Morphology-Conserved Transformations of Metal-Based Precursors to Hierarchically Porous Micro-/Nanostructures for Electrochemical Energy Conversion and Storage

Layered carbon nitride bulk as a versatile cathode material for fast ion batteries

The development of high-comprehensive-performance cathode materials is significant and urgent for ion battery systems. Based on density functional theory methods, we systematically expand and investigate a porous and van der Waals layered bulk structure of carbon nitride as a versatile cathode material for various ion batteries. The calculated results indicate that the layered bulk carbon nitride structure is a semiconductor material with good thermal stability. The structure has high-density one-dimensional transport channels for fast K/Na/Ca ion migration with low activation energy barriers of only 0.125, 0.281, and 0.296 eV, respectively. The theoretical specific capacity, open-circuit voltage, and energy density can reach 137, 150, and 273 mA h g-1, 3.788-3.614, 3.251-3.037, and 3.376-2.821 V, and 506.1, 470.8, and 847.3 W h kg-1 for K, Na and Ca ions, respectively. Compared to common cathode materials, layered carbon nitride possesses significant advantages such as fast ion migration, high energy density, low cost, and environmental friendliness.

Recent Development on Transition Metal Oxides-Based Core-Shell Structures for Boosted Energy Density Supercapacitors

In recent years, nanomaterials exploration and synthesis have played a crucial role in advancing energy storage research, particularly in supercapacitor development. Researchers have diversified materials, including metal oxides, chalcogenides, and composites, as well as carbon materials, to enhance energy and power density. Balancing energy density with electrochemical stability remains challenging, driving intensified efforts in advancing electrode materials. This review focuses on recent progress in designing and synthesizing core-shell materials tailored for supercapacitors. The core-shell architecture offers advantages such as increased surface area, redox active sites, electrical conductivity, ion diffusion kinetics, specific capacitance, and cyclability. The review explores the impact of core and shell materials, specifically transition metal oxides (TMOs), on supercapacitor electrochemical behavior. Metal oxide choices, such as cobalt oxide as a preferred core and manganese oxide as a shell, are discussed. The review also highlights characterization techniques for assessing structural, morphological, and electrochemical properties of core-shell materials. Overall, it provides a comprehensive overview of ongoing TMOs-based core-shell material research for supercapacitors, showcasing their potential to enhance energy storage for applications ranging from gadgets to electric vehicles. The review outlines existing challenges and future opportunities in evolving TMOs-based core-shell materials for supercapacitor advancements, holding promise for high-efficiency energy storage devices.

Modulation of Electronic Synergy to Enhance the Intrinsic Activity of Fe5Ni4S8 Nanosheets in Restricted Space Carbonized Wood Frameworks for Efficient Oxygen Evolution Reaction

Modulation of electronic structure and composition is widely recognized as an effective strategy to improve electrocatalyst performance. Herein, using a simple simultaneous carbonization and sulfidation strategy, NiFe double hydroxide-derived Fe5Ni4S8 (FNS) nanosheets immobilized on S-doped carbonized wood (SCW) framework by taking benefit of the orientation-constrained cavity and hierarchical porous structure of wood is proposed. Benefiting from the synergistic relationships between bimetal ions, the spatial confinement offered by the wood cavity, and the enhanced structural effects of the nanosheets array, the FNS/SCW exhibit enhanced intrinsic activity, increased accessibility of catalytically active sites, and convection-facilitated mass transport, resulting in an excellent oxygen evolution reaction (OER) activity and durability. Specifically, it takes a low overpotential of 230 mV at 50 mA cm-2 and potential increase is negligible (3.8%) at 50 mA cm-2 for 80 hours. Density functional theory (DFT) calculations further reveal that the synergistic effect of bimetal can optimize the electronic structure and lower the reaction energy barrier. The FNS/SCW used as the cathode of zinc-air battery shows higher power density and excellent durability relative to commercial RuO2, exhibiting a good application prospect. Overall, this research offers proposals for designing and producing effective OER electrocatalysts using sustainable resources.

Carbon-incorporated Ni2P-Fe2P hollow nanorods as superior electrocatalysts for the oxygen evolution reaction

A rational design and cost-effective transition metal-based hollow nanostructures are important for sustainable energy materials with high efficiency. This study reports on carbon-incorporated Ni₂P-Fe₂P hollow nanorods ((Ni,Fe)₂P/C HNRs) derived from a self-template approach as efficient electrocatalysts. Initially, a Ni₂(BDC)₂(DABCO)-MOF (Ni-MOF) is converted to NiFe-PBA hollow nanorods (HNRs) through facile ion exchange which was further converted to (Ni,Fe)₂P/C HNRs via a subsequent phosphidation process. The resulting (Ni,Fe)₂P/C HNRs exhibit remarkable activity for the oxygen evolution reaction in an alkaline solution requiring a small overpotential of 258 mV to drive a current density of 10 mA cm^-2 and long-term stability with little deactivation after 40 h. (Ni,Fe)₂P/C HNRs outperform (Ni,Fe)₂P/C NPs and commercial RuO₂. The unique hollow morphology and interfacial electronic structure substantially increase the active site and charge transfer rate of our electrocatalyst, resulting in excellent OER activity and stability.

Interface engineering of hierarchical NiCoP/NiCoSx heterostructure arrays for efficient alkaline hydrogen evolution at large current density

The development of non-noble metal electrocatalysts with high activity and long-term stability for the hydrogen evolution reaction (HER), especially at large current density, is of great significance for industrial hydrogen production from water using renewable electricity. Constructing heterostructures with interfacial interactions is an effective strategy to improve the catalytic performance for large-current-density HER. Herein, we innovatively present a facile two-step electrodeposition method to immobilize a hierarchical NiCoP/NiCoS_x heterostructure on Ni foam (NF) for alkaline HER. The strong interfacial coupling effect between NiCoP and NiCoS_x not only offers abundant active sites for fast electrochemical reaction, but also enhances the charge transfer ability accompanied by high electrical conductivity. Consequently, the obtained self-supporting NiCoP/NiCoS_x/NF exhibits an excellent catalytic performance with low overpotentials of 68, 144 and 222 mV to deliver current densities of 10, 100 and 500 mA cm^-2 in 1 M KOH, along with good stability for more than 110 h, outperforming most of the reported non-noble metal based HER catalysts. Density functional theory (DFT) results further confirm that this bimetal phosphide/sulfide heterostructure can synergistically optimize the Gibbs free energy of H* during the HER process, thus accelerating the HER reaction kinetics. This work provides a new strategy toward the rational design of large-current-density electrocatalysts, which have great potential in practical large-scale hydrogen production.

Bio-Inspired Hierarchical Micro-/Nanostructures for Anti-Icing Solely Fabricated by Metal-Assisted Chemical Etching

We report a cost-effective and scalable methodology for producing a hierarchical micro-/nanostructured silicon surface solely by metal-assisted chemical etching. It involves two major processing steps of fabricating micropillars and nanowires separately. The process of producing micro-scale structures by masked metal-assisted chemical etching was optimized. Silicon nanowires were created on the micropillar’s surface via maskless metal-assisted chemical etching. The hierarchical micro-/nanostructured surface exhibits superhydrophobic properties with a high contact angle of ~156° and a low sliding angle of <2.5° for deionized water. Furthermore, due to the existence of microscale and nanoscale air trapped at the liquid/solid interface, it exhibits a long ice delay time of 2876 s at −5 °C, more than 5 times longer than that of smooth surfaces. Compared to conventional dry etching methods, the metal-assisted chemical etching approach excludes vacuum environments and high-temperature processes and can be applied for applications requiring hierarchical micro-/nanostructured surfaces or structures.

Machine learning as a tool to engineer microstructures: Morphological prediction of tannin-based colloids using Bayesian surrogate models

ABSTRACT

Oxidized tannic acid (OTA) is a useful biomolecule with a strong tendency to form complexes with metals and proteins. In this study we open the possibility to further the application of OTA when assembled as supramolecular systems, which typically exhibit functions that correlate with shape and associated morphological features. We used machine learning (ML) to selectively engineer OTA into particles encompassing one-dimensional to three-dimensional constructs. We employed Bayesian regression to correlate colloidal suspension conditions (pH and pK _a) with the size and shape of the assembled colloidal particles. Fewer than 20 experiments were found to be sufficient to build surrogate model landscapes of OTA morphology in the experimental design space, which were chemically interpretable and endowed predictive power on data. We produced multiple property landscapes from the experimental data, helping us to infer solutions that would satisfy, simultaneously, multiple design objectives. The balance between data efficiency and the depth of information delivered by ML approaches testify to their potential to engineer particles, opening new prospects in the emerging field of particle morphogenesis, impacting bioactivity, adhesion, interfacial stabilization, and other functions inherent to OTA.

IMPACT STATEMENT

Tannic acid is a versatile bio-derived material employed in coatings, surface modifiers, and emulsion and growth stabilizers, which also imparts mild anti-viral health benefits. Our recent work on the crystallization of oxidized tannic acid (OTA) colloids opens the route toward further valuable applications, but here the functional properties tend to depend strongly on particle morphology. In this study, we eschew trial-and-error morphology exploration of OTA particles in favor of a data-driven approach. We digitalized the experimental observations and input them into a Gaussian process regression algorithm to generate morphology surrogate models. These help us to visualize particle morphology in the design space of material processing conditions, and thus determine how to selectively engineer one-dimensional or three-dimensional particles with targeted functionalities. We extend this approach to visualize other experimental outcomes, including particle yield and particle surface-to-volume ratio, which are useful for the design of products based on OTA particles. Our findings demonstrate the use of data-efficient surrogate models for general materials engineering purposes and facilitate the development of next-generation OTA-based applications.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1557/s43577-021-00183-4.

Organophosphorus Hybrid Solid Electrolyte Interphase Layer Based on LixPO4 Enables Uniform Lithium Deposition for High‐Performance Lithium Metal Batteries

Lithium metal is a promising anode candidate for the next‐generation rechargeable battery system because of its highest specific capacity and lowest potential. However, low Coulombic efficiency (CE) and the formation of Li dendrites during the cycling process seriously hinder its practical application. Here, an organophosphorus hybrid flexible solid electrolyte interphase (SEI) layer is proposed based on a surface chelation strategy using phytic acid (PA) as Li metal surface treatment chemicals. Different from the traditional SEI layer, the polynuclear complex between PA and Li+ serves as a “connecter” in this SEI layer, which not only ensures its mechanical flexibility but also improves its lithiophilic property and ionic conductivity. With these advantages, the Li || Cu cells exhibit a high CE of 99.0% over 500 cycles at a current density of 0.5 mA cm−2. Li || Li symmetrical cells can also maintain a stable Li plating/stripping process over 2500 h at a high current density of 10.0 mA cm−2. Besides, all Li metal batteries (Li || S, Li || NCM, Li || LFP et al.) based on this strategy exhibit long cycling life and high capacity retention. This surface chelation strategy is believed to offer a new avenue to fabricate a stable and efficient SEI layer for practical application of Li metal batteries.

In situ observation of the electrochemical lithiation of a single MnO@C nanorod electrode with core/shell structure

Transition metal oxides (TMOs) play a crucial role in lithium-ion batteries (LIBs) due to their high theoretical capacity, natural abundance, and benign environmental impact, but they suffer from limitations such as cyclability and high-rate discharge ability. One leading cause is the lithiation-induced volume expansion (LIVE) for "conversion"-type TMOs, which can result in high stress, fracture and pulverization. Using carbon layers is an effective strategy to provide effective volumetric accommodation for lithium-ion (Li⁺) insertion; however, the detailed mechanism is unknown. In order to clarify the working mechanism of nanoscale LIBs, herein, the discharge reactions in a nanoscale LIB were investigated through in situ environmental transmission electron microscopy (ETEM). Visualization of the Li⁺ insertion process of MnO@C nanorods (NRs) with core/shell structure (CSS) and internal void space (IVS) was achieved. The LIVE occurred in a consecutive two-step mode, i.e., a LIVE of the carbon layer followed by a co-LIVE of the carbon layer and MnO. No volume contraction of the IVS was observed. The IVS acted as a buffer relieving the stress of the carbon layer. The carbon layer with IVS simultaneously improved the cyclability and the high-rate discharge ability of the electrode, pointing to a promising route for building better TMO electrode materials.

Hollow Hydrangea-Like CoRu/Co Architecture as an Excellent Electrocatalyst for Oxygen Evolution

Developing low-cost but efficient electrocatalysts to promote the sluggish kinetics of oxygen evolution from water splitting is essential for hydrogen production. In this study, a hierarchical hollow hydrangea-like CoRu/Co superstructure is constructed through a self-templating method by morphology-controlled pyrolysis of flower-like Ru-doped Co-based layered double hydroxides (LDH). The anchoring of Ru into Co-LDH is the key to the formation of well-defined hydrangea-like three-dimensional superstructure composed of CoRu/Co. The optimized CoRu/Co-M-350 with a low Ru loading of 3.0 wt% exhibits excellent catalytic performances in the oxygen evolution reaction (OER) with low overpotential (η₁₀ =192 mV) and excellent stability for 100 h at 100 mA cm^-2 in alkaline media, outperforming the benchmark RuO₂ and most reported electrocatalysts. The superior morphology and structural features of CoRu/Co-M-350 provide not only abundant accessible surface sites but also fast mass and electron transfer, thereby promoting OER catalysis. The present study provides a new synthetic route for preparing highly active OER electrocatalysts.

Iron Selenide Microcapsules as Universal Conversion-Typed Anodes for Alkali Metal-Ion Batteries

Rechargeable alkali metal-ion batteries (AMIBs) are receiving significant attention owing to their high energy density and low weight. The performance of AMIBs is highly dependent on the electrode materials. It is, therefore, quite crucial to explore suitable electrode materials that can fulfil the future requirements of AMIBs. Herein, a hierarchical hybrid yolk-shell structure of carbon-coated iron selenide microcapsules (FeSe₂ @C-3 MCs) is prepared via facile hydrothermal reaction, carbon-coating, HCl solution etching, and then selenization treatment. When used as the conversion-typed anode materials (CTAMs) for AMIBs, the yolk-shell FeSe₂ @C-3 MCs show advantages. First, the interconnected external carbon shell improves the mechanical strength of electrodes and accelerates ionic migration and electron transmission. Second, the internal electroactive FeSe₂ nanoparticles effectively decrease the extent of volume expansion and avoid pulverization when compared with micro-sized solid FeSe₂ . Third, the yolk-shell structure provides sufficient inner void to ensure electrolyte infiltration and mobilize the surface and near-surface reactions of electroactive FeSe₂ with alkali metal ions. Consequently, the designed yolk-shell FeSe₂ @C-3 MCs demonstrate enhanced electrochemical performance in lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries with high specific capacities, long cyclic stability, and outstanding rate capability, presenting potential application as universal anodes for AMIBs.

Overview of transition metal-based composite materials for supercapacitor electrodes

Supercapacitors (SCs) can bridge the gap between batteries and conventional capacitors, playing a critical role as an efficient electrochemical storage device in intermittent renewable energy sources. Transition metal-based electrode materials have been investigated extensively as a class of electrode materials for SC application, but they have some limitations due to the sluggish ion/electron diffusion and inferior electronic conductivity, restricting their electrochemical performances towards energy storage. Developing advanced transition metal-based electrode materials is crucial for high energy density along with high specific power and fast charging/discharging rates towards high performance SCs. In this review, we highlight the state-of-the-art of transition metal-based electrode materials (transition metal oxides and their composites, transition metal sulfides and their composites, and transition metal phosphides and their composites), focusing on specific morphologies, components, and power characteristics. We also provide future prospects for transition metal-based electrode materials for SCs and hope this review will shed light on the achievement of higher performance and hold great promise in vast applications for future energy storage and conversion.

Enhanced catalytic activity of MIL-101(Fe) with coordinatively unsaturated sites for activating persulfate to degrade organic pollutants

In this work, four novel defective MIL-101(Fe) catalysts with coordinatively unsaturated sites were successfully prepared via a facile synthesis strategy by employing benzoic acid, acetic acid, oxalic acid, or citric acid as a modulator. The modified catalysts were demonstrated the existence of defects in the parent framework by a series of characterizations. As compared to the initial MIL-101(Fe), the electronic structure of defective MIL-101(Fe) catalyst was effectively adjusted; meanwhile, the coordinatively unsaturated Fe sites were efficiently generated and the pore sizes were enlarged. Besides, the defective MIL-101(Fe) catalysts exhibited excellent catalytic performance for rhodamine B degradation by persulfate activation. To be specific, the degradation rates of rhodamine B increased from 58.70 to 94.05%, 86.11%, 78.70%, and 82.62%, respectively. The defective MIL-101(Fe) with coordinatively unsaturated sites showed good reusability and stability, and the probable catalytic mechanism was also investigated.

Tailoring Low-Temperature Performance of a Lithium-Ion Battery via Rational Designing Interphase on an Anode

Performances of lithium-ion batteries at subambient temperatures are extremely restricted by the resistive interphases originated from electrolyte decomposition, especially on the anode surface. This work reports a novel strategy that an anode interphase of low impedance is constructed by applying an electrolyte additive dimethyl sulfite (DMS). Electrochemical measurements indicate that the as-constructed interphase provides graphite/LiNi_0.5Co_0.2Mn_0.3O₂ pouch cells with excellent low-temperature performance, outperforming the interphase constructed by 1,3,2-dioxathiolane 2,2-dioxide (DTD), a common commercially used electrolyte additive. Spectral characterizations in combination with theoretical calculations demonstrate that the improved performance is attributed to the unique molecular structure of DMS, which presents appropriate reduction activity and constructs the more stable and ionically conductive anode interphase due to the weaker combination of its reduction product with lithium ions than DTD. This rational design of interphases via an additive structure has been proven to be a low cost but rather an effective approach to tailor the performances of lithium-ion batteries.

Suspended-Template Electric-Assisted Nanoimprinting for Hierarchical Micro-Nanostructures on a Fragile Substrate

Coating hierarchical micro-nanostructures on the surface of optoelectronic devices has been demonstrated to improve the overall performance. However, fabricating desired structures on a fragile optoelectronic device substrate is still challenging. A suspended-template electric-assisted nanoimprinting technique is proposed herein to controllably fabricate hierarchical micro-nanostructures on a fragile substrate. The suspension design of the template ensures that it conveniently deforms to fully fit the surface fluctuation of the substrate. The deformation of template and the filling of liquid polymer in the micro/nanocavities of the template are both driven by the powerful surface/interface force generated by an electric field applied between the template and substrate surface, thus protecting the fragile substrate from squeezing damage. Different morphologies of hierarchical micro-nanostructures are fabricated by changing the electric field. Based on suspended-template electric-assisted nanoimprinting, the environmentally adaptable fully covering hierarchical micro-nanostructures are encapsulated on the surface of flip-film light-emitting diode chips, thus significantly enhancing their light management in complex environments.

Micro-Blooming: Hierarchically Porous Nitrogen-Doped Carbon Flowers Derived from Metal-Organic Mesocrystals

Synthesis of 3D flower-like zinc-nitrilotriacetic acid (ZnNTA) mesocrystals and their conformal transformation to hierarchically porous N-doped carbon superstructures is reported. During the solvothermal reaction, 2D nanosheet primary building blocks undergo oriented attachment and mesoscale assembly forming stacked layers. The secondary nucleation and growth preferentially occurs at the edges and defects of the layers, leading to formation of 3D flower-like mesocrystals comprised of interconnected 2D micropetals. By simply varying the pyrolysis temperature (550-1000 °C) and the removal method of in the situ-generated Zn species, nonporous parent mesocrystals are transformed to hierarchically porous carbon flowers with controllable surface area (970-1605 m² g^-1 ), nitrogen content (3.4-14.1 at%), pore volume (0.95-2.19 cm³ g^-1 ), as well as pore diameter and structures. The carbon flowers prepared at 550 °C show high CO₂ /N₂ selectivity due to the high nitrogen content and the large fraction of (ultra)micropores, which can greatly increase the CO₂ affinity. The results show that the physicochemical properties of carbons are highly dependent on the thermal transformation and associated pore formation process, rather than directly inherited from parent precursors. The present strategy demonstrates metal-organic mesocrystals as a facile and versatile means toward 3D hierarchical carbon superstructures that are attractive for a number of potential applications.

Chemically Binding Scaffolded Anodes with 3D Graphene Architectures Realizing Fast and Stable Lithium Storage

Three-dimensional (3D) graphene has emerged as an ideal platform to hybridize with electrochemically active materials for improved performances. However, for lithium storage, current anodic guests often exist in the form of nanoparticles, physically attached to graphene hosts, and therefore tend to detach from graphene matrices and aggregate into large congeries, causing considerable capacity fading upon repeated cycling. Herein, we develop a facile double-network hydrogel-enabled methodology for chemically binding anodic scaffolds with 3D graphene architectures. Taking tin-based alloy anodes as an example, the double-network hydrogel, containing interpenetrated cyano-bridged coordination polymer hydrogel and graphene oxide hydrogel, is directly converted to a physical-intertwined and chemical-bonded Sn-Ni alloy scaffold and graphene architecture (Sn-Ni/G) dual framework. The unique dual framework structure, with remarkable structural stability and charge-transport capability, enables the Sn-Ni/G anode to exhibit long-term cyclic life (701 mA h g-1 after 200 cycles at 0.1 A g-1) and high rate performance (497 and 390 mA h g-1 at 1 and 2 A g-1, respectively). This work provides a new perspective towards chemically binding scaffolded low-cost electrode and electrocatalyst materials with 3D graphene architectures for boosting energy storage and conversion.

Low-temperature pseudomorphic transformation of polyhedral MIL-88A to lithium ferrite (LiFe3O5) in aqueous LiOH medium toward high Li storage

The ability to develop novel nanomaterials, and to precisely manufacture their functional structures at the nano- and microscales would benefit many emerging device applications. Herein, as a first example, we describe the exploration of feasibility for the morphological replacement of an iron-based MOF bearing trimeric FeIII-O clusters, MIL-88A preform, with a polyhedral architecture of around 0.4 × 1.2 μm by a lithium ferrite (LiFe3O5) phase via solid-liquid pseudomorphic transformation reactions in biologically and environmentally favourable aqueous lithium hydroxide (LiOH). The reaction proceeds at 170 °C, and the overall reaction can be described as Fe3O(H2O)2(FMA)3(OH)·nH2O (MIL-88A) + 7OH- + Li+ → LiFe3O5 + 3FMA2- + (n + 6) H2O (FMA = fumarate). It was proposed that through the coordination substitution of a MOF ligand by OH-, follow-up dehydration and dehydroxylation, and final H+/Li+ ionic exchange, the monolithiated iron oxides formed thermodynamically at comparatively low temperatures, which transcribe the global nanostructure morphologies of the polyhedral MOF preforms with the hexagonal symmetry, but were composed of interconnected LiFe3O5 particles (about 16 nm) that crystallize in a typical magnetite-type cubic (Fd3[combining macron]m) structure. Given the characteristic texture and structure of the Li-Fe oxide replica, cubic LiFe3O5 was preferentially employed as a new type of electrode material in rechargeable lithium cells. Notably, from the electrochemical evaluation, this metal oxide system exhibits decent anodic performances by undergoing a nine-electron conversion reaction, showing a substantially high specific capacity with an average potential of 0.8 V versus lithium metal, a long service life (700 cycles), and exceptional high-rate capability (up to 2.0 A g-1). The synthetic paradigms demonstrated that the MIL-88A to LiFe3O5 conversion may be transferable to other advanced inorganic-based electrodes from the parent metal compound such as LiFeO2, LiMn2O4 or LiCoO2 toward sustainable energy fields.

Hierarchical Co3O4 Nano-Micro Arrays Featuring Superior Activity as Cathode in a Flexible and Rechargeable Zinc-Air Battery

All-solid-state zinc-air batteries are characterized as low cost and have high energy density, providing wearable devices with an ideal power source. However, the sluggish oxygen reduction and evolution reactions in air cathodes are obstacles to its flexible and rechargeable application. Herein, a strategy called MOF-on-MOF (MOF, metal-organic framework) is presented for the structural design of air cathodes, which creatively develops an efficient oxygen catalyst comprising hierarchical Co3O4 nanoparticles anchored in nitrogen-doped carbon nano-micro arrays on flexible carbon cloth (Co3O4@N-CNMAs/CC). This hierarchical and free-standing structure design guarantees high catalyst loading on air cathodes with multiple electrocatalytic activity sites, undoubtedly boosting reaction kinetics, and energy density of an all-solid-state zinc-air battery. The integrated Co3O4@N-CNMAs/CC cathode in an all-solid-state zinc-air battery exhibits a high open circuit potential of 1.461 V, a high capacity of 815 mAh g-1 Zn at 1 mA cm-2, a high energy density of 1010 Wh kg-1 Zn, excellent cycling stability as well as outstanding mechanical flexibility, significantly outperforming the Pt/C-based cathode. This work opens a new door for the practical applications of rechargeable zinc-air batteries in wearable electronic devices.

Tailoring Three-Dimensional Composite Architecture for Advanced Zinc-Ion Batteries

Rechargeable aqueous Zn-ion batteries (ZIBs) are of considerable interest for future energy storage. Their main limitation, however, is developing suitable cathode materials capable of sustaining the Zn²⁺ repeated intercalation/deintercalation. Herein, a three-dimensional polypyrrole (PPy)-encapsulated Mn₂O₃ composite architecture is developed for advanced ZIBs. The engineering can be easily realized via in situ phase transformation of MnCO₃ microboxes with subsequent self-initiated polymerization of PPy. The abundant open-up pores (∼30 nm) throughout the construction accelerate ion migration and provide a more active interface for Zn²⁺ storage in the Mn₂O₃@PPy bulk electrode. Meanwhile, the PPy skin uniformly wrapped on the Mn₂O₃ microbox not only guarantees a good conductive network for faster electron transport but also inhibits the dissolution of Mn₂O₃ and protects the integrity of the electrode from structural damage. As a result, the Mn₂O₃@PPy electrode can operate at reversible capacity exceeding those of most other cathode materials, but can still provide longer lifetime (no capacity decay over 2000 cycles at 0.4 A g^-1) and higher rate performance than others. Furthermore, theoretical studies show the H⁺ and Zn²⁺ coinsertion storage mechanism and reaction dynamics. The results show that this three-dimensional Mn₂O₃@PPy architecture is a promising cathode material for high-performance ZIBs.

Promotion of Overall Water Splitting Activity Over a Wide pH Range by Interfacial Electrical Effects of Metallic NiCo-nitrides Nanoparticle/NiCo2O4 Nanoflake/graphite Fibers

Many efforts have been made to develop bifunctional electrocatalysts to facilitate overall water splitting. Here, a fibrous bifunctional 3D electrocatalyst is reported for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) with high performance. The remarkable electrochemical performance is attributed of the catalysts to a number of factors: the metallic character of the three components (i.e., Ni3N, CoN, and NiCo2O4); the electronic structure, nanoflake-nanosphere network with abundant electroactive sites, and the electric field effect at the interfaces between different components. The oxide-nitride/graphite fibers have the lowest overpotential requirements of 71 and 183 mV at 10 mA cm-2 for HER and OER in alkaline medium, respectively. These values are comparable to those of commercial Pt/C (20 wt%) and RuO2. The electrodes also show a response to HER and OER in both neutral and acid media. Furthermore, the 3D structure can be highlighted by all-round electrodes for overall water splitting. The calculations on the changes in electrons transfer and the Femi level from oxides to oxides/nitrides reveal that the observed superb electrocatalytic performance can be attributed to the presence of Ni3N and CoN derived from the in situ nitridation of NiCo2O4.

Electrochemical Fabrication of Porous Au Film on Ni Foam for Nitrogen Reduction to Ammonia

Electrochemical reduction of N₂ to NH₃ provides an alternative strategy to replace the industrial Haber-Bosch process for facile and sustainable production of NH₃ . The development of efficient electrocatalysts for the nitrogen reduction reaction (NRR) is highly desired. Herein, a micelle-assisted electrodeposition method is presented for the direct fabrication of porous Au film on Ni foam (pAu/NF). Benefiting from its interconnected porous architectonics, the pAu/NF exhibits superior NRR performance with a high NH₃ yield rate of 9.42 µg h^-1 cm^-2 and a superior Faradaic efficiency of 13.36% at -0.2 V versus reversible hydrogen electrode under the neutral electrolyte (0.1 m Na₂ SO₄ ). The proposed micelle-assisted electrodeposition strategy is highly valuable for future design of active NRR catalysts with desired compositions toward various electrocatalysis fields.

Ethylene glycol-assisted fabrication and superb adsorption capacity of hierarchical porous flower-like magnesium oxide microspheres for phosphate

Hierarchical porous flower-like MgO microspheres were fabricated via an ethylene glycol-assisted route under mild conditions and exhibited an outstanding maximum adsorption capacity of 574.71 mg g⁻¹ for phosphate.

Relationships Between Crystal, Internal Microstructures, and Physicochemical Properties of Copper-Zinc-Iron Multinary Spinel Hierarchical Nano-microspheres

Rational design and fabrication of high quality complex multicomponent spinel ferrite with specific microstructures and solar light harvestings toward CO₂ reduction and antibiotic degradation to future energetic and catalytic applications are highly desirable. In this study, novel copper-zinc-iron multinary spinel hierarchical nano-microspheres (MSHMs) with different internal structures (solid nano-microspheres, yolk-shell hollow nano-microspheres, and double-shelled hollow nano-microspheres) have been successfully developed by a facile self-templated solvothermal strategy. The morphology and structure, optical, as well as photoinduced redox reactions including interfacial charge carrier behaviors and the intrinsic relationship of structure-property between intrinsic nano-microstructures and physicochemical performance of copper-zinc-iron ferrite MSHMs composites were systematically investigated with the assistance of various on- and/or off- line physical-chemical means and deeply elucidated in terms of the research outcomes. It is demonstrated that the modification of the interior microstructures can be applied to tune the catalytic properties of multinary spinel by tailoring the temperature programming to fine control the two opposite forces of contraction (Fc) and adhesion (Fa). Among various internal microstructures, the obtained double-shelled copper-zinc-iron MSHMs exhibited the superior catalytic performance toward 8.8 and 38 μmol for H₂ and CO productions as well as 80.4% removal of sulfamethoxazole antibiotics. As evidenced from primary characterizations, for example, combined steady-state PL, ns-TAS, and Mössbauer and sequential investigations, the remarkable improvements in the catalytic activity can be primarily attributed to several crucial factors, for example, the more effective e^--h⁺ spatial separations and interfacial transfers, multiple internal light scattering, higher photonic energy harvesting and effective reactive oxygen species generation with long radical lifetimes. The current research provides new insights into the molecular design of novel copper-zinc-iron multinary spinels and the intrinsic relationship of structure-property between interior structures (e.g., different crystal texture, morphologies structures) and the physicochemical performance of the aforementioned multinary spinels.

Hexamethylcucurbit[3,3]uril-Based Porous Supramolecular Assemblies and Their Adsorption Properties

In the present work, we selected hexamethylcucurbit[3,3]uril (Me6Q[3,3]) as a building block and obtained two Me6Q[3,3]-based porous supramolecular assemblies from neutral water (A) and aqueous HCl solutions (B), respectively. Both Me6Q[3,3]-based assemblies are constructed of Me6Q[3,3] molecules through the typical outer surface interaction of cucurbit[n]urils, as well as hydrogen bonding between latticed water molecules and portal carbonyl oxygens of Me6Q[3,3]. The assemblies present different porous structure features and exhibit different adsorption properties for eight common volatile organic compounds. However, the two porous assemblies exhibit similar adsorption properties for certain fluorophore dyes, including rhodamine B (G1), fluorescein (G2), and pyrene (G3), and form solid colored fluorescent compounds, some of which exhibit responses to the selected volatile organic compounds.

N-Allyl- N, N-Bis(trimethylsilyl)amine as a Novel Electrolyte Additive To Enhance the Interfacial Stability of a Ni-Rich Electrode for Lithium-Ion Batteries

Enhancing the electrode/electrolyte interface stability of high-capacity LiNi_0.8Co_0.15Al_0.05O₂ (LNCA) cathode material is urgently required for its application in next-generation lithium-ion battery. Herein, we demonstrate that enhanced interfacial stability of LNCA can be achieved by simply introducing 2 wt % N-allyl- N, N-bis(trimethylsilyl)amine (NNB) electrolyte additive. Electrolyte oxidation reactions and electrode structural destruction are greatly suppressed in the electrolyte with NNB additive, leading to improved cyclic stability of LNCA from 72.8 to 86.2% after 300 cycles. The mechanism of NNB on improving the cyclic stability of LNCA has been verified to its excellent solid electrolyte interface (SEI) film-forming capability. Moreover, the X-ray diffraction and X-ray photoelectron spectroscopy results indicate that the NNB-derived Si-containing SEI film restrains the Li/Ni disorder of LNCA during cycling, which further improves the cyclic stability of Ni-rich LNCA. Importantly, the charging/discharging test reveals that the NNB additive effectively improves the cyclic stability of the LNCA/graphite full cell.

Metallic Intermediate Phase Inducing Morphological Transformation in Thermal Nitridation: Ni3FeN-Based Three-Dimensional Hierarchical Electrocatalyst for Water Splitting

Transition-metal nitrides have attracted a great deal of interest as electrocatalysts for water splitting due to their super metallic performance, high efficiency, and good stability. Herein, we report a novel design of hierarchical electrocatalyst based on Ni₃FeN, where the presence of carbon fiber cloth as a scaffold can effectively alleviate the aggregation of Ni₃FeN nanostructure and form three-dimensional conducting networks to enlarge the surface area and simultaneously enhance the charge transfer. The composition and morphological variations of NiFe precursors during annealing in different atmospheres were investigated. Such Ni₃FeN/CC hierarchical electrocatalyst shows much improved electrochemical properties for water splitting in terms of overpotentials (105 and 190 mV at 10 mA/cm² for hydrogen evolution reaction and oxygen evolution reaction, respectively) and stability.

Core–shell structured hierarchically porous NiO microspheres with enhanced electrocatalytic activity for oxygen evolution reaction

We present a one-pot synthetic strategy to synthesize hierarchically porous NiO microspheres with enhanced activity for OER.

Improved Li-storage performance with PEDOT-decorated MnO2 nanoboxes

In this paper, MnO₂ nanoboxes coated with poly(3,4-ethylenedioxythiophene) film (denoted as MnO₂@PEDOT) are investigated as an anode material in lithium-ion batteries. The MnO₂ nanoboxes are developed through the surface chemical oxidation decomposition of MnCO₃ cubes and the subsequent removal of their remaining cores. PEDOT is coated on the surface of MnO₂ nanoboxes via in situ polymerization of 3,4-ethylenedioxythiophene. The charge-discharge tests demonstrate that this special configuration endows the resulting MnO₂@PEDOT with remarkable electrochemical performances, that is a reversible capacity of 628 mA h g^-1 after 850 cycles at a current density of 1000 mA g^-1 and a rate capacity of 367 mA h g^-1 at 3000 mA g^-1. The results indicate that the nanoboxes provide the paths for Li-ion diffusion, the reaction sites for Li-ion intercalation/deintercalation and the space to buffer the volume change during the charge-discharge process, while the conductive polymer ensures the structural stability and improves the electronic conductive property of MnO₂.

Solvothermal synthesis and enhanced photo-electrochemical performance of hierarchically structured strontium titanate micro-particles

Homogeneous powders of almost spherical particles of SrTiO₃ with diameters of about 1 μm and large surface areas of up to 186 m² g⁻¹ were obtained from a facile one-pot solvothermal synthesis.