Synergistic Engineering of CoO/MnO Heterostructures Integrated with Nitrogen-Doped Carbon Nanofibers for Lithium-Ion Batteries.

The integration of heterostructures within electrode materials is pivotal for enhancing electron and Li-ion diffusion kinetics. In this study, we synthesized CoO/MnO heterostructures to enhance the electrochemical performance of MnO using a straightforward electrostatic spinning technique followed by a meticulously controlled carbonization process, which results in embedding heterostructured CoO/MnO nanoparticles within porous nitrogen-doped carbon nanofibers (CoO/MnO/NC). As confirmed by density functional theory calculations and experimental results, CoO/MnO heterostructures play a significant role in promoting Li+ ion and charge transfer, improving electronic conductivity, and reducing the adsorption energy. The accelerated electron and Li-ion diffusion kinetics, coupled with the porous nitrogen-doped carbon nanofiber structure, contribute to the exceptional electrochemical performance of the CoO/MnO/NC electrode. Specifically, the as-prepared CoO/MnO/NC exhibits a high reversible specific capacity of 936 mA h g-1 at 0.1 A g-1 after 200 cycles and an excellent high-rate capacity of 560 mA h g-1 at 5 A g-1, positioning it as a competitive anode material for lithium-ion batteries. This study underscores the critical role of electronic and Li-ion regulation facilitated by heterostructures, offering a promising pathway for designing transition metal oxide-based anode materials with high performances for lithium-ion batteries.

The impact of support electronegativity on the electrochemical properties of platinum.

Modulating the electronic structure of platinum (Pt) through a support is an important strategy for enhancing its electrocatalytic properties. In this work, to explore the impact of support electronegativity on Pt's catalytic activity for hydrogen evolution, we chose diverse metals with varying electronegativities that are stable in acidic solutions, such as titanium (Ti), molybdenum (Mo), and tungsten (W), as supports. Ti is the optimal support according to density functional theory (DFT) calculations. As expected, the Pt@Ti catalyst demonstrated remarkable efficiency in the hydrogen evolution reaction (HER), displaying a minimal overpotential of 13 mV at -10 mA cm-2, a Tafel slope of 34.5 mV dec-1, and sustained durability over 110 h in a 0.5 M H2SO4 solution. To unravel the metal-support interaction (MSI) between Pt and Ti, a comprehensive exploration encompassing both experimental investigations and DFT calculations was undertaken. The results elucidate that the outstanding HER performance of Pt@Ti stems from robust synergies forged between Pt and Ti atoms within the Ti support. This work not only furnishes a technique for producing electrocatalysts with superior efficiency and stability but also streamlines the process of choosing the most appropriate metal support. Moreover, it enhances comprehension of the interaction between Pt and the metal support.

Constructing Abundant Oxygen-Containing Functional Groups in Hard Carbon Derived from Anthracite for High-Performance Sodium-Ion Batteries.

Hard carbon is regarded as one of the greatest potential anode materials for sodium-ion batteries (SIBs) because of its affordable price and large layer spacing. However, its poor initial coulombic efficiency (ICE) and low specific capacity severely restrict its practical commercialization in SIBs. In this work, we successfully constructed abundant oxygen-containing functional groups in hard carbon by using pre-oxidation anthracite as the precursor combined with controlling the carbonization temperature. The oxygen-containing functional groups in hard carbon can increase the reversible Na+ adsorption in the slope region, and the closed micropores can be conducive to Na+ storage in the low-voltage platform region. As a result, the optimal sample exhibits a high initial reversible sodium storage capacity of 304 mAh g-1 at 0.03 A g-1, with an ICE of 67.29% and high capacitance retention of 95.17% after 100 cycles. This synergistic strategy can provide ideas for the design of high-performance SIB anode materials with the intent to regulate the oxygen content in the precursor.

Machine Learning-Assisted Low-Dimensional Electrocatalysts Design for Hydrogen Evolution Reaction.

Efficient electrocatalysts are crucial for hydrogen generation from electrolyzing water. Nevertheless, the conventional "trial and error" method for producing advanced electrocatalysts is not only cost-ineffective but also time-consuming and labor-intensive. Fortunately, the advancement of machine learning brings new opportunities for electrocatalysts discovery and design. By analyzing experimental and theoretical data, machine learning can effectively predict their hydrogen evolution reaction (HER) performance. This review summarizes recent developments in machine learning for low-dimensional electrocatalysts, including zero-dimension nanoparticles and nanoclusters, one-dimensional nanotubes and nanowires, two-dimensional nanosheets, as well as other electrocatalysts. In particular, the effects of descriptors and algorithms on screening low-dimensional electrocatalysts and investigating their HER performance are highlighted. Finally, the future directions and perspectives for machine learning in electrocatalysis are discussed, emphasizing the potential for machine learning to accelerate electrocatalyst discovery, optimize their performance, and provide new insights into electrocatalytic mechanisms. Overall, this work offers an in-depth understanding of the current state of machine learning in electrocatalysis and its potential for future research.

Realizing Ultrafast and Robust Sodium-Ion Storage of Iron Sulfide Enabled by Heteroatomic Doping and Regulable Interface Engineering.

Fe-based sulfides are a promising type of anode material for sodium-ion batteries (SIBs) due to their high theoretical capacities and affordability. However, these materials often suffer from issues such as capacity deterioration and poor conductivity during practical application. To address these challenges, an N-doped Fe7S8 anode with an N, S co-doped porous carbon framework (PPF-800) was synthesized using a template-assisted method. When serving as an anode for SIBs, it delivers a robust and ultrafast sodium storage performance, with a discharge capacity of 489 mAh g-1 after 500 cycles at 5 A g-1 and 371 mAh g-1 after 1000 cycles at 30 A g-1 in the ether-based electrolyte. This impressive performance is attributed to the combined influence of heteroatomic doping and adjustable interface engineering. The N, S co-doped carbon framework embedded with Fe7S8 nanoparticles effectively addresses the issues of volumetric expansion, reduces the impact of sodium polysulfides, improves intrinsic conductivity, and stimulates the dominant pseudocapacitive contribution (90.3% at 2 mV s-1). Moreover, the formation of a stable solid electrolyte interface (SEI) film by the effect of uniform pore structure in ether-based electrolyte produces a lower transfer resistance during the charge-discharge process, thereby boosting the rate performance of the electrode material. This work expands a facile strategy to optimize the electrochemical performance of other metal sulfides.

Synergistic Structure and Iron-Vacancy Engineering Realizing High Initial Coulombic Efficiency and Kinetically Accelerated Lithium Storage in Lithium Iron Oxide.

Transition metal oxides with high capacity still confront the challenges of low initial coulombic efficiency (ICE, generally <70%) and inferior cyclic stability for practical lithium-storage. Herein, a hollow slender carambola-like Li0.43 FeO1.51 with Fe vacancies is proposed by a facile reaction of Fe3+ -containing metal-organic frameworks with Li2 CO3 . Synthesis experiments combined with synchrotron-radiation X-ray measurements identify that the hollow structure is caused by Li2 CO3 erosion, while the formation of Fe vacancies is resulted from insufficient lithiation process with reduced Li2 CO3 dosage. The optimized lithium iron oxides exhibit remarkably improved ICE (from 68.24% to 86.78%), high-rate performance (357 mAh g-1 at 5 A g-1 ), and superior cycling stability (884 mAh g-1 after 500 cycles at 0.5 A g-1 ). Paring with LiFePO4 cathodes, the full-cells achieve extraordinary cyclic stability with 99.3% retention after 100 cycles. The improved electrochemical performances can be attributed to the synergy of structural characteristics and Fe vacancy engineering. The unique hollow structure alleviates the volume expansion of Li0.43 FeO1.51 , while the in situ generated Fe vacancies are powerful for modulating electronic structure with boosted Li+ transport rate and catalyze more Li2 O decomposition to react with Fe in the first charge process, hence enhancing the ICE of lithium iron oxide anode materials.

Ni activated Mo2C by regulating the interfacial electronic structure for highly efficient lithium-ion storage.

Regulating the electronic structure plays a positive role in improving the ion/electron kinetics of electrode materials for lithium ion batteries (LIBs). Herein, an effective approach is demonstrated to achieve Ni/Mo2C hybrid nanoparticles embedded in porous nitrogen-doped carbon nanofibers (Ni/Mo2C/NC). Density functional theory calculations indicate that Ni can activate the interface of Ni/Mo2C by regulating the electronic structure, and accordingly improve the electron/Li-ion diffusion kinetics. The charge at the interface transfers from Ni atoms to Mo atoms on the surface of Mo2C, illustrating the formation of an interfacial electric field in Ni/Mo2C. The formed interfacial electric field in Ni/Mo2C can improve the intrinsic electronic conductivity, and reduce the Li adsorption energy and the Li+ diffusion barrier. Thus, the obtained Ni/Mo2C/NC shows an excellent high-rate capability of 344.1 mA h g-1 at 10 A g-1, and also displays a superior cyclic performance (remaining at 412.7 mA h g-1 after 1800 cycles at 2 A g-1). This work demonstrates the important role of electronic structure regulation by assembling hybrid materials and provides new guidance for future work on designing novel electrode materials for LIBs.

Strong electronic metal-support interaction between Pt and stainless mesh for enhancing the hydrogen evolution reaction.

Strong electronic metal-support interaction (EMSI) can tailor the electronic structure of electrocatalysts. Herein, Pt nanoparticles anchored on stainless mesh (SM) via EMSI engineering are reported, exhibiting excellent hydrogen production activity. Theoretical calculations demonstrate that the superior performance stems from the strong EMSI between Pt atoms and Fe atoms in SM.

Regulating the electronic structure of MoO2/Mo2C/C by heterostructure and oxygen vacancies for boosting lithium storage kinetics.

The electronic structure regulation of electrode materials can improve the ion/electron kinetics, which is beneficial to the cyclic performance and rate capability for lithium ion batteries (LIBs). Herein, we propose a facile strategy to achieve a MoO2/Mo2C/C heterostructure with abundant oxygen vacancies. Density functional theory calculations indicate that the heterostructure of MoO2/Mo2C/C can significantly promote the Li+/charge transfer and reduce the Li adsorption energy, and the abundant oxygen vacancies in MoO2/Mo2C/C can improve the intrinsic electronic conductivity and reduce the Li+ diffusion barrier. Benefiting from the multiscale coordinated regulation, the obtained MoO2/Mo2C/C film exhibits outstanding high rate capability (454.7 mA h g-1 at 5 A g-1) and remarkable cyclic performance (retaining 569 mA h g-1 over 1000 cycles at 2 A g-1). The insightful findings in this study can shed light on the behavior of the electron/ion structure regulation by the heterostructure and oxygen vacancies, which can guide future studies on designing other electrode materials with high-performance lithium-ion storage.

Optimizing electronic structure of porous Ni/MoO2 heterostructure to boost alkaline hydrogen evolution reaction.

Heterostructure engineering is an efficient strategy to synergisticallyimprove electrocatalytic activity. In this work, Ni/MoO2 heterojunction nanorods with porous structure self-supported on nickel foam (NF) are elaborately designed through a facile solution-evaporationmethod followed by a thermal reduction process. Prominently, the optimal electrocatalyst Ni/MoO2@NF-E delivers an exceptionally low overpotential of 19 mV at the current density of 10 mA cm-2 and a small Tafel slope of 52.3 mV dec-1 toward the hydrogen evolution reaction (HER) in alkaline solution. Concurrently, Ni/MoO2@NF-E also maintains excellent stability after 120 h of electrolysis or 5000 cyclic voltammetry cycles. The experimental and density functional theory (DFT) results indicate that the enhanced HER performance of Ni/MoO2@NF-E should be ascribed to the porous structure in the Ni/MoO2 nanorods providing more active catalytic site, the moderate Gibbs free energy of hydrogen adsorption (ΔGH*), as well as strong synergistic effect between Ni and MoO2. This work provides an efficient route for developing HER electrocatalysts in alkaline media.

Controlled Synthesis of Ultrafine ß-Mo2C Nanoparticles Encapsulated in N-Doped Porous Carbon for Boosting Lithium Storage Kinetics.

Rational construction of anode material architecture to afford excellent cycling stability, fast rate capacity, and large specific capacity is essential to promote further development of lithium-ion batteries in commercial applications. In this work, we propose a facile strategy to anchor ultrafine ß-Mo2C nanoparticles in N-doped porous carbon skeleton (ß-Mo2C@NC) using a scalable salt-template method. The well-defined and abundant hierarchical porous structure of ß-Mo2C@NC can not only significantly enhance the electron/ion transfer but also markedly increase the specific surface area to effectively expose the electrochemically accessible active sites. Besides, the N-doped carbon matrix can turn the d-orbital electrons of the Mo to boost the electron transportation as well as distribute active sites to buffer the volume change of Mo2C and provide conductive pathways during discharge/charge cycles. As a result, the as-prepared ß-Mo2C@NC displays excellent lithium storage performance in terms of 1701.6 mA h g-1 at 0.1 A g-1 after 100 cycles and a large capacity of 816.47 mA h g-1 at 2.0 A g-1 after 500 cycles. The above results distinctly demonstrate that the ß-Mo2C@NC composite has potential application as anode materials in high-performance energy storage devices.

Green and Scalable Fabrication of Sandwich-like NG/SiOx/NG Homogenous Hybrids for Superior Lithium-Ion Batteries.

SiOx is considered as a promising anode for next-generation Li-ions batteries (LIBs) due to its high theoretical capacity; however, mechanical damage originated from volumetric variation during cycles, low intrinsic conductivity, and the complicated or toxic fabrication approaches critically hampered its practical application. Herein, a green, inexpensive, and scalable strategy was employed to fabricate NG/SiOx/NG (N-doped reduced graphene oxide) homogenous hybrids via a freeze-drying combined thermal decomposition method. The stable sandwich structure provided open channels for ion diffusion and relieved the mechanical stress originated from volumetric variation. The homogenous hybrids guaranteed the uniform and agglomeration-free distribution of SiOx into conductive substrate, which efficiently improved the electric conductivity of the electrodes, favoring the fast electrochemical kinetics and further relieving the volumetric variation during lithiation/delithiation. N doping modulated the disproportionation reaction of SiOx into Si and created more defects for ion storage, resulting in a high specific capacity. Deservedly, the prepared electrode exhibited a high specific capacity of 545 mAh g-1 at 2 A g-1, a high areal capacity of 2.06 mAh cm-2 after 450 cycles at 1.5 mA cm-2 in half-cell and tolerable lithium storage performance in full-cell. The green, scalable synthesis strategy and prominent electrochemical performance made the NG/SiOx/NG electrode one of the most promising practicable anodes for LIBs.

Superhierarchical Conductive Framework Implanted with Nickel/Graphitic Carbon Nanocages as Sulfur/Lithium Metal Dual-Role Hosts for Li-S Batteries.

High-energy-density Li-S batteries (LSBs) are considered as a promising next-generation energy-storage system. However, the sluggish redox kinetics and severe polysulfide shuttle effect in elemental sulfur cathodes, along with uncontrollable dendrite propagation in lithium metal anodes, inevitably depress the electrochemical performance of LSBs and impede their practical implementation. Motivated by a unique hierarchical geometry, specific chemical affinity, and nitrogen-enriched collagen component of natural skin fibers (SFs), here we proposed an effective structural engineering strategy for crafting an SF-derived superhierarchical N-doped porous carbon framework in situ implanted with nickel/graphitic carbon nanocages as a dual-role host to simultaneously address the challenges faced on the sulfur cathode and lithium anode in LSBs. The experimental results and theoretical calculation disclose that the implanted Ni nanoparticles and highly graphitic sp2 carbon nanocages together with doped N heteroatoms not only provide a synergetic trapping-catalytic-conversion effect for regulating soluble polysulfides with promoted redox kinetics in the cathode at both room and elevated (55 °C) temperatures but also yield Ni-enhanced lithiophilic N-heteroatom active sites in the host framework to control Li deposition and suppress Li dendrite growth in anodes. Combining the cathodic and anodic improvements further achieves a superb rate and cycling performance in full LSB cells with stable Coulombic efficiency, showing great potential in developing reliable LSBs.

Hydrogel-derived VPO4/porous carbon framework for enhanced lithium and sodium storage.

Vanadium phosphate (VPO4) is attracting extensive attention because of its advantages of low cost, stable structure and high theoretical capacity. However, similar to other phosphates, VPO4 suffers from low electrical conductivity and large volume expansion, adversely influencing its electrochemical performance and thus limiting its application as an anode in lithium and sodium ion batteries. Herein, we propose a novel, facile strategy based on the organic-inorganic network of a nanostructured hybrid hydrogel for immobilizing VPO4 in a hierarchically porous carbon framework (3DHP-VPO4@C). VPO4 chemically interacts with the carbon framework via a P-C bond, functioning as a buffer layer to maintain structural stability during charge/discharge cycles. The carbon framework offers an efficient pathway for electron and Li+/Na+ transport to ensure high electronic conductivity of the electrode. The 3DHP-VPO4@C anode exhibits excellent lithium and sodium storage performances, and notably high capacities of 957 mA h g-1 at 0.1 A g-1 and 345.3 mA h g-1 at 5 A g-1 for lithium ion batteries. Full cells consisting of a LiFePO4 cathode and the 3DHP-VPO4@C anode also prove to have superior cycling stability and rate performance for LIBs.

V3S4 Nanosheets Anchored on N, S Co-Doped Graphene with Pseudocapacitive Effect for Fast and Durable Lithium Storage.

Construction of a suitable hybrid structure has been considered an important approach to address the defects of metal sulfide anode materials. V3S4 nanosheets anchored on an N, S co-coped graphene (VS/NSG) aerogel were successfully fabricated by an efficient self-assembled strategy. During the heat treatment process, decomposition, sulfuration and N, S co-doping occurred. This hybrid structure was not only endowed with an enhanced capability to buffer the volume expansion, but also improved electron conductivity as a result of the conductive network that had been constructed. The dominating pseudocapacitive contribution (57.78% at 1 mV s-1) enhanced the electrochemical performance effectively. When serving as anode material for lithium ion batteries, VS/NSG exhibits excellent lithium storage properties, including high rate capacity (480 and 330 mAh g-1 at 5 and 10 A g-1, respectively) and stable cyclic performance (692 mAh g-1 after 400 cycles at 2 A g-1).

Cr2O3 nanosheet/carbon cloth anode with strong interaction and fast charge transfer for pseudocapacitive energy storage in lithium-ion batteries.

Flexible lithium-ion batteries have attracted considerable interest for next-generation bendable, implantable and wearable electronics devices. Here, we have successfully grown Cr2O3 nanosheets on carbon cloth (CC) as freestanding anodes for Li-ion batteries (LIBs). Density functional theory (DFT) calculations verify an optimal structure of two-dimensional Cr2O3 nanosheets on the carbon fiber surface and a strong interaction between the O edges of Cr2O3 and the carbon. The interconnected Cr2O3 nanosheets with a large surface area enable fast charge transfer by efficient contact with electrolyte while the flexible CC substrate accommodates the volume change during cycles, leading to excellent rate capability and cyclic stability through psuedocapacitance-dominant energy storage. Full cells are assembled using the Cr2O3-CC anode and a LiFePO4 cathode, which deliver excellent capacity retention and rate capability. The fully-charged cell is demonstrated to power a red light-emitting diode (LED), verifying the potential of Cr2O3-CC as a promising anode material for LIBs.

Hollow SnO2 nanospheres with oxygen vacancies entrapped by a N-doped graphene network as robust anode materials for lithium-ion batteries.

The practical application of tin dioxide (SnO2) in lithium-ion batteries has been greatly hindered by its large volumetric expansion and low conductivity. Thus, a rational design of the size, geometry and the pore structure of SnO2-based nanomaterials is still a dire demand. To this end, herein we report an effective approach for engineering hollow-structured SnO2 nanospheres with adequate surface oxygen vacancies simultaneously wrapped by a nitrogen-doped graphene network (SnO2-x/N-rGO) through an electrostatic adsorption-induced self-assembly together with a thermal reduction process. The close electrostatic attraction achieved a tight and uniform combination of positively charged SnO2 nanospheres with negatively charged graphene oxide (GO), which can alleviate the aggregation and volume expansion of the entrapped SnO2 nanospheres. Subsequent thermal treatment not only ensures a significant reduction of the GO sheets accompanying nitrogen-doping, but also induces the generation of oxygen vacancies on the surface of the SnO2 hollow nanospheres, together building up a long-range and bicontinuous transfer channel for rapid electron and ion transport. Because of these structural merits, the as-built SnO2-x/N-rGO composite used as the anode material exhibits excellent robust cycling stability (∼912 mA h g-1 after 500 cycles at 0.5 A g-1 and 652 mA h g-1 after 200 cycles at 1 A g-1) and superior rate capability (309 mA h g-1 at 10 A g-1). This facile fabrication strategy may pave the way for the construction of high performance SnO2-based anode materials for potential application in advanced lithium-ion batteries.

Synthesis of Hierarchical Sisal-Like V2O5 with Exposed Stable {001} Facets as Long Life Cathode Materials for Advanced Lithium-Ion Batteries.

Vanadium pentoxide (V2O5) is considered a promising cathode material for advanced lithium-ion batteries owing to its high specific capacity and low cost. However, the application of V2O5-based electrodes has been hindered because of their inferior conductivity, cycling stability, and power performance. Herein, hierarchical sisal-like V2O5 microstructures consisting of primary one-dimensional (1D) nanobelts with [001] facets orientation growth and rich oxygen vacancies are synthesized through a facile hydrothermal process using polyoxyethylene-20-cetyl-ether as the surface control agent, followed by calcination. The primary 1D nanobelt shortens the transfer path of electrons and ions, and the stable {001} facets could reduce the side reaction at the interface of electrode/electrolyte, simultaneously. Moreover, the formation of low valence state vanadium would generate the oxygen vacancies to facilitate lithium-ion diffusion. As a result, the sisal-like V2O5 manifests excellent electrochemical performances, including high specific capacity (297 mA h g-1 at a current of 0.1 C) and robust cycling performance (capacity fading 0.06% per cycle). This work develops a controllable method to craft the hierarchical sisal-like V2O5 microstructures with excellent high rate and long-term cyclic stability.

Efficient Synthesis of Graphene Nanoscrolls for Fabricating Sulfur-Loaded Cathode and Flexible Hybrid Interlayer toward High-Performance Li-S Batteries.

A modified lyophilization approach is developed and used for highly efficient transformation of 2D graphene oxide sheet into 1D graphene nanoscroll (GNS) with high topological transforming efficiency (∼94%). Because of the unique open tubular structure and large specific surface area (545 m2 g-1), GNS is utilized for the first time as a porous cathode scaffold for encapsulating sulfur with a high loading (81 wt %), and also as a conductive skeleton for assembling MnO2 nanowires into a flexible free-standing hybrid interlayer, both enabling high-rate and long-life Li-S battery.

Template-Engaged Synthesis of 1D Hierarchical Chainlike LiCoO2 Cathode Materials with Enhanced High-Voltage Lithium Storage Capabilities.

A novel 1D hierarchical chainlike LiCoO2 organized by flake-shaped primary particles is synthesized via a facile template-engaged strategy by using CoC2O4·2H2O as a self-sacrificial template obtained from a simple coprecipitation method. The resultant LiCoO2 has a well-built hierarchical structure, consisting of secondary micrometer-sized chains and sub-micrometer-sized primary flakes, while these primary LiCoO2 flakes have specifically exposed fast-Li(+)-diffused active {010} facets. Owing to this unique hierarchical structure, the chainlike LiCoO2 serves as a stable cathode material for lithium-ion batteries (LIBs) operated at a high cutoff voltage up to 4.5 V, enabling highly reversible capacity, remarkable rate performance, and long-term cycle life. Specifically, the chainlike LiCoO2 can deliver a reversible discharge capacity as high as 168, 156, 150, and 120 mAh g(-1) under the current density of 0.1, 0.5, 1, and 5 C, respectively, while about 85% retention of the initial capacity can be retained after 200 cycles under 1 C at room temperature. Moreover, the chainlike LiCoO2 also shows an excellent cycling stability at a wide operating temperature range, showing the capacity retention of ∼73% after 200 cycles at 55 °C and of ∼68% after 50 cycles at -10 °C, respectively. The work described here suggests the great potential of the hierarchical chainlike LiCoO2 as high-voltage cathode materials aimed toward developing advanced LIBs with high energy density and power density.