An ultrafast nickel–iron battery from strongly coupled inorganic nanoparticle/nanocarbon hybrid materials

High-Rate and Ultra-Stable aqueous Zinc-Ion batteries enabled by Potassium-Infused ammonium vanadate nanosheets

Aqueous zinc-ion batteries (AZIBs), defined by low expenses, superior safety, and plentiful reserves, demonstrate tremendous development potential in energy storage systems at the grid scale. Whereas the cathode instability and the limited diffusion of Zn2+ have impeded the development of AZIBs. Herein, a high-performance K-NH4V4O10 (K-NVO) cathode with K+ doping synthesized successfully through one-step hydrothermal approach. Experiments and density functional theory (DFT) calculations indicate that K-NVO has Zn2+ diffusion pathways with lower barriers for smoother transport, and lower formation energy. The combination of the rapid Zn2+ diffusion and the stable structure results in outstanding electrochemical performance of K-NVO as demonstrated in tests. K-NVO cathode achieves a specific capacity of 406 mAh g-1 at 0.2 A g-1, maintains satisfactory cyclic stability with 81.6 % capacity retention after 1000 cycles at 5 A g-1, and possesses a high energy density of 350.9 Wh kg-1. Furthermore, confirmation of the zinc storage mechanism in K-NVO was carried out through Ex situ tests, such as XRD and XPS. This research contributes a unique perspective to the formulation of high-performance cathode materials for AZIBs.

Voltage-Controlled ON-OFF-Switching of Magnetoresistance in FeOx/Fe/Au Aerogel Networks

Voltage control of magnetoresistance (MR) in nanoscale three-dimensional (3D) geometries is interesting from a fundamental point of view and a promising route toward novel sensors and energy-efficient computing schemes. Magneto-ionic mechanisms are favorable for low-voltage control of magnetism and room-temperature operation, but magneto-ionic control of MR has been studied only for planar geometries so far. We synthesize a 3D nanomaterial with magneto-ionic functionality by electrodepositing an iron hydroxide/iron coating on a porous nanoscale gold network (aerogel). To enable maximum magneto-ionic ON-OFF-switching, the thickness of the coating is adjusted to a few nanometers by a self-terminating electrodeposition process. In situ magnetotransport measurements during electrolytic gating of these nanostructures reveal large reversible changes in MR, including ON-OFF-switching of MR, with a small applied voltage difference (1.72 V). This effect is related to the electrochemical switching between a ferromagnetic iron shell/gold core nanostructure (negative MR at the reduction voltage) and an iron oxide shell/gold core nanostructure (negligible MR at the oxidation voltage).

Constructing stable V2O5/V6O13 heterostructure interface with fast Zn2+ diffusion kinetics for ultralong lifespan zinc-ion batteries

Given their plentiful reserves, impressive safety features, and economical pricing, aqueous zinc - ion batteries (ZIBs) have positioned themselves as strong competitors to lithium - ion batteries. Yet, the scarcity of available cathode materials poses a challenge to their continued development. In this study, a V2O5/V6O13 heterostructure has been synthesized using a one - pot hydrothermal approach and employed as the cathode material for ZIBs. As evidenced by both experimental and theoretical findings, V2O5/V6O13 heterostructure delivers a rapid electrons and ions diffusion kinetics promoted by the stable interface and strong electronic coupling with significant charge transfer between V2O5 and V6O13, as well as a stable interface achieved by adjusting V - O bond length. Consequently, the optimized V2O5/V6O13 heterostructure cathode of ZIBs demonstrates exceptional capacity (338 mAh g-1 at 0.1 A g-1), remarkable cycling stability (92.96 % retained after 1400 cycles at 1 A g-1). Through comprehensive theoretical calculations and ex situ characterization, the kinetic analysis and storage mechanism of Zn2+ are thoroughly investigated, providing a solid theoretical foundation for the advancement of novel V - based cathode materials aimed at enhancing the performance of ZIBs.

Electrode Materials, Structural Design, and Storage Mechanisms in Hybrid Supercapacitors

Currently, energy storage systems are of great importance in daily life due to our dependence on portable electronic devices and hybrid electric vehicles. Among these energy storage systems, hybrid supercapacitor devices, constructed from a battery-type positive electrode and a capacitor-type negative electrode, have attracted widespread interest due to their potential applications. In general, they have a high energy density, a long cycling life, high safety, and environmental friendliness. This review first addresses the recent developments in state-of-the-art electrode materials, the structural design of electrodes, and the optimization of electrode performance. Then we summarize the possible classification of hybrid supercapacitor devices, and their potential applications. Finally, the fundamental theoretical aspects, charge-storage mechanism, and future developing trends are discussed. This review is intended to provide future research directions for the next generation of high-performance energy storage devices.

Tendency Regulation of Competing Reactions Toward Highly Reversible Tin Anode for Aqueous Alkaline Batteries

Investigating dendrite-free stripping/plating anodes is highly significant for advancing the practical application of aqueous alkaline batteries. Sn has been identified as a promising candidate for anode material, but its deposition/dissolution efficiency is hindered by the strong electrostatic repulsion between Sn(OH)3 - and the substrate. Herein, this work constructs a nondense copper layer which serves as stannophile and hydrogen evolution inhibitor to adjust the tendency of competing reactions on Sn foil surface, thus achieving a highly reversible Sn anode. The interactions between the deposited Sn and the substrates are also strengthened to prevent shedding. Notably, the ratio of Sn redox reaction is significantly boosted from ≈20% to ≈100%, which results in outstanding cycling stability over 560 h at 10 mA cm-2 . A Sn//Ni(OH)2 battery device is also demonstrated with capacities from 0.94 to 22.4 mA h cm-2 and maximum stability of 1800 cycles.

Uniform Fe2 O3 Nanospheres Anchored on Multilayer Graphene as Anode Materials for High-Rate Ni-Fe Batteries

Ni-Fe battery is one of prospective aqueous alkaline batteries due to its high safety, eco-friendliness and cost-effectiveness. However, the electrochemical performance of Fe-based anodes is limited due to the particle aggregation and low electric conductivity. In this work, iron powder is used as a precursor in a chemical bath deposition method. By optimizing the concentration of HNO3 , a balanced dissolution-crystallization process is achieved to obtain uniform Fe2 O3 nanospheres in size between 60 and 90 nm, which are separately anchored on ultrasonically prepared multilayer graphene (MLG). This composite delivers specific discharge capacities of 191.1 and 160.8 mAh g-1 at the current densities of 2 and 10 A g-1 , respectively. A Ni-Fe battery with the as-prepared Fe2 O3 /MLG as anode and Ni(OH)2 /MLG as cathode exhibits an energy density of 69.5 Wh kg-1 at a high power density of 3931.6 W kg-1 .

Ultrafast Electrical Pulse Synthesis of Highly Active Electrocatalysts for Beyond-Industrial-Level Hydrogen Gas Batteries

The high reliability and proven ultra-longevity make aqueous hydrogen gas (H2 ) batteries ideal for large-scale energy storage. However, the low alkaline hydrogen evolution and oxidation reaction (HER/HOR) activities of expensive platinum catalysts severely hamper their widespread applications in H2 batteries. Here, cost-effective, highly active electrocatalysts, with a model of ruthenium-nickel alloy nanoparticles in ≈3 nm anchored on carbon black (RuNi/C) as an example, are developed by an ultrafast electrical pulse approach for nickel-hydrogen gas (NiH2 ) batteries. Having a competitive low cost of about one fifth of Pt/C benckmark, this ultrafine RuNi/C catalyst displays an ultrahigh HOR mass activity of 2.34 A mg-1 at 50 mV (vs RHE) and an ultralow HER overpotential of 19.5 mV at a current density of 10 mA cm-2 . As a result, the advanced NiH2 battery can efficiently operate under all-climate conditions (from -25 to +50 °C) with excellent durability. Notably, the NiH2 cell stack achieves an energy density up to 183 Wh kg-1 and an estimated cost of ≈49 $ kWh-1 under an ultrahigh cathode Ni(OH)2 loading of 280 mg cm-2 and a low anode Ru loading of ≈62.5 µg cm-2 . The advanced beyond-industrial-level hydrogen gas batteries provide great opportunities for practical grid-scale energy storage applications.

High-Energy Sn-Ni and Sn-Air Aqueous Batteries via Stannite-Ion Electrochemistry

Tin is promising for aqueous batteries (ABs) due to its multiple electrons' reactions, high corrosion resistance, large hydrogen overpotential, and excellent environmental compatibility. However, restricted to the high thermodynamic barrier and the poor electrochemical kinetics, efficient alkaline Sn plating/stripping at facile conditions has not yet been realized. Here, for the first time, we demonstrate a highly reversible stannite-ion electrochemistry and construct a novel paradigm of high-energy Sn-based ABs. Combined spectroscopic characterization, electrochemical evaluation, and theoretical computation reveal the thermodynamic merits with a low reaction energy barrier and feasible H₂O participation in Sn-ion reduction as well as the kinetic merits with fastened surface charge transfer and SnO₂^2- diffusion. The resultant alkaline Sn anode delivers a low potential of -1.07 V vs Hg/HgO, a specific capacity of 450 mA h g^-1, a Coulombic efficiency of near 100%, superb rate capability at 45.5 A g^-1, and excellent cycling durability without dendrite and dead Sn. As a proof of concept, we developed new high-energy Sn-based ABs, including 1.45 V Sn-Ni with 314 W h kg^-1 (58 kW kg^-1 and over 15,000 cycles) and 1.0 V Sn-air with 420 W h kg^-1 (lifespan over 1900 h), on the basis of masses from cathode and anode active materials. The findings prove the feasibility of the alkaline Sn metal anode, and the new suite of high-energy Sn-based ABs may be of immediate benefit toward safe, reliable, and affordable energy storage.

Metal Oxide Nanosheet: Synthesis Approaches and Applications in Energy Storage Devices (Batteries, Fuel Cells, and Supercapacitors)

In recent years, the increasing energy requirement and consumption necessitates further improvement in energy storage technologies to obtain high cycling stability, power and energy density, and specific capacitance. Two-dimensional metal oxide nanosheets have gained much interest due to their attractive features, such as composition, tunable structure, and large surface area which make them potential materials for energy storage applications. This review focuses on the establishment of synthesis approaches of metal oxide nanosheets (MO nanosheets) and their advancements over time, as well as their applicability in several electrochemical energy storage systems, such as fuel cells, batteries, and supercapacitors. This review provides a comprehensive comparison of different synthesis approaches of MO nanosheets, as well their suitability in several energy storage applications. Among recent improvements in energy storage systems, micro-supercapacitors, and several hybrid storage systems are rapidly emerging. MO nanosheets can be employed as electrode and catalyst material to improve the performance parameters of energy storage devices. Finally, this review outlines and discusses the prospects, future challenges, and further direction for research and applications of metal oxide nanosheets.

Analytical Investigation of Iron-Based Stains on Carbonate Stones: Rust Formation, Diffusion Mechanisms, and Speciation

In cultural heritage, unaesthetic stains on carbonate stones due to their close contacts with metals are of concern for the preservation of sculptures, monumental facades and archeological finds of various origin and antiquities. Rust stains made up of various oxidized iron compounds are the most frequent forms of alteration. The presence of ferric iron on rust-stained marble surfaces was confirmed in previous studies and oriented the choice of the best cleaning method (based on complexing agents specific for ferric ions). However, the composition of rust stains may vary along their extension. As the corrosion of the metallic iron proceeds, if the oxygen levels in the surroundings are low and there are no conditions to favor the oxidation, ferrous ions can also diffuse within the carbonate structure and form a variety of intermediate compounds. In this study, the iron stains on archeological marbles were compared with those artificially produced on Carrara marbles and Travertine samples. The use of integrated techniques (optical and scanning electron microscopy as well as Mössbauer and XPS spectroscopy) with complementary analytical depths, has provided the overall information. Rust formation and diffusion mechanisms in carbonates were revealed together with the evolution of iron speciation and identification of phases such as ferrihydrite, goethite, maghemite, nanomagnetite, and hematite.

Efficient electrocatalytic valorization of chlorinated organic water pollutant to ethylene

Electrochemistry can provide an efficient and sustainable way to treat environmental waters polluted by chlorinated organic compounds. However, the electrochemical valorization of 1,2-dichloroethane (DCA) is currently challenged by the lack of a catalyst that can selectively convert DCA in aqueous solutions into ethylene. Here we report a catalyst comprising cobalt phthalocyanine molecules assembled on multiwalled carbon nanotubes that can electrochemically decompose aqueous DCA with high current and energy efficiencies. Ethylene is produced at high rates with unprecedented ~100% Faradaic efficiency across wide electrode potential and reactant concentration ranges. Kinetic studies and density functional theory calculations reveal that the rate-determining step is the first C-Cl bond breaking, which does not involve protons-a key mechanistic feature that enables cobalt phthalocyanine/carbon nanotube to efficiently catalyse DCA dechlorination and suppress the hydrogen evolution reaction. The nanotubular structure of the catalyst enables us to shape it into a flow-through electrified membrane, which we have used to demonstrate >95% DCA removal from simulated water samples with environmentally relevant DCA and electrolyte concentrations.

High-Performance Biscrolled Ni-Fe Yarn Battery with Outer Buffer Layer

The increasing demand for portable and wearable electronics has promoted the development of safe and flexible yarn-based batteries with outstanding electrochemical properties. However, achieving superior energy storage performance with a high active material (AM) load and long cycle life with this device format remains a challenge. In this study, a stable and rechargeable high-performance aqueous Ni-Fe yarn battery was constructed via biscrolling to embed AMs within helical carbon nanotube (CNT) yarn corridors. Owing to the high load of charge storage nanoparticles (NPs; above 97 wt%) and the outer neat CNT layer, the buffered biscrolled Ni-Fe yarn battery demonstrates excellent linear capacity (0.053 mAh/cm) and cycling stability (60.1% retention after 300 charge/discharge cycles) in an aqueous electrolyte. Moreover, our flexible yarn battery exhibits maximum energy/power densities of 422 mWh/cm³ and 7535 mW/cm³ based on the total volume of the cathode and anode, respectively, which exceed those reported for many flexible Ni-Fe batteries. Thus, biscrolled Ni-Fe yarn batteries are promising candidates for next-generation conformal energy solutions.

Rechargeable Batteries for Grid Scale Energy Storage

Ever-increasing global energy consumption has driven the development of renewable energy technologies to reduce greenhouse gas emissions and air pollution. Battery energy storage systems (BESS) with high electrochemical performance are critical for enabling renewable yet intermittent sources of energy such as solar and wind. In recent years, numerous new battery technologies have been achieved and showed great potential for grid scale energy storage (GSES) applications. However, their practical applications have been greatly impeded due to the gap between the breakthroughs achieved in research laboratories and the industrial applications. In addition, various complex applications call for different battery performances. Matching of diverse batteries to various applications is required to promote practical energy storage research achievement. This review provides in-depth discussion and comprehensive consideration in the battery research field for GSES. The overall requirements of battery technologies for practical applications with key parameters are systematically analyzed by generating standards and measures for GSES. We also discuss recent progress and existing challenges for some representative battery technologies with great promise for GSES, including metal-ion batteries, lead-acid batteries, molten-salt batteries, alkaline batteries, redox-flow batteries, metal-air batteries, and hydrogen-gas batteries. Moreover, we emphasize the importance of bringing emerging battery technologies from academia to industry. Our perspectives on the future development of batteries for GSES applications are provided.

Stochastic Local Breakdown of Oxide Film on Ni from Identical-Location Imaging: One Single Site at a Time

The electrochemical breakdown of a metal oxide film can directly affect the performance of functional electrochemical devices. However, revealing the structural insight into the breakdown sites is challenging because of heterogeneity: different breakdown sites are spatially distributed over the surface. Herein, we combine scanning electrochemical cell microscopy with identical-location microscopies to reveal the heterogeneity in the breakdown of NiO film on Ni in a site-by-site manner. Local critical breakdown potential varies by ∼500 mV, corresponding to an excess energy of 0.02-0.12 J/m². Correlative composition imaging using time-of-flight secondary ion mass spectrometry shows Ni crystal grains with thinner NiO films are more resistant to breakdown. This high resistance is explained using classical nucleation theory, where the electrical energy is affected by the film thickness through the local interfacial capacitance. The correlative imaging approach overcomes the issue of heterogeneity, providing conclusive insight into the stability of the electrochemical interfaces.

Revitalizing Iron Redox by Anion-Insertion-Assisted Ferro- and Ferri-Hydroxides Conversion at Low Alkalinity

Iron hydroxides are desirable alkaline battery electrodes for low cost and environmental beneficence. However, hydrogen evolution on charging and Fe₃O₄ formation on discharging cause low storage capacity and poor cycling life. We report that green rust (GR) (Fe²⁺₄Fe³⁺₂ (HO^-)₁₂SO₄), formed via sulfate insertion, promotes Fe(OH)₂/FeOOH conversion and shows a discharge capacity of ∼211 mAh g^-1 in half-cells and Coulombic efficiency of 93% after 300 cycles in full-cells. Theoretical calculations show that Fe(OH)₂/FeOOH conversion is facilitated by intercalated sulfate anions. Classical molecular dynamics simulations reveal that electrolyte alkalinity strongly impacts the energetics of sulfate solvation, and low alkalinity ensures fast transport of sulfate ions. Anion-insertion-assisted Fe(OH)₂/FeOOH conversion, also achieved with Cl^- ion, paves a pathway toward efficient utilization of Fe-based electrodes for sustainable applications.

Metal-Organic Framework-Based Materials for Aqueous Zinc-Ion Batteries: Energy Storage Mechanism and Function

Aqueous rechargeable zinc-ion batteries (ZIBs) featuring competitive performance, low cost and high safety hold great promise for applications in grid-scale energy storage and portable electronic devices. Metal-organic frameworks (MOFs), relying on their large framework structure and abundant active sites, have been identified as promising materials in ZIBs. This review comprehensively presents the current development of MOF-based materials including MOFs and their derivatives in ZIBs, which begins with Zn storage mechanism of MOFs, followed by introduction of various types of MOF-based cathode materials (PB and PBA, Mn-based MOF, V-based MOF, conductive MOF and their derivatives), and the regulation approaches for Zn deposition behavior. The key factors and optimization strategies of MOF-based materials that affect ZIBs performance are emphasized and discussed. Finally, the challenges and further research directions of MOF-based materials for advanced zinc-ion batteries are provided.

Intrinsic Carbon Defects Induced Reversible Antimony Chemistry for High-Energy Aqueous Alkaline Batteries

Developing high-capacity, dendrite-free, and stable anode materials for robust aqueous alkaline batteries (AABs) is an ongoing challenge. Antimony (Sb) is predicated as an attractive anode material, but it still suffers from low capacity and poor stability caused by the obstructed kinetic behavior and uncontrollable nucleation for SbO₂ ^- . Herein, designing a new defect-modified carbon skeleton (D-CS), a highly reversible Sb anode with ultralong cycling stability is realized at practical levels of capacity and high depth of discharge (DOD). The abundant intrinsic carbon defects can effectively form positive charge centers to weaken electrostatic repulsion between SbO₂ ^- and electrode surface, facilitating the fast ion kinetics and provide generous controllable nucleation sites. In addition, the uniform electric field distribution of the D-CS induces manageable plating and stripping of the Sb metal, which effectively boosts its electrochemical reversibility and restrains adverse reactions. Accordingly, the Sb/D-CS electrode achieves a long cycle life of over 500 h with a capacity of 2 mAh cm^-2 . Even at an ultrahigh capacity of 10 mAh cm^-2 , it can still work stably up to 40 h. Furthermore, its feasibility as advanced anode in AABs is also confirmed by assembled Ni//Sb/D-CS full batteries with an ultrahigh capacity of 13.5 mAh cm^-2 and a considerable stability of 4500 cycles.

Synergistic dual conversion reactions assisting Pb-S electrochemistry for energy storage

Based on the analysis of three thermodynamic parameters of various M-S systems (solubility of metal sulfides [M_xS_y] in aqueous solution, volume change of the metal-sulfur [M-S] battery system, and the potential of S/M_xS_y cathode redox couple), an aqueous Pb-S battery operated by synergistic dual conversion reactions (cathode: S⇄PbS, anode: Pb²⁺⇄PbO₂) has been officially reported. Benefitting from the inherent insolubility of PbS and a conversion-type counter electrode, the aqueous Pb-S battery exhibited two advantages: it is shuttle effect free and has a dendrite-free nature. Moreover, the practical value of the Pb-S battery was further certified by the prototype S|Pb(NO₃)₂ǁZn(NO₃)₂|Zn hybrid cell, which afforded an energy density of 930.9 Wh kg⁻¹_sulfur.

As one of the most promising cathode materials for next-generation batteries, sulfur has been widely used in organic metal-sulfur batteries, especially in Li-S batteries. However, to date, Pb-S chemistry has never been officially reported. In this paper, a reliable aqueous Pb-S battery based on a dual conversion reaction was constructed. To clarify the feasibility, three important thermodynamic parameters of the Pb-S system were analyzed, including the solubility of PbS in aqueous solution, the volume change of the Pb-S battery system, and the potential of the S/PbS cathode redox couple. Here, it is demonstrated that the aqueous Pb-S battery possesses a great advantage in theory, and the inherent insolubility of PbS makes an aqueous Pb-S system without a shuttle effect. Moreover, the conversion-type counter electrode of a Pb-S system with a stable nucleation rate endows it with a dendrite-free nature, which is quite different from the traditional metal-sulfur battery with a stripping/plating–type counter electrode. Benefitting from these remarkable natures, the aqueous Pb-S battery exhibits a high discharge capacity of 1,343.9 mAh g⁻¹_sulfur with a capacity retention of 71.4% after 400 cycles. In addition, the feasibility of this Pb-S system is further demonstrated in a hybrid cell consisting of an S cathode and Zn anode, which affords an energy density of 930.9 Wh kg⁻¹_sulfur.

Connecting battery technologies for electric vehicles from battery materials to management

Vehicle electrification has always been a hot topic and gradually become a major role in the automobile manufacturing industry over the last two decades. This paper presented comprehensive discussions and insightful evaluations of both conventional electric vehicle (EV) batteries (such as lead-acid, nickel-based, lithium-ion batteries, etc.) and the state-of-the-art battery technologies (such as all-solid-state, silicon-based, lithium-sulphur, metal-air batteries, etc.). Battery major component materials, operating characteristics, theoretical models, manufacturing processes, and end-of-life management were thoroughly reviewed. Different from other reviews focusing on theoretical studies, this review emphasized the key aspects of battery technologies, commercial applications, and lifecycle management. Useful battery managing technologies such as health prediction, charging and discharging, as well as thermal runaway prevention were thoroughly discussed. Two novel hexagon radar charts of all-round evaluations of most reigning and potential EV battery technologies were created to predict the development trend of the EV battery technologies. It showed that lithium-ion batteries (3.9 points) would be still the dominant product for the current commercial EV power battery market in a short term. However, some cutting-edge technologies such as an all-solid-state battery (3.55 points) and silicon-based battery (3.3 points) are highly likely to be the next-generation EV onboard batteries with both higher specific power and better safety performance.

Interconnecting 3D Conductive Networks with Nanostructured Iron/Iron Oxide Enables a High-Performance Flexible Battery

Aqueous Ni/Fe alkaline batteries with features of low cost and high safety show great potential for application in portable and wearable electronics. However, the poor kinetics of the Fe-based anode greatly limits the large-scale applications of Ni/Fe batteries. Herein, we report an interconnected 3D conductive network with carbon-coated nanostructured iron/iron oxide (3D-Fe/Fe₂O₃@C) as an efficient anode for a flexible Ni/Fe battery. A hydrogel precursor is used to molecularly link and confine Fe³⁺ to spatial networks, resulting in a uniform dispersion of Fe/Fe₂O₃-heterostructured nanoparticles. Theoretical investigations reveal regulated potential loss and improved delocalized carrier density as a result of carbon coating and the mixed metal/metal oxide structure. In addition to these merits, due to the regulated wettability and electroactive surface areas, the 3D-Fe/Fe₂O₃@C anode with a high mass loading delivers an extraordinary areal capacity of 3.07 mA h cm^-2, as well as the boosted rate capability and Coulombic efficiency. When coupled with the NiCo₂O₄ cathode, the flexible quasi-solid-state Ni/Fe battery exhibits an admirable energy density of 15.53 mW h cm^-3 and a maximum power density of 761.91 W h cm^-3. The good stability after 20,000 cycles and severe mechanical deformations of the as-fabricated Ni/Fe battery imply it as a promising flexible energy storage device for practical applications.

Metal-Organic Frameworks-Derived Self-Supported Carbon-Based Composites for Electrocatalytic Water Splitting

Electrocatalytic water splitting has been considered as a promising strategy for the sustainable evolution of hydrogen energy and storage of intermittent electric energy. Efficient catalysts for electrocatalytic water splitting are urgently demanded to decrease the overpotentials and promote the sluggish reaction kinetics. Carbon-based composites, including heteroatom-doped carbon materials, metals/alloys@carbon composites, metal compounds@carbon composites, and atomically dispersed metal sites@carbon composites have been widely used as the catalysts due to their fascinating properties. However, these electrocatalysts are almost powdery form, and should be cast on the current collector by using the polymeric binder, which would result in the unsatisfied electrocatalytic performance. In comparison, a self-supported electrode architecture is highly attractive. Recently, self-supported metal-organic frameworks (MOFs) constructed by coordination of metal centers and organic ligands have been considered as suitable templates/precursors to construct free-standing carbon-based composites grown on conductive substrate. MOFs-derived carbon-based composites have various merits, such as the well-aligned array architecture and evenly distributed active sites, and easy functionalization with other species, which make them suitable alternatives to non-noble metal-included electrocatalysts. In this review, we intend to show the research progresses by employment of MOFs as precursors to prepare self-supported carbon-based composites. Focusing on these MOFs-derived carbon-based nanomaterials, the latest advances in their controllable synthesis, composition regulation, electrocatalytic performances in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting (OWS) are presented. Finally, the challenges and perspectives are showed for the further developments of MOFs-derived self-supported carbon-based nanomaterials in electrocatalytic reactions.

Neutron Diffraction Study of a Sintered Iron Electrode In Operando

Iron is a promising, earth-abundant material for future energy applications. In this study, we use a neutron diffractometer to investigate the properties of an iron electrode in an alkaline environment. As neutrons penetrate deeply into materials, neutron scattering gives us a unique insight into what is happening inside the electrode. We made our measurements while the electrode was charging or discharging. Our key questions are: Which phases occur for the first and second discharge plateaus? And why are iron electrodes less responsive at higher discharge rates? We conclude that metallic iron and iron hydroxide form the redox pair for the first discharge plateau. For the second discharge plateau, we found a phase similar to feroxyhyte but with symmetrical and equally spaced arrangement of hydrogen atoms. The data suggest that no other iron oxide or iron (oxy)hydroxide formed. Remarkable findings include the following: (1) substantial amounts of iron hydroxide are always present inside the electrode. (2) Passivation is mostly caused by iron hydroxide that is unable to recharge. (3) Iron fractions change as expected, while iron hydroxide fractions are delayed, resulting in substantial amounts of amorphous, undetectable iron phases. About 40% of the participating iron of the first plateau and about 55% of the participating iron for the second plateau are undetectable. (4) Massive and unexpected precipitation of iron hydroxide occurs in the transition from discharging to charging. (2), (3), and (4) together cause accumulation of iron hydroxide inside the electrode.

Heterogeneous Molecular Catalysts of Metal Phthalocyanines for Electrochemical CO2 Reduction Reactions

ConspectusMolecular catalysts, often deployed in homogeneous conditions, are favorable systems for structure-reactivity correlation studies of electrochemical reactions because of their well-defined active site structures and ease of mechanistic investigation. In pursuit of selective and active electrocatalysts for the CO2 reduction reactions which are promising for converting carbon emissions to useful fuels and chemical products, it is desirable to support molecular catalysts on substrates because heterogeneous catalysts can afford the high current density and operational convenience that practical electrolyzers require. Herein, we share our understanding in the development of heterogenized metal phthalocyanine catalysts for the electrochemical reduction of CO2. From the optimization of preparation methods and material structures for the electrocatalytic activity toward CO2 reduction to CO, we find that molecular-level dispersion of the active material and high electrical conductivity of the support are among the most important factors controlling the activity. The molecular nature of the active site enables mechanism-based optimization. We demonstrate how electron-withdrawing and -donating ligand substituents can be utilized to modify the redox property of the molecule and improve its catalytic activity and stability. Adjusting these factors further allows us to achieve electrochemical reduction of CO2 to methanol with appreciable activity, which has not been attainable by conventional molecular catalysts. The six-electron reduction process goes through CO as the key intermediate. Rapid and continuous electron delivery to the active site favors further reduction of CO to methanol. We also point out that, in homogeneous electrocatalysis where the catalyst molecules are dissolved in the electrolyte solution, even if the molecular structure remains intact, the actual catalysis may be dominated by molecules permanently adsorbed on the electrode surface and is thus heterogeneous in nature. This account uses our research on CO2 electroreduction reactions catalyzed by metal phthalocyanine molecules to illustrate our understanding about heterogeneous molecular electrocatalysis, which is also applicable to other electrochemical systems.

Anticatalytic Strategies to Suppress Water Electrolysis in Aqueous Batteries

Aqueous electrolytes are the leading candidate to meet the surging demand for safe and low-cost storage batteries. Aqueous electrolytes facilitate more sustainable battery technologies due to the attributes of being nonflammable, environmentally benign, and cost effective. Yet, water's narrow electrochemical stability window remains the primary bottleneck for the development of high-energy aqueous batteries with long cycle life and infallible safety. Water's electrolysis leads to either hydrogen evolution reaction (HER) or oxygen evolution reaction (OER), which causes a series of dire consequences, including poor Coulombic efficiency, short device longevity, and safety issues. These are often showstoppers of a new aqueous battery technology besides the low energy density. Prolific progress has been made in the understanding of HER and OER from both catalysis and battery fields. Unfortunately, a systematic review on these advances from a battery chemistry standpoint is lacking. This review provides in-depth discussions on the mechanisms of water electrolysis on electrodes, where we summarize the critical influencing factors applicable for a broad spectrum of aqueous battery systems. Recent progress and existing challenges on suppressing water electrolysis are discussed, and our perspectives on the future development of this field are provided.

High-capacity and high-rate Ni-Fe batteries based on mesostructured quaternary carbon/Fe/FeO/Fe3O4 hybrid material

The Ni-Fe battery is a promising alternative to lithium ion batteries due to its long life, high reliability, and eco-friendly characteristics. However, passivation and self-discharge of the iron anode are the two main issues. Here, we demonstrate that controlling the valence state of the iron and coupling with carbon can solve these problems. We develop a mesostructured carbon/Fe/FeO/Fe₃O₄ hybrid by a one-step solid-state reaction. Experimental evidence reveals that the optimized system with three valence states of iron facilitates the redox kinetics, while the carbon layers can effectively enhance the charge transfer and suppress self-discharge. The hybrid anode exhibits high specific capacity of 604 mAh⋅g⁻¹ at 1 A⋅g⁻¹ and high cyclic stability. A Ni-Fe button battery is fabricated using the hybrid anode exhibits specific device energy of 127 Wh⋅kg⁻¹ at a power density of 0.58 kW⋅kg⁻¹ and maintains good capacity retention (90%) and coulombic efficiency (98.5%).

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A quaternary hybrid has been fabricated by a one-step solid-state reaction.

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Controlling the valence state of iron facilitates redox kinetics and charge transfer.

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The hybrid anode exhibits high specific capacity of 604 mAh⋅g⁻¹ at 1 A⋅g⁻¹.

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The NiFe battery exhibits specific energy of 127 Wh⋅kg⁻¹ and superior durability.

Understanding Excess Li Storage beyond LiC6 in Reduced Dimensional Scale Graphene

A phenomenon is observed in which the electrochemical performances of porous graphene electrodes show unexpectedly increasing capacities in the Li storage devices. However, despite many studies, the cause is still unclear. Here, we systematically present the reason for the capacity enhancements of the pristine graphene anode under functional group exclusion through morphological control and crystal structure transformation. The electrochemical synergy of both the edge effect and surface effect of the reduced dimensional scale graphene in an open-porous structure facilitates significantly enhanced capacity through multidimensional Li-ion accessibility and accumulation of Li atoms. Furthermore, the Stone-Wales defects boosted during Li insertion and extraction promote a capacity elevation beyond the theoretical capacity of the carbon electrode even after long-term cycles at high C-rates. As a result, the morphologically controlled graphene anode delivers the highest reversible capacity of 3074 mA h g^-1 with a 163% capacity increase after 2000 cycles at 5 C. It also presents a gradually increasing capacity up to 1102 mA h g^-1 even at 50 C without an evident capacity fading tendency. This study provides valuable information into the practical design of ultralight and high-rate energy storage devices.

Oxygen-rich interface enables reversible stibium stripping/plating chemistry in aqueous alkaline batteries

Aqueous alkaline batteries see bright future in renewable energy storage and utilization, but their practical application is greatly challenged by the unsatisfactory performance of anode materials. Herein, we demonstrate a latent Sb stripping/plating chemistry by constructing an oxygen-rich interface on carbon substrate, thus providing a decent anode candidate. The functional interface effectively lowers the nucleation overpotential of Sb and strengthens the absorption capability of the charge carriers (SbO₂⁻ ions). These two advantageous properties inhibit the occurrence of side reactions and thus enable highly reversible Sb stripping/plating. Consequently, the Sb anode delivers theoretical-value-close specific capacity (627.1 mA h g⁻¹), high depth of discharge (95.0%) and maintains 92.4% coulombic efficiency over 1000 cycles. A robust aqueous NiCo₂O₄//Sb device with high energy density and prominent durability is also demonstrated. This work provides a train of thoughts for the development of aqueous alkaline batteries based on Sb chemistry.

The practical application of aqueous alkaline battery is confined by limited choice of anode. Here, the authors demonstrate an oxygen-rich interface induced reversible Sb stripping/plating chemistry that provides a promising Sb metal anode with fast reaction kinetics and favourable stability.

Hierarchical 3D Oxygenated Cobalt Vanadium Selenide Nanosheets as Advanced Electrode for Flexible Zinc-Cobalt and Zinc-Air Batteries

Highly flexible quasi solid-state batteries are promising in next-generation energy storage sectors due to their high energy density, power density, and low manufacturing cost. However, poor cycle life seriously limits their application in industrial sectors. Herein, a novel strategy is established to design the oxygenated cobalt vanadium selenide (O-Co_x V_{1- x} Se₂ ) nanostructures for high-performance quasi solid-state (QSS) zinc-cobalt batteries (ZCBs) and zinc-air batteries (ZABs). Density functional theory (DFT) calculation reveals that the doping effect of Co²⁺ into O-VSe₂ nanostructure could increase the density of states near the edge of the conduction band, demonstrating ultrafast electron transport kinetics. Most interestingly, the optimal O-Co_0.33 V_0.67 Se₂ cathode-based QSS-ZCB exhibits an ultrahigh specific capacity of 422.7 mAh g^-1 at a current density of 1 A g^-1 , excellent energy density of 186.4 Wh kg^-1 , tremendous power density of 5.65 kW kg^-1 , and ultralong cycle life (86.9% capacity retention after 3000 cycles). Furthermore, O-Co_0.33 V_0.67 Se₂ air-cathode based QSS-ZAB delivers a peak power density of 162 mW cm^-2 and ultralong cycle life over 100 h. These experimental and theoretical studies indicate that the electrochemically induced, cobalt stabilizes the vanadium is essential to boost the energy storage properties and cycle life of both ZCBs and ZABs.

Ultrathin nickel manganese nanosheets with rich oxygen-vacancy as a durability electrode for aqueous Ni//Zn batteries

Advanced aqueous batteries with abundant global reserves, large discharge capacity and long life span are crucial research objectives. Herein, a kind of aqueous Zn-ion battery was fabricated with ultra-thin Ni-Mn nanosheet electrode and zinc foil. A simple H₂-annealing process was employed to handle the NiMn_xO_y nanosheets to form oxygen vacancy. Based on the formation of fast ion diffusion channels and the increase of active sites, the fabricated H-NiMn_xO_y nanosheet electrode displays an areal capacity of 0.68 mA h cm^-2 at a current density of 2 mA cm^-2 and an excellent cycling performance (almost no reduction after 6000 cycles). The fabricated H-NiMn_xO_y//Zn battery obtains a high areal capacity, up to 0.66 mA h cm^-2 at a current density of 4 mA cm^-2, and shows a long cycling stability (88.5% capacity retention after 5500 cycles). In particular, it has a high energy density, up to 1.13 mW cm^-2 at a power density of 3.34 mW cm^-2, more than many other similar devices. Thus, this research provides a new idea for the wide application of aqueous Zn-ion battery in intelligent equipment and electric vehicles.

3D Printed Compressible Quasi-Solid-State Nickel-Iron Battery

The design of a compressible battery with stable electrochemical performance is extremely important in compression-tolerant and flexible electronics. While this remains challenging with the current battery manufacturing method, the field of 3D printing offers the possibility of producing free-standing 3D-printed electrodes with various structural configurations. Through the simple and scalable strategy, various structural configurations can be produced. Herein, we demonstrate a 3D-printed quasi-solid-state Ni-Fe battery (QSS-NFB) that shows excellent compressibility, ultrahigh energy density, and superior long-term cycling durability. Through a rational design and adjustment of chemical components, two electrodes consisting of ultrathin Ni(OH)₂ nanosheet array cathode and holey α-Fe₂O₃ nanorod array anode are achieved with a ultrahigh active material loading over 130 mg cm^-3 and excellent compressibility up to 60%. It is noteworthy that the compressible QSS-NFB demonstrated an excellent cycling stability (∼91.3% capacity retentions after 10000 cycles) and ultrahigh energy density (28.1 mWh cm^-3 at a power of 10.6 mW cm^-3). This work provides a simple method for producing compression-tolerant energy-storage devices, which are expected to have promising applications in next generation stretchable/wearable electronics.

Hierarchical NiSe2 Nanosheet Arrays as a Robust Cathode toward Superdurable and Ultrafast Ni-Zn Aqueous Batteries

Zn-based aqueous batteries are enjoying the hotspots of worldwide research as their significant merits in economic cost and safety. However, the lack of a robust cathode (positive electrode) owning excellent rate ability, high capacity, and stability challenges their practical application. Herein, we propose hierarchical NiSe₂ nanosheet arrays as a robust cathode toward high-performance Ni-Zn aqueous batteries. Attributed to in situ anion exchange and Kirkendall effects, the nanosheet arrays are hierarchically constructed by NiSe₂ nanoparticles and abundant mesopores, which fully expose the active sites and accelerate the electrode kinetics. This unique structure endows the NiSe₂ electrode with remarkable specific capacity (245.1 mAh g^-1) and extraordinary high-rate ability (maintains 58% at 72.8 A g^-1) together with 10,000 cycles without any obvious capacity degeneration. As a result, based on the total active weight, our NiSe₂//Zn battery is capable of record-high power density (91.22 kW kg^-1/639.1 mW cm^-2), imposing energy density (328.8 Wh kg^-1/2.303 mWh cm^-2), and ultralong lifespan (only 8.3% capacity loss after 10,000 cycles), surpassing most of the aqueous batteries and supercapacitors recently reported. Moreover, this NiSe₂//Zn battery is also affordable (US$40 per kWh) and safe. These results open a new avenue for developing superdurable and ultrafast high-energy Ni-Zn batteries toward affordable and practical energy storage.

Configuring hierarchical Ni/NiO 3D-network assisted with bamboo cellulose nanofibers for high-performance Ni-Zn aqueous batteries

The further application of Ni-Zn aqueous batteries is majorly restricted by nickel-based cathodes due to their low capacity and poor cycling stability, which requires the development of hierarchically nanostructured nickel and nickel oxides. Herein, we prepare a novel nickel-based electrode with hierarchical 3D networks by configuring nanostructured Ni and Ni/NiO nanoparticles onto bamboo-derived cellulose nanofibers (denoted as Ni/NiO-BCF). Owing to the high conductivity of carbonized nanofibers and enhanced Ni/NiO active sites exposed, the Ni/NiO-BCF electrode delivers a capacity of 248 mA h g^-1 at 0.625 A g^-1 and exhibits a good cycling stability (94.5% after 2000 cycles). The as-fabricated Ni/NiO-BCF//Zn battery shows a high capacity of 296 mA h g^-1 at 0.625 A g^-1 and excellent cycling stability (almost no decay after 1000 cycles). Notably, a peak energy density of 313.4 W h kg^-1 is also achieved from the Ni/NiO-BCF//Zn battery. This work provides novel insights into developing elaborately-nanostructured electrodes from natural and sustainable resources for high-capacity and long-cycle energy storage systems.

Superstructured α-Fe2O3 nanorods as novel binder-free anodes for high-performing fiber-shaped Ni/Fe battery

Fiber-shaped energy storage devices areindispensableparts of wearable and portable electronics. Aqueous rechargeable Ni/Fe battery is a very appropriate energy storage device due to their good safety without organic electrolytes, high ionic conductivity, and low cost. Unfortunately, the low energy density, poor power density and cycling performance hinder its further practical applications. In this study, in order to obtain high performance negative iron-based material, we first synthesized α-iron oxide (α-Fe₂O₃) nanorods (NRs) with superstructures on the surface of highly conductive carbon nanotube fibers (CNTFs), then electrically conductive polypyrrole (PPy) was coated to enhance the electron, ion diffusion and cycle stability. Theas-prepared α-Fe₂O₃@PPy NRs/CNTF electrode shows a high specific capacity of 0.62 Ah cm^-3 at the current density of 1 A cm^-3. Furthermore, the Ni/Fe battery that was assembled by the above negative electrode shows a maximum volumetric energy density of 15.47 mWh cm^-3 with 228.2 mW cm^-3 at a current density of 1 A cm^-3. The cycling durability and mechanical flexibility of the Ni/Fe battery were tested, which show good prospect for practical application. In summary, these merits make it possible for our Ni/Fe battery to have practical applications in next generation flexible energy storage devices.

All-Metal Phosphide Electrodes for High-Performance Quasi-Solid-State Fiber-Shaped Aqueous Rechargeable Ni-Fe Batteries

Aqueous secondary Ni-Fe batteries with superior energy density, cost-effectiveness, and outstanding safety contribute significantly toward the development of portable and wearable energy storage devices with high performance. However, the common electrode materials are nickel/iron or their oxides which have suffered from poor conductivity and cycle performance. As an ideal candidate to address these issues, metal phosphides may offer outstanding theoretical specific capacity, low conversion potential, and impressive redox. In this study, one novel type of high-performance flexible Ni-Fe battery with binder-free electrodes on conductive fiber substrates is successfully designed and fabricated. Carbon nanotube fibers with the direct grown hierarchical NiCoP nanosheet arrays and FeP nanowire arrays are fabricated first using hydrothermal synthesis and then the pursuant gas phosphating process. With the assistance of the PVA-KOH gel electrolyte, our fiber-shaped aqueous rechargeable battery (FARB) presents negligible capacity loss after bending 3000 times. Meanwhile, the assembled FARB has a significant capacity of 0.294 mA h/cm² under the current density of 2 mA/cm² and a high energy density of 235.6 μW h/cm².

Stabilizing Metallic Iron Nanoparticles by Conformal Graphitic Carbon Coating for High-Rate Anode in Ni-Fe Batteries

Nickel-iron (Ni-Fe) batteries are promising candidates for large-scale energy storage due to their high safety and low cost. However, their power density and cycling efficiency remain limited by the poor kinetics of the Fe anode. Herein, we report high-performance Fe anodes based on active Fe nanoparticles conformally coated with carbon shells, which were synthesized from low-cost precursors using a scalable process. Such core-shell structured C-Fe anodes offer high electrochemical activity and stability. Specifically, a high specific capacity of 208 mAh g^-1 at a current density of 1 A g^-1 (based on the total weight of Fe and C) and a capacity retention of 93% after 2000 cycles at 4 A g^-1 can be achieved. When coupled with a Ni cathode, such a full cell battery can deliver a high energy density of 101.0 Wh kg^-1 at power density of 0.81 kW kg^-1 and 51.6 Wh kg^-1 at 8.2 kW kg^-1 (based on the mass of the electrode materials), among the best energy and power performance among Ni-Fe batteries reported results. Thus, this work may provide an effective and scalable route toward high-performance anodes for high-power and long-life Ni-Fe batteries.

Interfacial Engineering Coupled Valence Tuning of MoO3 Cathode for High-Capacity and High-Rate Fiber-Shaped Zinc-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) have garnered the researchers' spotlight owing to its high safety, cost effectiveness, and high theoretical capacity of Zn anode. However, the availability of cathode materials for Zn ions storage is limited. With unique layered structure along the [010] direction, α-MoO₃ holds great promise as a cathode material for ZIBs, but its intrinsically poor conductivity severely restricts the capacity and rate capability. To circumvent this issue, an efficient surface engineering strategy is proposed to significantly improve the electric conductivity, Zn ion diffusion rate, and cycling stability of the MoO₃ cathode for ZIBs, thus drastically promoting its electrochemical properties. With the synergetic effect of Al₂ O₃ coating and phosphating process, the constructed Zn//P-MoO_{3- x} @Al₂ O₃ battery delivers impressive capacity of 257.7 mAh g^-1 at 1 A g^-1 and superior rate capability (57% capacity retention at 20 A g^-1 ), dramatically surpassing the pristine Zn//MoO₃ battery (115.8 mAh g^-1 ; 19.7%). More importantly, capitalized on polyvinyl alcohol gel electrolyte, an admirable capacity (19.2 mAh cm^-3 ) as well as favorable energy density (14.4 mWh cm^-3 ; 240 Wh kg^-1 ) are both achieved by the fiber-shaped quasi-solid-state ZIB. This work may be a great motivation for further research on molybdenum or other layered structure materials for high-performance ZIBs.

Noninterference Revealing of "Layered to Layered" Zinc Storage Mechanism of δ-MnO2 toward Neutral Zn-Mn Batteries with Superior Performance

MnO2 is one of the most studied cathodes for aqueous neutral zinc-ion batteries. However, the diverse reported crystal structures of MnO2 compared to δ-MnO2 inevitably suffer a structural phase transition from tunneled to layered Zn-buserite during the initial cycles, which is not as kinetically direct as the conventional intercalation electrochemistry in layered materials and thus poses great challenges to the performance and multifunctionality of devices. Here, a binder-free δ-MnO2 cathode is designed and a favorable "layered to layered" Zn2+ storage mechanism is revealed systematically using such a "noninterferencing" electrode platform in combination with ab initio calculation. A flexible quasi-solid-state Zn-Mn battery with an electrodeposited flexible Zn anode is further assembled, exhibiting high energy density (35.11 mWh cm-3; 432.05 Wh kg-1), high power density (676.92 mW cm-3; 8.33 kW kg-1), extremely low self-discharge rate, and ultralong stability up to 10 000 cycles. Even with a relatively high δ-MnO2 mass loading of 5 mg cm-2, significant energy and power densities are still achieved. The device also works well over a broad temperature range (0-40 °C) and can efficiently power different types of small electronics. This work provides an opportunity to develop high-performance multivalent-ion batteries via the design of a kinetically favorable host structure.

Incorporating Fe into Bismuthic Anode Systems: A Smart "Merits Combination/Complementation" Route to Build Better Ni-Bi Batteries

The advancement of Ni-Bi batteries has turned sluggish because of impenetrable barriers related to physicochemical instability of bismuthic species under thermal conditions. This directly makes Bi-based anodes impossible to hybridize with graphitic carbons for a longer-term cyclic lifespan. To break this constraint, we herein propose an effective strategy by incorporating Fe into bismuthic systems to form multielement anodes. The smart Bi/Fe merits combination/complementation can drastically promote the tolerable temperature of Bi-containing nanomaterials over 500 °C, enabling carbon encapsulation without altering their geometric properties and in the meantime endowing the anodes with inherited electrochemical superiorities. The as-built BiFeO₃@carbon anodes exhibit prominent electrode performances with excellent electrochemical activity (both Bi- and Fe-based components act as faradaic redox reaction sites), excellent rate capabilities, and impressive capacity retention (∼83.4% after 2000 cycles). We further unveil the anodic phase conversions of "BiFeO₃ → Bi₂O₃/Fe₂O₃" (via the transition state of Bi₂O₃₍₂₂₂₎) based on the real-time characterizations/post-analysis at distinct cyclic stages. The packed full cells exhibit max. energy/power densities of ∼90.72 W h kg^-1/∼1.3 kW kg^-1. Our study may offer a promising engineering route to promote the development of safe and applicable Ni-Bi batteries in near-future applications.