storage, catalysis, biosensors, biomedical devices, surface-enhanced Raman spectroscopy (SERS), and tribology and lubrication are summarized. The review concludes with an analysis of the current progress of these materials and provides perspectives for future research. Overall, this review will offer an insightful reference for the understanding molybdenum-based borides and their development in the future.

Molten-Salt Electrochemical Preparation of Co2B/MoB2 Heterostructured Nanoclusters for Boosted pH-Universal Hydrogen Evolution

Boosting the hydrogen evolution reaction (HER) activity of α-MoB2 at large current densities and in pH-universal medium is significant for efficient hydrogen production. In this work, Co2B/MoB2 heterostructured nanoclusters are prepared by molten-salt electrolysis (MSE) and then used as a HER catalyst. The composition, structure, and morphology of Co2B/MoB2 can be modulated by altering the stoichiometries of raw materials and synthesis temperatures. Impressively, the obtained Co2B/MoB2 at optimized conditions exhibits a low overpotential of 297 and 304 mV at 500 mA cm-2 in 0.5 m H2SO4 and 1 m KOH, respectively. Moreover, the Co2B/MoB2 catalyst possesses a long-term catalytic stability of over 190 h in both acidic and alkaline medium. The excellent HER performance is due to the modified electronic structure at the Co2B/MoB2 heterointerface where electrons are accumulated at the Mo sites to strengthen the H adsorption. Density functional theory (DFT) calculations reveal that the formation of the Co2B/MoB2 heterointerface decreases the H adsorption and H2O dissociation free energies, contributing to the boosted HER intrinsic catalytic activity of Co2B/MoB2. Overall, this work provides an experimental and theoretical paradigm for the design of efficient pH-universal boride heterostructure electrocatalysts.

Dehydrogenation of diborane on small Nbn+ clusters

The reactivity of Nbn+ (1 ≤ n ≤ 21) clusters with B2H6 is studied by using a self-developed multiple-ion laminar flow tube reactor combined with a triple quadrupole mass spectrometer (MIFT-TQMS). The Nbn+ clusters were generated by a magnetron sputtering source and reacted with the B2H6 gas under fully thermalized conditions in the downstream flow tube where the reaction time was accurately controlled and adjustable. The complete and partial dehydrogenation products NbnB1-4+ and NbnB1-4H1,2,4+ were detected, indicative of the removal of H2 and likely BHx moieties. Interestingly, these NbnB1-4+ and NbnB1-4H1,2,4+ products are limited to 3 ≤ n ≤ 6, suggesting that the small Nbn+ clusters are relatively more reactive than the larger Nbn>6+ clusters under the same conditions. By varying the B2H6 gas concentrations and the reactant doses introduced into the flow tube, and by changing the reaction time, we performed a detailed analysis of the reaction dynamics in combination with the DFT-calculated thermodynamics. It is demonstrated that the lack of cooperative active sites on the Nb1+ cations accounts for the weakened dehydrogenation efficiency. Nb2+ forms partial dehydrogenation products at a faster rate. In contrast, the Nbn>6+ clusters are subject to more flexible vibrational relaxation which disperse the energy gain of B2H6-adsorption and thus are unable to overcome the energy barriers for subsequent hydrogen atom transfer and H2 release.

Applications, prospects and challenges of metal borides in lithium sulfur batteries

Although the lithium-sulfur (Li-S) battery has a theoretical capacity of up to 1675 mA h g-1, its practical application is limited owing to some problems, such as the shuttle effect of soluble lithium polysulfides (LiPSs) and the growth of Li dendrites. It has been verified that some transition metal compounds exhibit strong polarity, good chemical adsorption and high electrocatalytic activities, which are beneficial for the rapid conversion of intermediate product in order to effectively inhibit the "shuttle effect". Remarkably, being different from other metal compounds, it is a significant characteristic that both metal and boron atoms of transition metal borides (TMBs) can bind to LiPSs, which have shown great potential in recent years. Here, for the first time, almost all existing studies on TMBs employed in Li-S cells are comprehensively summarized. We firstly clarify special structures and electronic features of metal borides to show their great potential, and then existing strategies to improve the electrochemical properties of TMBs are summarized and discussed in the focus sections, such as carbon-matrix construction, morphology control, heteroatomic doping, heterostructure formation, phase engineering, preparation techniques. Finally, the remaining challenges and perspectives are proposed to point out a direction for realizing high-energy and long-life Li-S batteries.

Multifunctional molybdenum-tuning porous nickel-cobalt bimetallic phosphide nanoarrays for efficient water splitting and energy-saving hydrogen production

The sluggish kinetics of the hydrogen evolution reaction (HER) and substantial barriers in the oxygen evolution reaction (OER) significantly impede its application in hydrogen production. To address this issue and enhance energy efficiency in hydrogen generation, we explored a high-activity alkaline HER catalyst while concurrently coupling it with the urea oxidation reaction (UOR). In this work, we designed and synthesized porous molybdenum (Mo)-modulated nickel-cobalt bimetallic phosphide nanoarrays (M0.3NCP@NF). This multifunctional self-supported electrocatalyst demonstrates superior performance in HER, OER, and UOR. The introduction of Mo, in the form of CoMoO4 nanoparticles, promotes interfacial electron transfer to reduce the electron density around the cations in phosphides, enhancing the kinetics and intrinsic activity. Furthermore, the morphological changes induced by Mo accelerate both electron and mass transfer processes. Density functional theory and operando electrochemical impedance spectroscopy indicate that Mo introduction optimizes the interaction with HER intermediate H*, facilitating the conversion to a high-valent active intermediate for OER and accelerating UOR kinetics. Benefiting from dual optimization of morphology and structure, the as-prepared M0.3NCP@NF electrocatalyst demonstrates outstanding HER, OER, and UOR performances. Notably, a full urea electrolysis device powered by M0.3NCP@NF operates with a cell voltage of only 1.53 V to achieve a current density of 100 mA cm-2. which is 240 mV lower than that of conventional water electrolysis, demonstrating the competitive potential of our approach for efficient and energy-saving hydrogen production, along with simultaneous urea wastewater remediation.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

Recent Progress of Transition Metal Compounds as Electrocatalysts for Electrocatalytic Water Splitting

Hydrogen has enormous commercial potential as a secondary energy source because of its high calorific value, clean combustion byproducts, and multiple production methods. Electrocatalytic water splitting is a viable alternative to the conventional methane steam reforming technique, as it operates under mild conditions, produces high-quality hydrogen, and has a sustainable production process that requires less energy. Electrocatalysts composed of precious metals like Pt, Au, Ru, and Ag are commonly used in the investigation of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Nevertheless, their limited availability and expensive cost restrict practical use. In contrast, electrocatalysts that do not contain precious metals are readily available, cost-effective, environmentally friendly, and possess electrocatalytic performance equal to that of noble metals. However, considerable research effort must be devoted to create cost-effective and high-performing catalysts. This article provides a comprehensive examination of the reaction mechanism involved in electrocatalytic water splitting in both acidic and basic environments. Additionally, recent breakthroughs in catalysts for both the hydrogen evolution and oxygen evolution reactions are also discussed. The structure-activity relationship of the catalyst was deep-going discussed, together with the prospects of current obstacles and potential for electrocatalytic water splitting, aiming at provide valuable perspectives for the advancement of economical and efficient electrocatalysts on an industrial scale.

Controlled Surface Modification of Cobalt Phosphide with Sulfur Tunes Hydrogenation Catalysis

Transition metal phosphides have shown promise as catalysts for water splitting and hydrotreating, especially when a small amount of sulfur is incorporated into the phosphides. However, the effect of sulfur on catalysis is not well understood. In part, this is because conventional preparation methods of sulfur-doped transition metal phosphides lead to sulfur both inside and at the surface of the material. Here, we present an alternative method of modifying cobalt phosphide (CoP) with sulfur using molecular S-transfer reagents, namely, phosphine sulfides (SPR3). SPR3 added sulfur to the surface of CoP and using a series of SPR3 reagents having different P═S bond strengths enabled control over the amount and type of sulfur transferred. Our results show that there is a distribution of different sulfur sites possible on the CoP surface with S-binding strengths in the range of 69 to 84 kcal/mol. This provides fundamental information on how sulfur binds to an amorphous CoP surface and provides a basis to assess how number and type of sulfur on CoP influences catalysis. For the catalytic hydrogenation of cinnamaldehyde, intermediate amounts of sulfur with intermediate binding strengths at the surface of CoP were optimal. With some but not too much sulfur, CoP exhibited a higher hydrogenation productivity and a decreased formation of secondary reaction products. Our work provides important insight into the S-effect on the catalysis by transition metal phosphides and opens new avenues for catalyst design.

Dually Sulphophilic Chromium Boride Nanocatalyst Boosting Sulfur Conversion Kinetics Toward High-Performance Lithium-Sulfur Batteries

The sluggish kinetics of sulfur conversions have long been hindering the implementation of fast and efficient sulfur electrochemistry in lithium-sulfur (Li-S) batteries. In this regard, herein the unique chromium boride (CrB) is developed via a well-confined mild-temperature thermal reaction to serve as an advanced sulfur electrocatalyst. Its interstitial-alloy nature features excellent conductivity, while the nano-lamination architecture affords abundant active sites for host-guest interactions. More importantly, the CrB nanocatalyst demonstrates a dual sulphophilicity with simultaneous Cr─S and B─S bondage for establishing strong interactions with the intermediate polysulfides. As a result, significant stabilization and promotion of sulfur redox behavior can be achieved, enabling an excellent Li-S cell cyclability with a minimum capacity fading rate of 0.0176% per cycle over 2000 cycles and a favorable rate capability up to 7 C. Additionally, a high areal capacity of 5.2 mAh cm-2 , and decent cycling and rate performances are still attainable under high sulfur loading and low electrolyte dosage. This work offers a facile approach and instructive insights into metal boride sulfur electrocatalyst, holding a good promise for pursuing high-efficiency sulfur electrochemistry and high-performance Li-S batteries.

Interesting influence of Al2O3 on the catalytic stability of Co2P, MoP and CoMoP catalysts for dry reforming of methane

Interestingly, the metal-support interaction (MSI) influence of different metal phosphides on catalytic stability might be different in dry reforming of methane (DRM). After being supported on Al2O3, there was a rise, decline and no change in the catalytic stability of CoMoP, MoP and Co2P, respectively. This was probably because the MSI can tune the structural stability, methane dissociation ability and oxidation resistance ability of metal phosphides, which were the key factors that determined their catalytic stability.

Iron phosphide nanocrystals as an air-stable heterogeneous catalyst for liquid-phase nitrile hydrogenation

Iron-based heterogeneous catalysts are ideal metal catalysts owing to their abundance and low-toxicity. However, conventional iron nanoparticle catalysts exhibit extremely low activity in liquid-phase reactions and lack air stability. Previous attempts to encapsulate iron nanoparticles in shell materials toward air stability improvement were offset by the low activity of the iron nanoparticles. To overcome the trade-off between activity and stability in conventional iron nanoparticle catalysts, we developed air-stable iron phosphide nanocrystal catalysts. The iron phosphide nanocrystal exhibits high activity for liquid-phase nitrile hydrogenation, whereas the conventional iron nanoparticles demonstrate no activity. Furthermore, the air stability of the iron phosphide nanocrystal allows facile immobilization on appropriate supports, wherein TiO2 enhances the activity. The resulting TiO2-supported iron phosphide nanocrystal successfully converts various nitriles to primary amines and demonstrates high reusability. The development of air-stable and active iron phosphide nanocrystal catalysts significantly expands the application scope of iron catalysts.

A Simple and Versatile Approach for the Low-Temperature Synthesis of Transition Metal Phosphide Nanoparticles from Metal Chloride Complexes and P(SiMe3 )3

Metal chloride complexes react with tris(trimethylsilyl)phosphine under mild condition to produce metal phosphide (TMP) nanoparticles (NPs), and chlorotrimethylsilane as a byproduct. The formation of Si-Cl bonds that are stronger than the starting M-Cl bonds acts as a driving force for the reaction. The potential of this strategy is illustrated through the preparation of ruthenium phosphide NPs using [RuCl2 (cymene)] and tris(trimethylsilyl)phosphine at 35 °C. Characterization with a combination of techniques including electron microscopy (EM), X-ray absorption spectroscopy (XAS), and solid-state nuclear magnetic resonance (NMR) spectroscopy, evidences the formation of small (diameter of 1.3 nm) and amorphous NPs with an overall Ru50 P50 composition. Interestingly, these NPs can be easily immobilized on functional support materials, which is of great interest for potential applications in catalysis and electrocatalysis. Mo50 P50 and Co50 P50 NPs can also be synthesized following the same strategy. This approach is simple and versatile and paves the way toward the preparation of a wide range of transition metal phosphide nanoparticles under mild reaction conditions.

Metallic CrP2 monolayer: potential applications in energy storage and conversion

Phosphorus-rich compounds have emerged as a promising class of energy storage and conversion materials due to their interesting structures and electrochemical properties. Herein, we propose that a metallic CrP2 monolayer, isomorphic to 1H-phase MoS2, is a good prospect as an anode for K-ion batteries and a catalyst for hydrogen evolution through first-principles calculations. The CrP2 monolayer demonstrates not only a desirable high K storage capacity (940 mA h g-1) but also a low K-ion diffusion barrier (0.10 eV) and average open circuit voltage (0.40 V). On the other hand, its Gibbs free energy (0.02 eV)/active site density is superior/comparable to that of commercial Pt, resulting from the contribution of the lone pair electrons of the P atom. Its high structural stability and intrinsic metallicity can ensure high safety and performance during the cyclic process. These interesting properties make the CrP2 monolayer a promising multifunctional material for energy storage and conversion devices.

Colloidal semiconductor nanocrystals: from bottom-up nanoarchitectonics to energy harvesting applications

Colloidal semiconductor nanocrystals (NCs) have been extensively investigated owing to their unique properties induced by the quantum confinement effect. The advent of colloidal synthesis routes led to the design of stable colloidal NCs with uniform size, shape, and composition. Metal oxides, phosphides, and chalcogenides (ZnE, CdE, PbE, where E = S, Se, or Te) are few of the most important monocomponent semiconductor NCs, which show excellent optoelectronic properties. The ability to build quantum confined heterostructures comprising two or more semiconductor NCs offer greater customization and tunability of properties compared to their monocomponent counterparts. More recently, the halide perovskite NCs showed exceptional optoelectronic properties for energy generation and harvesting applications. Numerous applications including photovoltaic, photodetectors, light emitting devices, catalysis, photochemical devices, and solar driven fuel cells have demonstrated using these NCs in the recent past. Overall, semiconductor NCs prepared via the colloidal synthesis route offer immense potential to become an alternative to the presently available device applications. This feature article will explore the progress of NCs syntheses with outstanding potential to control the shape and spatial dimensionality required for photovoltaic, light emitting diode, and photocatalytic applications. We also attempt to address the challenges associated with achieving high efficiency devices with the NCs and possible solutions including interface engineering, packing control, encapsulation chemistry, and device architecture engineering.

Nano-metal diborides-supported anode catalyst with strongly coupled TaOx/IrO2 catalytic layer for low-iridium-loading proton exchange membrane electrolyzer

The sluggish kinetics of oxygen evolution reaction (OER) and high iridium loading in catalyst coated membrane (CCM) are the key challenges for practical proton exchange membrane water electrolyzer (PEMWE). Herein, we demonstrate high-surface-area nano-metal diborides as promising supports of iridium-based OER nanocatalysts for realizing efficient, low-iridium-loading PEMWE. Nano-metal diborides are prepared by a novel disulphide-to-diboride transition route, in which the entropy contribution to the Gibbs free energy by generation of gaseous sulfur-containing products plays a crucial role. The nano-metal diborides, TaB2 in particular, are investigated as the support of IrO2 nanocatalysts, which finally forms a TaOx/IrO2 heterojunction catalytic layer on TaB2 surface. Multiple advantageous properties are achieved simultaneously by the resulting composite material (denoted as IrO2@TaB2), including high electrical conductivity, improved iridium mass activity and enhanced corrosion resistance. As a consequence, the IrO2@TaB2 can be used to fabricate the membrane electrode with a low iridium loading of 0.15 mg cm-2, and to give an excellent catalytic performance (3.06 A cm-2@2.0 V@80 oC) in PEMWE-the one that is usually inaccessible by unsupported Ir-based nanocatalysts and the vast majority of existing supported Ir-based catalysts at such a low iridium loading.

Strain and Surface Engineering of Multicomponent Metallic Nanomaterials with Unconventional Phases

Multicomponent metallic nanomaterials with unconventional phases show great prospects in electrochemical energy storage and conversion, owing to unique crystal structures and abundant structural effects. In this review, we emphasize the progress in the strain and surface engineering of these novel nanomaterials. We start with a brief introduction of the structural configurations of these materials, based on the interaction types between the components. Next, the fundamentals of strain, strain effect in relevant metallic nanomaterials with unconventional phases, and their formation mechanisms are discussed. Then the progress in surface engineering of these multicomponent metallic nanomaterials is demonstrated from the aspects of morphology control, crystallinity control, surface modification, and surface reconstruction. Moreover, the applications of the strain- and surface-engineered unconventional nanomaterials mainly in electrocatalysis are also introduced, where in addition to the catalytic performance, the structure-performance correlations are highlighted. Finally, the challenges and opportunities in this promising field are prospected.

Au Nanoparticles Decorated CoP Nanowire Array: A Highly Sensitive, Anticorrosive, and Recyclable Surface-Enhanced Raman Scattering Substrate

Metal-semiconductor composites are promising candidates for surface-enhanced Raman scattering (SERS) substrates, but their inert basal plane, poor active sites, and limited stability hamper their commercial prospects. Herein, we report a three-dimensional CoP nanowire array decorated with Au nanoparticles on carbon cloth (Au@CoP/CC) as a self-supporting flexible SERS substrate. The Au nanoparticles spontaneously grew on the surface of the CoP nanowire array to form efficient SERS hot spots by a redox reaction with HAuCl₄ without any additional reducing agents. Such Au@CoP/CC substrate exhibited a limit of detection of 10^-11 M using rhodamine 6G as a model dye with outstanding corrosion resistance ability even under extreme acid and alkali conditions, which is better than many recently reported Au-based SERS substrates. Finite-difference time-domain simulation results demonstrated that Au@CoP/CC can provide a high density of regions with intense local electric field enhancement. Moreover, Au@CoP/CC can degrade target organic dyes for the self-cleaning and reproduction of SERS-active substrates under visible light irradiation. This work provides a novel means of using the plasmonic metal-transition metal phosphide composites for high-performance SERS sensing and photodegradation.

Monolayer molybdenum diborides containing flat and buckled boride layers as anode materials for lithium-ion batteries

The materials community is interested in discovering new two-dimensional (2D) crystals because of the potential for fascinating features. In this work, by employing a systematic first-principles DFT analysis and MD simulations, we investigated the potential applications of monolayer Mo borides containing flat and buckled boride rings named P6/mmm and R3̄m MoB₂ as anode materials of lithium-ion batteries. Our preliminary investigations show that the MoB₂ monolayers possess significant structural, thermodynamic, mechanical, and dynamical stability. Due to their distinctive crystal structures, the Mo borides exhibit unique electronic properties, as expected. Additionally, we discovered that the highly negative Li adsorption energy achieved can aid in stabilizing the Li's adsorption on the surface of MoB₂ rather than clustering, which ensured its suitability for LIB anode applications. The low computed Li-ion and Li-vacancy migration energy barrier provides robust charge/discharge performance even at a fully lithiated state, signifying their extraordinary possibility of being a suitable anode material for Li batteries. Both the monolayers can hold a maximum of two layers of Li ions on both sides to give a huge specific capacity of 912 mA h g^-1, much higher than graphene and MoS₂-based anodes. The computed in-plane stiffness constants demonstrate that the monolayer pristine and lithiated MoB₂ satisfies Born's criteria, implying its mechanical flexibility. Additionally, its strong mechanical and thermal properties at the pristine and the lithiated state indicate that the 2D MoB₂ can withstand massive volume expansion at a high temperature of 500 K during the lithiation/de-lithiation reaction and is remarkably beneficial for manufacturing flexible anodes. Based on the above findings, these two newly designed classes of monolayers of MoB₂ are anticipated to open a new avenue for the upcoming generation of lithium-ion batteries.

Metal-organic framework-mediated construction of confined ultrafine nickel phosphide immobilized in reduced graphene oxide with excellent cycle stability for asymmetric supercapacitors

Transition metal phosphides (TMPs) with unique metalloid features have been promised great application potential in developing high-efficiency electrode materials for electrochemical energy storage. Nevertheless, sluggish ion transportation and poor cycling stability are the critical hurdles limiting their application prospects. Herein, we presented the metal-organic framework-mediated construction of ultrafine Ni₂P immobilized in reduced graphene oxide (rGO). Nano-porous two-dimensional (2D) Ni-metal-organic framework (Ni-MOF) was grown on holey graphene oxide (Ni(BDC)-HGO), followed by MOF-mediated tandem pyrolysis (carbonization and phosphidation; Ni(BDC)-HGO-X-P, X denoted carbonization temperature and P represented phosphidation). Structural analysis revealed that the open-framework structure in Ni(BDC)-HGO-X-Ps had endowed them with excellent ion conductivity. The Ni₂P wrapped by carbon shells and the PO bonds linking between Ni₂P and rGO ensured the better structural stability of Ni(BDC)-HGO-X-Ps. The resulting Ni(BDC)-HGO-400-P delivered a capacitance of 2333.3 F g^-1 at 1 A g^-1 in a 6 M KOH aqueous electrolyte. More importantly, Ni(BDC)-HGO-400-P//activated carbon, the assembled asymmetric supercapacitor with an energy density of 64.5 Wh kg^-1 and a power density of 31.7 kW kg^-1, almost maintained its initial capacitance after 10,000 cycles. Furthermore, in situ electrochemical-Raman measurements were exploited to demonstrate the electrochemical changes of Ni(BDC)-HGO-400-P throughout the charging and discharging processes. This study has further shed light on the design rationality of TMPs for optimizing supercapacitor performance.

Rhenium-Based Electrocatalysts for Water Splitting

Due to the contamination and global warming problems, it is necessary to search for alternative environmentally friendly energy sources. In this area, hydrogen is a promising alternative. Hydrogen is even more promising, when it is obtained through water electrolysis operated with renewable energy sources. Among the possible devices to perform electrolysis, proton exchange membrane (PEM) electrolyzers appear as the most promising commercial systems for hydrogen production in the coming years. However, their massification is affected by the noble metals used as electrocatalysts in their electrodes, with high commercial value: Pt at the cathode where the hydrogen evolution reaction occurs (HER) and Ru/Ir at the anode where the oxygen evolution reaction (OER) happens. Therefore, to take full advantage of the PEM technology for green H2 production and build up a mature PEM market, it is imperative to search for more abundant, cheaper, and stable catalysts, reaching the highest possible activities at the lowest overpotential with the longest stability under the harsh acidic conditions of a PEM. In the search for new electrocatalysts and considering the predictions of a Trasatti volcano plot, rhenium appears to be a promising candidate for HER in acidic media. At the same time, recent studies provide evidence of its potential as an OER catalyst. However, some of these reports have focused on chemical and photochemical water splitting and have not always considered acidic media. This review summarizes rhenium-based electrocatalysts for water splitting under acidic conditions: i.e., potential candidates as cathode materials. In the various sections, we review the mechanism concepts of electrocatalysis, evaluation methods, and the different rhenium-based materials applied for the HER in acidic media. As rhenium is less common for the OER, we included a section about its use in chemical and photochemical water oxidation and as an electrocatalyst under basic conditions. Finally, concluding remarks and perspectives are given about rhenium for water splitting.

Synthesis of Ni-B Compounds by High-Pressure and High-Temperature Method

Nickel borides are promising multifunctional materials for high hardness and excellent properties in catalysis and magnetism. However, it is still a blank of intrinsic properties in Ni-B compounds, because crystallization of the single phases of Ni-B compounds with micro-size is a challenge. In this work, single phases of Ni₂B (I4/mcm), α-Ni₄B₃ (Pnma), β-Ni₄B₃ (C2/c), and NiB (Cmcm) are synthesized by high pressure and high temperature (HPHT). The results indicate that synthesizing α-Ni₄B₃ and β-Ni₄B₃ requires more energy than Ni₂B and NiB. The growth process of Ni-B compounds is that Ni covers B to form Ni-B compounds under HPHT, which also makes the slight excess of B necessary. So, generating homogeneous distribution of starting materials and increasing the interdiffusion between Ni and B are two keys to synthesize well crystallized and purer samples by HPHT. This work uncovers the growth process of Ni-B compounds, which is significant to guide the synthesis of highly crystalline transition metal borides (TMBs) in the future.

Tunable Synthesis of Metal-Rich and Phosphorus-Rich Nickel Phosphides and Their Comparative Evaluation as Hydrogen Evolution Electrocatalysts

Flexible synthetic routes to crystalline metal-rich to phosphorus-rich nickel phosphides are highly desired for comparable electrocatalytic HER studies. This report details solvent-free, direct, and tin-flux-assisted synthesis of five different nickel phosphides from NiCl₂ and phosphorus at moderate temperatures (500 °C). Direct reactions are thermodynamically driven via PCl₃ formation and tuned through reaction stoichiometry to produce crystalline Ni-P materials from metal-rich (Ni₂P, Ni₅P₄) to phosphorus-rich (cubic NiP₂) compositions. A tin flux in NiCl₂/P reactions allows access to monoclinic NiP₂ and NiP₃. Intermediates in tin flux reactions were isolated to help identify phosphorus-rich Ni-P formation mechanisms. These crystalline micrometer-sized nickel phosphide powders were affixed to carbon-wax electrodes and investigated as HER electrocatalysts in acidic electrolyte. All nickel phosphides show moderate HER activity in a potential range of -160 to -260 mV to achieve current densities of 10 mA/cm² ordered as c-NiP₂ ≥ Ni₅P₄ > NiP₃ > m-NiP₂ > Ni₂P, with NiP₃ activity showing some particle size influence. Phosphorus-rich c/m-NiP₂ appears most stable under acidic conditions during extended reactions. The HER activity of these different nickel phosphides appears influenced by a combination of factors such as particle size, phosphorus content, polyphosphide anions, and surface charge.

Tailored Heterojunction Active Sites for Oxygen Electrocatalyst Promotion in Zinc-Air Batteries

Rechargeable zinc-air batteries (ZABs) are promising energy storage systems due to their low-cost and safety. However, the working principle of ZABs is based on oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which display sluggish kinetic and low stability. Herein, this work proposes a novel method to design a heterogeneous CoP/CoO electrocatalyst on mesopore nanobox carbon/carbon nanotube (CoP/CoO@MNC-CNT) that enriched active sites and synergistic effect. Moreover, the well-defined heterointerfaces could lower the energy barrier for intermediate species adsorption and promote OER and ORR electrochemical performances. The CoP/CoO@MNC-CNT electrocatalyst presents a high half-wave potential of 0.838 V for ORR and a small overpotential of 270 mV for OER. The ZABs-based CoP/CoO@MNC-CNT air-cathode shows an open-circuit voltage of 1.409 V, the long-term cycle life of 500 h with a small voltage difference change of 7.7%. Additionally, the flexible ZABs exhibit highly mechanical stability, demonstrating their application potential in wearable electronic devices.

Transition Metal Phosphide Nanoarchitectonics for Versatile Organic Catalysis

Transition metal phosphides (TMP) posses unique physiochemical, geometrical, and electronic properties, which can be exploited for different catalytic applications, such as photocatalysis, electrocatalysis, organic catalysis, etc. Among others, the use of TMP for organic catalysis is less explored and still facing many complex challenges, which necessitate the development of sustainable catalytic reaction protocols demonstrating high selectivity and yield of the desired molecules of high significance. In this regard, the controlled synthesis of TMP-based catalysts and thorough investigations of underlying reaction mechanisms can provide deeper insights toward practical achievement of desired applications. This review aims at providing a comprehensive analysis on the recent advancements in the synthetic strategies for the tailored and tunable engineering of structural, geometrical, and electronic properties of TMP. In addition, their unprecedented catalytic potential toward different organic transformation reactions is succinctly summarized and critically analyzed. Finally, a rational perspective on future opportunities and challenges in the emerging field of organic catalysis is provided. On the account of the recent achievements accomplished in organic synthesis using TMP, it is highly anticipated that the use of TMP combined with advanced innovative technologies and methodologies can pave the way toward large scale realization of organic catalysis.

Bonding, Thermodynamics, and Spectroscopy of the Metal Borides UB0/+/- and WB0/+/

The bonding and spectroscopy of the UB^0/+/- and WB^0/+/- molecules were examined by performing high-level electronic structure calculation on their low-lying electronic states. The calculations were performed at the SO-CASPT2 level to obtain the low-lying excited states and at the FPD level to calculate the adiabatic electronic affinities (AEA), ionization energies (IE), and bond dissociation energies (BDE). Compared to UC and UN, UB has a much denser manifold of states below 1.7 eV. The ground state of UB is predicted to be ⁸I_5/2, and that of WB is ⁶Π_7/2. The calculated IEs of UB and WB are 6.241 and 7.314 eV, respectively, and the corresponding AEAs are 1.160 and 1.422 eV. The BDE of UB is predicted to be 223.1 kJ/mol, which is considerably lower than those predicted for UC and UN and ∼35 kJ/mol lower than the BDE of WB. NBO calculations show that the U and B are connected by two 1-electron π bonds and one 1-electron σ bond with substantial ionic character and a bond order of 1.5. There are three unpaired electrons in the 5f on U. WB has less ionic character than UB with a doubly occupied π bond and a singly occupied σ bond for a bond order of ∼1.5. The results show that the U in UB behaves more like an actinide and the W in WB more like a transition metal.

A copper nitride nanocube catalyst for highly efficient hydroboration of alkynes

The hydroboration of alkynes with bis(pinacolato)diboron is a useful method for the synthesis of vinyl boronate esters, which are essential intermediates in organic syntheses. Copper catalysts have been used extensively in these reactions. However, previously reported Cu-catalyst systems inevitably require additives and elevated temperatures. Herein, we report, for the first time, a simple and efficient hydroboration of alkynes under additive-free and mild reaction conditions (i.e., at a temperature of 30 °C) using a copper nitride nanocube (Cu₃N NC) catalyst. A wide range of alkynes can be transformed into their corresponding boronate esters. Cu₃N NCs are also applicable in the hydroboration of alkynes with tetrahydroxydiboron to synthesize vinyl boronic acids. Moreover, the Cu₃N NCs were easily separated by simple filtration and could be reused several times without any loss of their original activity. Hence, these highly active and reusable Cu₃N NC catalysts offer an environmentally friendly route for the efficient production of vinyl boronates.

Interface Engineering Toward Expedited Li2 S Deposition in Lithium-Sulfur Batteries: A Critical Review

Lithium-sulfur batteries (LSBs) with superior energy density are among the most promising candidates of next-generation energy storage techniques. As the key step contributing to 75% of the overall capacity, Li₂ S deposition remains a formidable challenge for LSBs applications because of its sluggish kinetics. The severe kinetic issue originates from the huge interfacial impedances, indicative of the interface-dominated nature of Li₂ S deposition. Accordingly, increasing efforts have been devoted to interface engineering for efficient Li₂ S deposition, which has attained inspiring success to date. However, a systematic overview and in-depth understanding of this critical field are still absent. In this review, the principles of interface-controlled Li₂ S precipitation are presented, clarifying the pivotal roles of electrolyte-substrate and electrolyte-Li₂ S interfaces in regulating Li₂ S depositing behavior. For the optimization of the electrolyte-substrate interface, efforts on the design of substrates including metal compounds, functionalized carbons, and organic compounds are systematically summarized. Regarding the regulation of electrolyte-Li₂ S interface, the progress of applying polysulfides catholytes, redox mediators, and high-donicity/polarity electrolytes is overviewed in detail. Finally, the challenges and possible solutions aiming at optimizing Li₂ S deposition are given for further development of practical LSBs. This review would inspire more insightful works and, more importantly, may enlighten other electrochemical areas concerning heterogeneous deposition processes.

Achieving High Performance Electrode for Energy Storage with Advanced Prussian Blue-Drived Nanocomposites-A Review

Recently, Prussian blue analogues (PBAs)-based anode materials (oxides, sulfides, selenides, phosphides, borides, and carbides) have been extensively investigated in the field of energy conversion and storage. This is due to PBAs' unique properties, including high theoretical specific capacity, environmental friendly, and low cost. We thoroughly discussed the formation of PBAs in conjunction with other materials. The performance of composite materials improves the electrochemical performance of its energy storage materials. Furthermore, new insights are provided for the manufacture of low-cost, high-capacity, and long-life battery materials in order to solve the difficulties in different electrode materials, combined with advanced manufacturing technology and principles. Finally, PBAs and their composites' future challenges and opportunities are discussed.

Introducing Porosity into Refractory Molybdenum Boride through Controlled Decomposition of a Metastable Mo-Al-B Precursor

The high temperatures typically required to synthesize refractory compounds preclude the formation of high-energy morphological features, including nanoscopic pores that are beneficial for applications, such as catalysis, that require higher surface areas. Here, we demonstrate a low-temperature multistep pathway to engineer mesoporosity into a catalytic refractory material. Mesoporous molybdenum boride, α-MoB, forms through the controlled thermal decomposition of nanolaminate-containing sheets of the metastable MAB (metal-aluminum-boron) phase Mo₂AlB₂ and amorphous alumina. Upon heating, the Mo₂AlB₂ layers of the Mo₂AlB₂-AlO_x nanolaminate, which is derived from MoAlB, begin to bridge and decompose, forming inclusions of alumina in a framework of α-MoB. The alumina can be dissolved in aqueous sodium hydroxide in an autoclave, forming α-MoB with empty and accessible pores. Statistical analysis of the morphologies and dimensions of the pores reveals a correlation with grain size, which relates to the pathway by which the alumina inclusions form. The transformation of Mo₂AlB₂ to α-MoB is topotactic due to crystal structure relationships, resulting in a high density of stacking faults that can be modeled to account for the observed experimental diffraction data. Porosity was validated by comparing surface areas and demonstrating catalytic viability for the hydrogen evolution reaction.