Magnesium Hydride Nanoparticles Self-Assembled on Graphene as Anode Material for High-Performance Lithium-Ion Batteries

An Ultra-Stable Electrode-Solid Electrolyte Composite for High-Performance All-Solid-State Li-Ion Batteries

The low ionic and electronic conductivity between current solid electrolytes and high-capacity anodes limits the long-term cycling performance of all-solid-state lithium-ion batteries (ASSLIBs). Herein, this work reports the fabrication of an ultra-stable electrode-solid electrolyte composite for high-performance ASSLIBs enabled by the homogeneous coverage of ultrathin Mg(BH₄ )₂ layers on the surface of each MgH₂ nanoparticle that are uniformly distributed on graphene. The initial discharge process of Mg(BH₄ )₂ layers results in uniform coverage of MgH₂ nanoparticle with both LiBH₄ as the solid electrolyte and Li₂ B₆ with even higher Li ion conductivity than LiBH₄ . Consequently, the Li ion conductivity of graphene-supported MgH₂ nanoparticles covered with ultrathin Mg(BH₄ )₂ layers is two orders of magnitude higher than that without Mg(BH₄ )₂ layers. Moreover, the thus-formed inactive Li₂ B₆ with strong adsorption capability toward LiBH₄ , acts as a stabilizing framework, which, coupled with the structural support role of graphene, alleviates the volume change of MgH₂ nanoparticles and facilitates the intimate contact between LiBH₄ and individual MgH₂ nanoparticles, leading to the formation of uniform stable interfaces with high ionic and electronic conductivity on each MgH₂ nanoparticles. Hence, an ultrahigh specific capacity of 800 mAh g^-1 is achieved for MgH₂ at 2 A g^-1 after 350 cycles.

Graphene-Modified Co-B-P Catalysts for Hydrogen Generation from Sodium Borohydride Hydrolysis

Sodium borohydride (NaBH₄) is considered a good candidate for hydrogen generation from hydrolysis because of its high hydrogen storage capacity (10.8 wt%) and environmentally friendly hydrolysis products. However, due to its sluggish hydrogen generation (HG) rate in the water, it usually needs an efficient catalyst to enhance the HG rate. In this work, graphene oxide (GO)-modified Co-B-P catalysts were obtained using a chemical in situ reduction method. The structure and composition of the as-prepared catalysts were characterized, and the catalytic performance for NaBH₄ hydrolysis was measured as well. The results show that the as-prepared catalyst with a GO content of 75 mg (Co-B-P/75rGO) exhibited an optimal catalytic efficiency with an HG rate of 12087.8 mL min^-1 g^-1 at 25 °C, far better than majority of the findings that have been reported. The catalyst had a good stability with 88.9% of the initial catalytic efficiency following 10 cycles. In addition, Co-, B-, and P-modified graphene showed a synergistic effect improving the kinetics and thermodynamics of NaBH₄ hydrolysis with a lower activation energy of 28.64 kJ mol^-1. These results reveal that the GO-modified Co-B-P catalyst has good potential for borohydride hydrolysis applications.

Recent Development in Nanoconfined Hydrides for Energy Storage

Hydrogen is the ultimate vector for a carbon-free, sustainable green-energy. While being the most promising candidate to serve this purpose, hydrogen inherits a series of characteristics making it particularly difficult to handle, store, transport and use in a safe manner. The researchers’ attention has thus shifted to storing hydrogen in its more manageable forms: the light metal hydrides and related derivatives (ammonia-borane, tetrahydridoborates/borohydrides, tetrahydridoaluminates/alanates or reactive hydride composites). Even then, the thermodynamic and kinetic behavior faces either too high energy barriers or sluggish kinetics (or both), and an efficient tool to overcome these issues is through nanoconfinement. Nanoconfined energy storage materials are the current state-of-the-art approach regarding hydrogen storage field, and the current review aims to summarize the most recent progress in this intriguing field. The latest reviews concerning H₂ production and storage are discussed, and the shift from bulk to nanomaterials is described in the context of physical and chemical aspects of nanoconfinement effects in the obtained nanocomposites. The types of hosts used for hydrogen materials are divided in classes of substances, the mean of hydride inclusion in said hosts and the classes of hydrogen storage materials are presented with their most recent trends and future prospects.

Metal Hydrides with In Situ Built Electron/Ion Dual-Conductive Framework for Stable All-Solid-State Li-Ion Batteries

Due to their high theoretical specific capacity, metal hydrides are considered to be one of the most promising anode material for all-solid-state Li-ion batteries. Their practical application suffers, however, from the poor cycling stability and sluggish kinetics. Herein, we report the in situ fabrication of MgH₂ and Mg₂NiH₄ that are uniformly space-confined by inactive Nd₂H₅ frameworks with high Li-ion and electron conductivity through facile hydrogenation of single-phase Nd₄Mg₈₀Ni₈ alloys. The formation of MgH₂ and Mg₂NiH₄ nanocrystals could not only shorten Li-ion and electron diffusion pathways of the whole electrode but also relieve the induced stress upon volume changes. Additionally, the robust frameworks constructed by homogeneous distribution of inactive Nd₂H₅ based on a molecular level could effectively alleviate the volume expansion and phase separation of thus-confined MgH₂ and Mg₂NiH₄. More importantly, it is theoretically and experimentally verified that the uniform distribution of Nd₂H₅, which is an electronic conductor with a Li-ion diffusion barrier that is much lower than that of MgH₂ and Mg₂NiH₄, could further facilitate the electron and Li-ion transfer of MgH₂ and Mg₂NiH₄. Consequently, the space-confined MgH₂ and Mg₂NiH₄ deliver a reversible capacity of 997 mAh g^-1 at 2038 mA g^-1 after 100 cycles.

Vaporization-Controlled Energy Release Mechanisms Underlying the Exceptional Reactivity of Magnesium Nanoparticles

Magnesium nanoparticles (NPs) offer the potential of high-performance reactive materials from both thermodynamic and kinetic perspectives. However, the fundamental energy release mechanisms and kinetics have not been explored due to the lack of facile synthetic routes to high-purity Mg NPs. Here, a vapor-phase route to surface-pure, core-shell nanoscale Mg particles is presented, whereby controlled evaporation and growth are utilized to tune particle sizes (40-500 nm), and their size-dependent reactivity and energetic characteristics are evaluated. Extensive in situ characterizations shed light on the fundamental reaction mechanisms governing the energy release of Mg NP-based energetic composites across particle sizes and oxidizer chemistries. Direct observations from in situ transmission electron microscopy and high-speed temperature-jump/time-of-flight mass spectrometry coupled with ignition characterization reveal that the remarkably high reactivity of Mg NPs is a direct consequence of enhanced vaporization and Mg release from their high-energy surfaces that result in the accelerated energy release kinetics from their composites. Mg NP composites also demonstrate mitigated agglomeration and sintering during reaction due to rapid gasification, enabling complete energy extraction from their oxidation. This work expands the compositional possibilities of nanoscale solid fuels by highlighting the critical relationships between metal volatilization and oxidative energy release from Mg NPs, thus opening new opportunities for strategic design of functional Mg-based nanoenergetic materials for tunable energy release.

Confining Nano-GeP in Nitrogenous Hollow Carbon Fibers toward Flexible and High-Performance Lithium-Ion Batteries

Although graphite has been used as anodes of lithium-ion batteries (LiBs) for 30 years, its unsatisfactory energy density makes it insufficient toward some new electronic products such as unmanned aerial vehicles. Herein, in situ synthesis of nano-GeP confined in nitrogen-doped carbon (GeP@NC) fibers was designed and performed via coaxial electrospinning followed by a phosphating process. This way ensured the paper-like GeP@NC-x electrode with high conductivity, high flexibility, and lightweight properties, which simultaneously solved the key scientific problems of difficulty in structural design and severe volume expansion of GeP. The inner diameter and wall thickness of the nanofibers can be effectively controlled by adjusting the size of electrospinning needles. It was suggested that the fibers not only effectively inhibited the growth of GeP, resulting in the synthesis of nano-GeP with size less than 50 nm, but also alleviated the volume expansion/agglomeration and improved the diffusion kinetics of Li⁺ in nano-GeP during cycling. The Li⁺ diffusion coefficient can be improved by reducing the inner diameter and wall thickness of the fibers. As a model system, the paper-like electrode (GeP@NC-2) with a fiber diameter of 280 nm and a wall thickness of 110 nm exhibited the best electrochemical performance. When applied as anodes in LiBs, it displayed a reversible capacity of 612 mAh g^-1 at the 600th cycle at 1 A g^-1, while GeP@NC-0 with a solid structure only delivered 239 mAh g^-1. Furthermore, the GeP@NC-2 also exhibited good long-term cycling stability at 5 A g^-1, and the capacity displayed a slight difference of 221.2 and 209.0 mAh g^-1 in a voltage range of 0∼3 V and 0∼1.5 V, respectively. The well-defined synthetic approach combined with unique nanostructural design provided a meaningful reference for the rational design and development of next-generation flexible and high-performance LiB anodes.

Nanoscale Assembly of 2D Materials for Energy and Environmental Applications

Rational design of 2D materials is crucial for the realization of their profound implications in energy and environmental fields. The past decade has witnessed significant developments in 2D material research, yet a number of critical challenges remain for real-world applications. Nanoscale assembly, precise control over the orientational and positional ordering, and complex interfaces among 2D layers are essential for the continued progress of 2D materials, especially for energy storage and conversion and environmental remediation. Herein, recent progress, the status, future prospects, and challenges associated with nanoscopic assembly of 2D materials are highlighted, specifically targeting energy and environmental applications. Geometric dimensional diversity of 2D material assembly is focused on, based on novel assembly mechanisms, including 1D fibers from the colloidal liquid crystalline phase, 2D films by interfacial tension (Marangoni effect), and 3D nanoarchitecture assembly by electrochemical processes. Relevant critical advantages of 2D material assembly are highlighted for application fields, including secondary batteries, supercapacitors, catalysts, gas sensors, desalination, and water decontamination.

A Review of the MSCA ITN ECOSTORE—Novel Complex Metal Hydrides for Efficient and Compact Storage of Renewable Energy as Hydrogen and Electricity

Hydrogen as an energy carrier is very versatile in energy storage applications. Developments in novel, sustainable technologies towards a CO2-free society are needed and the exploration of all-solid-state batteries (ASSBs) as well as solid-state hydrogen storage applications based on metal hydrides can provide solutions for such technologies. However, there are still many technical challenges for both hydrogen storage material and ASSBs related to designing low-cost materials with low-environmental impact. The current materials considered for all-solid-state batteries should have high conductivities for Na+, Mg2+ and Ca2+, while Al3+-based compounds are often marginalised due to the lack of suitable electrode and electrolyte materials. In hydrogen storage materials, the sluggish kinetic behaviour of solid-state hydride materials is one of the key constraints that limit their practical uses. Therefore, it is necessary to overcome the kinetic issues of hydride materials before discussing and considering them on the system level. This review summarizes the achievements of the Marie Skłodowska-Curie Actions (MSCA) innovative training network (ITN) ECOSTORE, the aim of which was the investigation of different aspects of (complex) metal hydride materials. Advances in battery and hydrogen storage materials for the efficient and compact storage of renewable energy production are discussed.

Power Generation by Selective Self-Assembly of Biocatalysts

Through a careful chemical and bioelectronic design we have created a system that uses self-assembly of enzyme-nanoparticle hybrids to yield bioelectrocatalytic functionality and to enable the harnessing of electrical power from biomass. Here we show that mixed populations of hybrids acting as catalyst carriers for clean energy production can be efficiently stored, self-assembled on functionalized stationary surfaces, and magnetically re-collected to make the binding sites on the surfaces available again. The methodology is based on selective interactions occurring between chemically modified surfaces and ligand-functionalized hybrids. The design of a system with minimal cross-talk between the particles, outstanding selective binding of the hybrids at the electrode surfaces, and direct anodic and cathodic electron transfer pathways leads to mediator-less bioelectrocatalytic transformations which are implemented in the construction of a fast self-assembling, membrane-less fructose/O₂ biofuel cell.

Hydrangea-Shaped 3D Hierarchical Porous Magnesium Hydride-Carbon Framework with High Rate Performance for Lithium Storage

Magnesium hydride (MgH₂) is a promising anode material for lithium-ion batteries (LIBs) by virtue of its high theoretical specific capacity, suitable potential, and abundant source. However, the electrochemical performance of the MgH₂ electrode is still far from satisfactory due to its poor electronic conductivity and fast capacity decay. In this paper, a hydrangea-shaped three-dimensional (3D) hierarchical magnesium hydride-carbon framework (MH@HyC) comprising MgH₂ nanoparticles (NPs) uniformly self-assembled on hierarchical porous carbon (HyC) is fabricated for advanced lithium storage. Featuring high surface area and a well-defined macro-meso-micropore structure, HyC plays an ideal structure-directing role for the growth of MgH₂ NPs with size control, high loading, and a hydrangea-shape array. Taking advantage of the robust 3D hierarchical porous structure and the derived interactions, MH@HyC not only provides sufficient electrochemically active sites and enhances the electronic conductivity and channels for rapid transfer of electrons/Li ions but also relieves the agglomeration and accommodates the volumetric effects during cycling, leading to high capacity utilization, fast electrochemical kinetics, and well-sustained structural integrity. As a result, MH@HyC delivers a high reversible capacity of 554 mAh g^-1 after 1000 cycles at a high current rate of 2 A g^-1, enabling it a potential anode candidate for LIBs.

Generalized On-Demand Production of Nanoparticle Monolayers on Arbitrary Solid Surfaces via Capillarity-Mediated Inverse Transfer

Century-old Langmuir monolayer deposition still represents the most convenient approach to the production of monolayers of colloidal nanoparticles on solid substrates for practical biological and chemical-sensing applications. However, this approach simply yields arbitrarily shaped large monolayers on a flat surface and is strongly limited by substrate topography and interfacial energy. Here, we describe a generalized and facile method of rapidly producing uniform monolayers of various colloidal nanoparticles on arbitrary solid substrates by using an ordinary capillary tube. Our method is based on an interesting finding of inversion phenomenon of a nanoparticle-laden air-water interface by flowing through a capillary tube in a manner that prevents the particles from adhesion to the capillary sidewall, thereby presenting the nanoparticles face-first at the tube's opposite end for direct and one-step deposition onto a substrate. We show that our method not only allows the placement of a nanoparticle monolayer at target locations of solid substrates regardless of their surface geometry and adhesion but also enables the production of monolayers containing nanoparticles with different size, shape, surface charge, and composition. To explore the potential of our approach, we demonstrate the facile integration of gold nanoparticle monolayers into microfluidic devices for the real-time monitoring of molecular Raman signals under dynamic flow conditions. Moreover, we successfully extend the use of our method to developing on-demand Raman sensors that can be built directly on the surface of consumer products for practical chemical sensing and fingerprinting. Specifically, we achieve both the pinpoint deposition of gold nanoparticle monolayers and sensitive molecular detection from the deposited region on clothing fabric for the detection of illegal drug substances, a single grain of rice and an orange for pesticide monitoring, and a $100 bill as a potential anti-counterfeit measure, respectively. We believe that our method will provide unique opportunities to expand the utility of colloidal nanoparticles and to greatly improve the accessibility of nanoparticle-based sensing technologies.

Sn nanocrystals embedded in porous TiO2/C with improved capacity for sodium-ion batteries

A cylinder-like Sn/TiO₂/C composite was prepared by carbonization and exhibited improved specific capacity in SIBs due to the combination of a porous TiO₂/C structure and Sn nanocrystals.

Nb2O5 Nanoparticles Anchored on an N-Doped Graphene Hybrid Anode for a Sodium-Ion Capacitor with High Energy Density

Sodium-ion capacitors (SICs) have gained great interest for mid- to large-scale energy storage applications because of their high energy and high power densities as well as long cycle life and low cost. Herein, a T-Nb₂O₅ nanoparticles/N-doped graphene hybrid anode (T-Nb₂O₅/NG) was prepared by solvothermal treating a mixed ethanol solution of graphene oxide (GO), urea, and NbCl₅ at 180 °C for 12 h, followed by calcining at 700 °C for 2 h, in which T-Nb₂O₅ nanoparticles with average size of 17 nm were uniformly anchored on the surface of the nitrogen-doped reduced GO because their growth and aggregation were hindered, and also, the electronic conductivity and the active sites of T-Nb₂O₅/NG were improved by doping nitrogen. The T-Nb₂O₅/NG anode showed superior rate capability (68 mA h g^-1 even at 2 A g^-1) and good cycling life (106 mA h g^-1 at 0.2 A g^-1 for 200 cycles and 83 mA h g^-1 at 1 A g^-1 for 1000 cycles) and also showed high-rate pseudocapacitive behavior from kinetics analysis. A novel SIC system had been constructed by using the T-Nb₂O₅/NG as anode and commercially activated carbon as the cathode; it delivered an energy density of 40.5 W h kg^-1 at a power density of 100 W kg^-1 and a long-term cycling stability (capacity retention of 63% after 5000 consecutive cycles at a current density of 1 A g^-1) and showed a promising application for highly efficient energy storage systems.

Construction of 3D architectures with Ni(HCO3)2 nanocubes wrapped by reduced graphene oxide for LIBs: ultrahigh capacity, ultrafast rate capability and ultralong cycle stability

A 3D layered Ni(HCO₃)₂/rGO nano-architecture was fabricated by coordination self-assembly for high performance storage of Li-ions with fast electrode kinetics and a super-long life.

Rechargeable lithium-ion batteries (LIBs) have been the dominating technology for electric vehicles (EV) and grid storage in the current era, but they are still extensively demanded to further improve energy density, power density, and cycle life. Herein, a novel 3D layered nanoarchitecture network of Ni(HCO₃)₂/rGO composites with highly uniform Ni(HCO₃)₂ nanocubes (average diameter of 100 ± 20 nm) wrapped in rGO films is facilely fabricated by a one-step hydrothermal self-assembly process based on the electrostatic interaction and coordination principle. Benefiting from the synergistic effects, the Ni(HCO₃)₂/rGO electrode delivers an ultrahigh capacity (2450 mA h g^–1 at 0.1 A g^–1), ultrafast rate capability and ultralong cycling stability (1535 mA h g^–1 for the 1000^th cycle at 5 A g^–1, 803 mA h g^–1 for the 2000^th cycle at 10 A g^–1). The detailed electrochemical reaction mechanism investigated by in situ XRD further indicates that the 3D architecture of Ni(HCO₃)₂/rGO not only provides a good conductivity network and has a confinement effect on the rGO films, but also benefits from the reversible transfer from LiHCO₃ to Li_xC₂ (x = 0–2), further oxidation of nickel, and the formation of a stable/durable solid electrolyte interface (SEI) film (LiF and LiOH), which are responsible for the excellent storage performance of the Li-ions. This work could shed light on the design of high-capacity and low-cost anode materials for high energy storage in LIBs to meet the critical demands of EV and mobile information technology devices.

Molecular-Scale Functionality on Graphene To Unlock the Energy Capabilities of Metal Hydrides for High-Capacity Lithium-Ion Batteries

Metal hydrides have attracted great intentions as anodes for lithium-ion batteries (LIBs) due to their extraordinary theoretical capacity. It is an unsolved challenge, however, to achieve high capacity with stable cyclability, owing to their insulating property and large volume expansion upon lithium storage. Here, we introduce self-initiated polymerization to realize molecular-scale functionality of metal hydrides with conductive polymer, that is, polythiophene (PTh), on graphene, leading to the formation of MgH₂@PTh core-shell nanoparticles on graphene. The nanoscale characteristics of MgH₂ not only relieve the induced stress upon volume changes but also allow fast diffusivity and high reactivity for Li-ion transport. More importantly, the conformal coating of ultrathin PTh membrane can effectively suppress the detrimental reactions between MgH₂ and electrolyte, provide enhanced performance with facile electron and Li⁺ transport, and preserve its structural integrity, attributed to the strong molecular interaction between PTh and MgH₂ as well as its various products during electrochemical reactions. With this structure, a high reversible specific capacity of 1311 mAh g^-1 at 100 mA g^-1, excellent rate performance of 1025 mAh g^-1 at 2000 mA g^-1, and a capacity retention of 84.5% at 2000 mA g^-1 after 500 cycles are observed for MgH₂@PTh nanoparticles as anode for LIBs.

High Areal Capacity Li-Ion Storage of Binder-Free Metal Vanadate/Carbon Hybrid Anode by Ion-Exchange Reaction

Storing more energy in a limited device area is very challenging but crucial for the applications of flexible and wearable electronics. Metal vanadates have been regarded as a fascinating group of materials in many areas, especially in lithium-ion storage. However, there has not been a versatile strategy to synthesize flexible metal vanadate hybrid nanostructures as binder-free anodes for Li-ion batteries so far. A convenient and versatile synthesis of M_x V_y O_x+2.5y @carbon cloth (M = Mn, Co, Ni, Cu) composites is proposed here based on a two-step hydrothermal route. As-synthesized products demonstrate hierarchical proliferous structure, ranging from nanoparticles (0D), and nanobelts (1D) to a 3D interconnected network. The metal vanadate/carbon hybrid nanostructures exhibit excellent lithium storage capability, with a high areal specific capacity up to 5.9 mAh cm^-2 (which equals to 1676.8 mAh g^-1 ) at a current density of 200 mA g^-1 . Moreover, the nature of good flexibility, mixed valence states, and ultrahigh mass loading density (over 3.5 mg cm^-2 ) all guarantee their great potential in compact energy storage for future wearable devices and other related applications.