Intertwined Nanocarbon and Manganese Oxide Hybrid Foam for High‐Energy Supercapacitors

Rapid charging and discharging supercapacitors are promising alternative energy storage systems for applications such as portable electronics and electric vehicles. Integration of pseudocapacitive metal oxides with single‐structured materials has received a lot of attention recently due to their superior electrochemical performance. In order to realize high energy‐density supercapacitors, a simple and scalable method is developed to fabricate a graphene/MWNT/MnO₂ nanowire (GMM) hybrid nanostructured foam, via a two‐step process. The 3D few‐layer graphene/MWNT (GM) architecture is grown on foamed metal foils (nickel foam) via ambient pressure chemical vapor deposition. Hydrothermally synthesized α‐MnO₂ nanowires are conformally coated onto the GM foam by a simple bath deposition. The as‐prepared hierarchical GMM foam yields a monographical graphene foam conformally covered with an intertwined, densely packed CNT/MnO₂ nanowire nanocomposite network. Symmetrical electrochemical capacitors (ECs) based on GMM foam electrodes show an extended operational voltage window of 1.6 V in aqueous electrolyte. A superior energy density of 391.7 Wh kg^?1 is obtained for the supercapacitor based on the GMM foam, which is much higher than ECs based on GM foam only (39.72 Wh kg^?1). A high specific capacitance (1108.79 F g^?1) and power density (799.84 kW kg^?1) are also achieved. Moreover, the great capacitance retention (97.94%) after 13 000 charge–discharge cycles and high current handability demonstrate the high stability of the electrodes of the supercapacitor. These excellent performances enable the innovative 3D hierarchical GMM foam to serve as EC electrodes, resulting in energy‐storage devices with high stability and power density in neutral aqueous electrolyte.     

Strongly Coupled Pyridine‐V2O5·nH2O Nanowires with Intercalation Pseudocapacitance and Stabilized Layer for High Energy Sodium Ion Capacitors

Developing pseudocapacitive cathodes for sodium ion capacitors (SICs) is very significant for enhancing energy density of SICs. Vanadium oxides cathodes with pseudocapacitive behavior are able to offer high capacity. However, the capacity fading caused by the irreversible collapse of layer structure remains a major issue. Herein, based on the Acid–Base Proton theory, a strongly coupled layered pyridine‐V₂O₅·nH₂O nanowires cathode is reported for highly efficient sodium ion storage. By density functional theory calculations, in situ X‐ray diffraction, and ex situ Fourier‐transform infrared spectroscopy, a strong interaction between protonated pyridine and V?O group is confirmed and stable during cycling. The pyridine‐V₂O₅·nH₂O nanowires deliver long‐term cyclability (over 3000 cycles), large pseudocapacitive behavior (78% capacitive contribution at 1 mV s^?1) and outstanding rate capability. The assembled pyridine‐V₂O₅·nH₂O//graphitic mesocarbon microbead SIC delivers high energy density of ≈96 Wh kg^?1 (at 59 W kg^?1) and power density of 14 kW kg^?1 (at 37.5 Wh kg^?1). The present work highlights the strategy of realizing strong interaction in the interlayer of V₂O₅·nH₂O to enhance the electrochemical performance of vanadium oxides cathodes. The strategy could be extended for improving the electrochemical performance of other layered materials.     

Hierarchical 3D All‐Carbon Composite Structure Modified with N‐Doped Graphene Quantum Dots for High‐Performance Flexible Supercapacitors

Flexible supercapacitors have shown enormous potential for portable electronic devices. Herein, hierarchical 3D all‐carbon electrode materials are prepared by assembling N‐doped graphene quantum dots (N‐GQDs) on carbonized MOF materials (cZIF‐8) interweaved with carbon nanotubes (CNTs) for flexible all‐solid‐state supercapacitors. In this ternary electrode, cZIF‐8 provides a large accessible surface area, CNTs act as the electrical conductive network, and N‐GQDs serve as highly pseudocapactive materials. Due to the synergistic effect and hierarchical assembly of these components, N‐GQD@cZIF‐8/CNT electrodes exhibit a high specific capacitance of 540 F g^?1 at 0.5 A g^?1 in a 1 m H₂SO₄ electrolyte and excellent cycle stability with 90.9% capacity retention over 8000 cycles. The assembled supercapacitor possesses an energy density of 18.75 Wh kg^?1 with a power density of 108.7 W kg^?1. Meanwhile, three supercapacitors connected in series can power light‐emitting diodes for 20 min. All‐solid‐state N‐GQD@cZIF‐8/CNT flexible supercapacitor exhibits an energy density of 14 Wh kg^?1 with a power density of 89.3 W kg^?1, while the capacitance retention after 5000 cycles reaches 82%. This work provides an effective way to construct novel electrode materials with high energy storage density as well as good cycling performance and power density for high‐performance energy storage devices via the rational design.     

Fast Supercapacitors Based on Graphene‐Bridged V2O3/VOx Core–Shell Nanostructure Electrodes with a Power Density of 1 MW kg−1

Transition metal oxides (TMOs), with their very large pseudocapacitance effect, hold promise for next generation high‐energy‐density electrochemical supercapacitors (ECs). However, the typical high resistivity of TMOs restricts the reported ECs to work at a low charge–discharge (C–D) rate of 0.1–1 V s⁻¹. Here, a novel vanadium oxides core/shell nanostructure‐based electrode to overcome the resistivity challenge of TMOs for rapid pseudocapacitive EC design is reported. Quasi‐metallic V₂O₃ nanocores are dispersed on graphene sheets for electrical connection of the whole structure, while a naturally formed amorphous VO₂ and V₂O₅ (called as VO_x here) thin shell around V₂O₃ nanocore acts as the active pseudocapacitive material. With such a graphene‐bridged V₂O₃/VO_x core–shell composite as electrode material, ECs with a C–D rate as high as 50 V s⁻¹ is demonstrated. This high rate was attributed to the largely enhanced conductivity of this unique structure and a possibly facile redox mechanism. Such an EC can provide 1000 kW kg⁻¹ power density at an energy density of 10 Wh kg⁻¹. At the critical 45° phase angle, these ECs have a measured frequency of 114 Hz. All these indicate the graphene‐bridged V₂O₃/VO_x core–shell structure is promising for fast EC development.     

A High‐Performance Lithium‐Ion Capacitor Based on 2D Nanosheet Materials

Lithium‐ion capacitors (LICs) are promising electrical energy storage systems for mid‐to‐large‐scale applications due to the high energy and large power output without sacrificing long cycle stability. However, due to the different energy storage mechanisms between anode and cathode, the energy densities of LICs often degrade noticeably at high power density, because of the sluggish kinetics limitation at the battery‐type anode side. Herein, a high‐performance LIC by well‐defined ZnMn₂O₄‐graphene hybrid nanosheets anode and N‐doped carbon nanosheets cathode is presented. The 2D nanomaterials offer high specific surface areas in favor of a fast ion transport and storage with shortened ion diffusion length, enabling fast charge and discharge. The fabricated LIC delivers a high specific energy of 202.8 Wh kg^?1 at specific power of 180 W kg^?1, and the specific energy remains 98 Wh kg^?1 even when the specific power achieves as high as 21 kW kg^?1.     

Highly Efficient Sodium Storage in Iron Oxide Nanotube Arrays Enabled by Built‐In Electric Field

High‐power sodium–ion batteries capable of charging and discharging rapidly and durably are eagerly demanded to replace current lithium–ion batteries. However, poor activity and instable cycling of common sodium anode materials represent a huge barrier for practical deployment. A smart design of ordered nanotube arrays of iron oxide (Fe₂O₃) is presented as efficient sodium anode, simply enabled by surface sulfurization. The resulted heterostructure of oxide and sulfide spontaneously develops a built‐in electric field, which reduces the activation energy and accelerates charge transport significantly. Benefiting from the synergy of ordered architecture and built‐in electric field, such arrays exhibit a large reversible capacity, a superior rate capability, and a high retention of 91% up to 200 cycles at a high rate of 5 A g^?1, outperforming most reported iron oxide electrodes. Furthermore, full cells based on the Fe₂O₃ array anode and the Na_0.67(Mn_0.67Ni_0.23Mg_0.1)O₂ cathode deliver a specific energy of 142 Wh kg^?1 at a power density of 330 W kg^?1 (based on both active electrodes), demonstrating a great potential in practical application. This material design may open a new door in engineering efficient anode based on earth‐abundant materials.     

Pseudocapacitance of TiO2−x/CNT Anodes for High‐Performance Quasi‐Solid‐State Li‐Ion and Na‐Ion Capacitors

It is challenging for flexible solid‐state hybrid capacitors to achieve high‐energy‐high‐power densities in both Li‐ion and Na‐ion systems, and the kinetics discrepancy between the sluggish faradaic anode and the rapid capacitive cathode is the most critical issue needs to be addressed. To improve Li‐ion/Na‐ion diffusion kinetics, flexible oxygen‐deficient TiO_2?x/CNT composite film with ultrafast electron/ion transport network is constructed as self‐supported and light‐weight anode for a quasi‐solid‐state hybrid capacitor. It is found that the designed porous yolk–shell structure endows large surface area and provides short diffusion length, the oxygen‐deficient composite film can improve electrical conductivity, and enhance ion diffusion kinetic by introducing intercalation pseudocapacitance, therefore resulting in advance electrochemical properties. It exhibits high capacity, excellent rate performance, and long cycle life when utilized as self‐supported anodes for Li‐ion and Na‐ion batteries. When assembled with activated carbon/carbon nanotube (AC/CNT) flexible cathode, using ion conducting gel polymer as the electrolyte, high energy densities of 104 and 109 Wh kg^?1 are achieved at 250 W kg^?1 in quasi‐solid‐state Li‐ion and Na‐ion capacitors (LICs and SICs), respectively. Still, energy densities of 32 and 36 Wh kg^?1 can be maintained at high power densities of 5000 W kg^?1 in LICs and SICs.     

Beyond Activated Carbon: Graphite‐Cathode‐Derived Li‐Ion Pseudocapacitors with High Energy and High Power Densities

Supercapacitors have aroused considerable attention due to their high power capability, which enables charge storage/output in minutes or even seconds. However, to achieve a high energy density in a supercapacitor has been a long‐standing challenge. Here, graphite is reported as a high‐energy alternative to the frequently used activated carbon (AC) cathode for supercapacitor application due to its unique Faradaic pseudocapacitive anion intercalation behavior. The graphite cathode manifests both higher gravimetric and volumetric energy density (498 Wh kg^?1 and 431.2 Wh l^?1) than an AC cathode (234 Wh kg^?1 and 83.5 Wh l^?1) with peak power densities of 43.6 kW kg^?1 and 37.75 kW l^?1. A new type of Li‐ion pseudocapacitor (LIpC) is thus proposed and demonstrated with graphite as cathode and prelithiated graphite or Li₄Ti₅O₁₂ (LTO) as anode. The resultant graphite–graphite LIpCs deliver high energy densities of 167–233 Wh kg^?1 at power densities of 0.22–21.0 kW kg^?1 (based on active mass in both electrodes), much higher than 20–146 Wh kg^?1 of AC‐derived Li‐ion capacitors and 23–67 Wh kg^?1 of state‐of‐the‐art metal oxide pseudocapacitors. Excellent rate capability and cycling stability are further demonstrated for LTO‐graphite LIpCs.     

Caging Nb2O5 Nanowires in PECVD‐Derived Graphene Capsules toward Bendable Sodium‐Ion Hybrid Supercapacitors

Sodium‐ion hybrid supercapacitors (Na‐HSCs) by virtue of synergizing the merits of batteries and supercapacitors have attracted considerable attention for high‐energy and high‐power energy‐storage applications. Orthorhombic Nb₂O₅ (T‐Nb₂O₅) has recently been recognized as a promising anode material for Na‐HSCs due to its typical pseudocapacitive feature, but it suffers from intrinsically low electrical conductivity. Reasonably high electrochemical performance of T‐Nb₂O₅‐based electrodes could merely be gained to date when sufficient carbon content was introduced. In addition, flexible Na‐HSC devices have scarcely been demonstrated by far. Herein, an in situ encapsulation strategy is devised to directly grow ultrathin graphene shells over T‐Nb₂O₅ nanowires (denoted as Gr‐Nb₂O₅ composites) by plasma‐enhanced chemical vapor deposition, targeting a highly conductive anode material for Na‐HSCs. The few‐layered graphene capsules with ample topological defects would enable facile electron and Na⁺ ion transport, guaranteeing rapid pseudocapacitive processes at the Nb₂O₅/electrolyte interface. The Na‐HSC full‐cell comprising a Gr‐Nb₂O₅ anode and an activated carbon cathode delivers high energy/power densities (112.9 Wh kg^?1/80.1 W kg^?1 and 62.2 Wh kg^?1/5330 W kg^?1), outperforming those of recently reported Na‐HSC counterparts. Proof‐of‐concept Na‐HSC devices with favorable mechanical robustness manifest stable electrochemical performances under different bending conditions and after various bending–release cycles.     

Pine‐Needle‐Like Cu–Co Skeleton Composited with Li4Ti5O12 Forming Core–Branch Arrays for High‐Rate Lithium Ion Storage

High‐performance of lithium‐ion batteries (LIBs) rely largely on the scrupulous design of nanoarchitectures and smart hybridization of bespoke active materials. In this work, the pine‐needle‐like Cu–Co skeleton is reported to support highly active Li₄Ti₅O₁₂ (LTO) forming Cu–Co/LTO core–branch arrays via a united hydrothermal‐atomic layer deposition (ALD) method. ALD‐formed LTO layer is uniformly anchored on the pine‐needle‐like heterostructured Cu–Co backbone, which consists of branched Co nanowires (diameters in 20 nm) and Cu nanowires (250–300 nm) core. The designed Cu–Co/LTO core–branch arrays show combined advantages of large porosity, high electrical conductivity, and good adhesion. Due to the unique positive features, the Cu–Co/LTO electrodes are demonstrated with enhanced electrochemical performance including excellent high‐rate capacity (155 mAh g^?1 at 20 C) and noticeable long‐term cycles (144 mAh g^?1 at 20 C after 3000 cycles). Additionally, the full cell assembled with activated carbon positive electrode and Cu–Co/LTO negative electrode exhibits high power/energy densities (41.6 Wh kg^?1 at 7.5 kW kg^?1). The design protocol combining binder‐free characteristics and array configuration opens a new door for construction of advanced electrodes for application in high‐rate electrochemical energy storage.     

Peapod‐like Li3VO4/N‐Doped Carbon Nanowires with Pseudocapacitive Properties as Advanced Materials for High‐Energy Lithium‐Ion Capacitors

Lithium ion capacitors are new energy storage devices combining the complementary features of both electric double‐layer capacitors and lithium ion batteries. A key limitation to this technology is the kinetic imbalance between the Faradaic insertion electrode and capacitive electrode. Here, we demonstrate that the Li₃VO₄ with low Li‐ion insertion voltage and fast kinetics can be favorably used for lithium ion capacitors. N‐doped carbon‐encapsulated Li₃VO₄ nanowires are synthesized through a morphology‐inheritance route, displaying a low insertion voltage between 0.2 and 1.0 V, a high reversible capacity of ≈400 mAh g^?1 at 0.1 A g^?1, excellent rate capability, and long‐term cycling stability. Benefiting from the small nanoparticles, low energy diffusion barrier and highly localized charge‐transfer, the Li₃VO₄/N‐doped carbon nanowires exhibit a high‐rate pseudocapacitive behavior. A lithium ion capacitor device based on these Li₃VO₄/N‐doped carbon nanowires delivers a high energy density of 136.4 Wh kg^?1 at a power density of 532 W kg^?1, revealing the potential for application in high‐performance and long life energy storage devices.     

Water‐Lubricated Intercalation in V2O5·nH2O for High‐Capacity and High‐Rate Aqueous Rechargeable Zinc Batteries

Low‐cost, environment‐friendly aqueous Zn batteries have great potential for large‐scale energy storage, but the intercalation of zinc ions in the cathode materials is challenging and complex. Herein, the critical role of structural H₂O on Zn²⁺ intercalation into bilayer V₂O₅·nH₂O is demonstrated. The results suggest that the H₂O‐solvated Zn²⁺ possesses largely reduced effective charge and thus reduced electrostatic interactions with the V₂O₅ framework, effectively promoting its diffusion. Benefited from the “lubricating” effect, the aqueous Zn battery shows a specific energy of ≈144 Wh kg^?1 at 0.3 A g^?1. Meanwhile, it can maintain an energy density of 90 Wh kg^?1 at a high power density of 6.4 kW kg^?1 (based on the cathode and 200% Zn anode), making it a promising candidate for high‐performance, low‐cost, safe, and environment‐friendly energy‐storage devices.     

A Metal‐Free,Free‐Standing,Macroporous Graphene@g‐C3N4 Composite Air Electrode for High‐Energy Lithium Oxygen Batteries

The nonaqueous lithium oxygen battery is a promising candidate as a next‐generation energy storage system because of its potentially high energy density (up to 2–3 kW kg^?1), exceeding that of any other existing energy storage system for storing sustainable and clean energy to reduce greenhouse gas emissions and the consumption of nonrenewable fossil fuels. To achieve high energy density, long cycling stability, and low cost, the air electrode structure and the electrocatalysts play important roles. Here, a metal‐free, free‐standing macroporous graphene@graphitic carbon nitride (g‐C₃N₄) composite air cathode is first reported, in which the g‐C₃N₄ nanosheets can act as efficient electrocatalysts, and the macroporous graphene nanosheets can provide space for Li₂O₂ to deposit and also promote the electron transfer. The electrochemical results on the graphene@g‐C₃N₄ composite air electrode show a 0.48 V lower charging plateau and a 0.13 V higher discharging plateau than those of pure graphene air electrode, with a discharge capacity of nearly 17300 mA h g^?1 _(composite). Excellent cycling performance, with terminal voltage higher than 2.4 V after 105 cycles at 1000 mA h g^?1 _(composite) capacity, can also be achieved. Therefore, this hybrid material is a promising candidate for use as a high energy, long‐cycle‐life, and low‐cost cathode material for lithium oxygen batteries.     

Co@Co3O4 Core–Shell Three‐Dimensional Nano‐Network for High‐Performance Electrochemical Energy Storage

An alternative routine is presented by constructing a novel architecture, conductive metal/transition oxide (Co@Co₃O₄) core–shell three‐dimensional nano‐network (3DN) by surface oxidating Co 3DN in situ, for high‐performance electrochemical capacitors. It is found that the Co@Co₃O₄ core–shell 3DN consists of petal‐like nanosheets with thickness of <10 nm interconnected forming a 3D porous nanostructure, which preserves the original morphology of Co 3DN well. X‐ray photoelectron spectroscopy by polishing the specimen layer by layer reveals that the Co@Co₃O₄ nano‐network is core–shell‐like structure. In the application of electrochemical capacitors, the electrodes exhibit a high specific capacitance of 1049 F g^?1 at scan rate of 2 mV/s with capacitance retention of ～52.05% (546 F g^?1 at scan rate of 100 mV) and relative high areal mass density of 850 F g^?1 at areal mass of 3.52 mg/cm². It is believed that the good electrochemical behaviors mainly originate from its extremely high specific surface area and underneath core‐Co “conductive network”. The high specific surface area enables more electroactive sites for efficient Faradaic redox reactions and thus enhances ion and electron diffusion. The underneath core‐Co “conductive network” enables an ultrafast electron transport.     

A Dual‐Stimuli‐Responsive Sodium‐Bromine Battery with Ultrahigh Energy Density

Stimuli‐responsive energy storage devices have emerged for the fast‐growing popularity of intelligent electronics. However, all previously reported stimuli‐responsive energy storage devices have rather low energy densities (<250 Wh kg^–1) and single stimuli‐response, which seriously limit their application scopes in intelligent electronics. Herein, a dual‐stimuli‐responsive sodium‐bromine (Na//Br₂) battery featuring ultrahigh energy density, electrochromic effect, and fast thermal response is demonstrated. Remarkably, the fabricated Na//Br₂ battery exhibits a large operating voltage of 3.3 V and an energy density up to 760 Wh kg^?1, which outperforms those for the state‐of‐the‐art stimuli‐responsive electrochemical energy storage devices. This work offers a promising approach for designing multi‐stimuli‐responsive and high‐energy rechargeable batteries without sacrificing the electrochemical performance.     

Mesopore‐Induced Ultrafast Na+‐Storage in T‐Nb2O5/Carbon Nanofiber Films toward Flexible High‐Power Na‐Ion Capacitors

Hybrid Na‐ion capacitors (NICs) are receiving considerable interest because they combine the merits of both batteries and supercapacitors and because of the low‐cost of sodium resources. However, further large‐scale deployment of NICs is impeded by the sluggish diffusion of Na⁺ in the anode. To achieve rapid redox kinetics, herein the controlled fabrication of mesoporous orthorhombic‐Nb₂O₅ (T‐Nb₂O₅)/carbon nanofiber (CNF) networks is demonstrated via in situ SiO₂‐etching. The as‐obtained mesoporous T‐Nb₂O₅ (m‐Nb₂O₅)/CNF membranes are mechanically flexible without using any additives, binders, or current collectors. The in situ formed mesopores can efficiently increase Na⁺‐storage performances of the m‐Nb₂O₅/CNF electrode, such as excellent rate capability (up to 150 C) and outstanding cyclability (94% retention after 10 000 cycles at 100 C). A flexible NIC device based on the m‐Nb₂O₅/CNF anode and the graphene framework (GF)/mesoporous carbon nanofiber (mCNF) cathode, is further constructed, and delivers an ultrahigh power density of 60 kW kg^?1 at 55 Wh kg^?1 (based on the total weight of m‐Nb₂O₅/CNF and GF/mCNF). More importantly, owing to the free‐standing flexible electrode configuration, the m‐Nb₂O₅/CNF//GF/mCNF NIC exhibits high volumetric energy and power densities (11.2 mWh cm^?3, 5.4 W cm^?3) based on the full device, which holds great promise in a wide variety of flexible electronics.     

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 Al₂O₃ coating and phosphating process, the constructed Zn//P‐MoO_3?x@Al₂O₃ 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.     

Phosphorus Regulated Cobalt Oxide@Nitrogen‐Doped Carbon Nanowires for Flexible Quasi‐Solid‐State Supercapacitors

Battery‐type materials are promising candidates for achieving high specific capacity for supercapacitors. However, their slow reaction kinetics hinders the improvement in electrochemical performance. Herein, a hybrid structure of P‐doped Co₃O₄ (P‐Co₃O₄) ultrafine nanoparticles in situ encapsulated into P, N co‐doped carbon (P, N‐C) nanowires by a pyrolysis–oxidation–phosphorization of 1D metal–organic frameworks derived from Co‐layered double hydroxide as self‐template and reactant is reported. This hybrid structure prevents active material agglomeration and maintains a 1D oriented arrangement, which exhibits a large accessible surface area and hierarchically porous feature, enabling sufficient permeation and transfer of electrolyte ions. Theoretical calculations demonstrate that the P dopants in P‐Co₃O₄@P, N‐C could reduce the adsorption energy of OH^? and regulate the electrical properties. Accordingly, the P‐Co₃O₄@P, N‐C delivers a high specific capacity of 669 mC cm^?2 at 1 mA cm^?2 and an ultralong cycle life with only 4.8% loss over 5000 cycles at 30 mA cm^?2. During the fabrication of P‐Co₃O₄@P, N‐C, Co@P, N‐C is simultaneously developed, which can be integrated with P‐Co₃O₄@P, N‐C for the assembly of asymmetric supercapacitors. These devices achieve a high energy density of 47.6 W h kg^?1 at 750 W kg^?1 and impressive flexibility, exhibiting a great potential in practical applications.     

Self‐Sacrificial Template‐Directed Vapor‐Phase Growth of MOF Assemblies and Surface Vulcanization for Efficient Water Splitting

Direct use of metal–organic frameworks (MOFs) with robust pore structures, large surface areas, and high density of coordinatively unsaturated metal sites as electrochemical active materials is highly desirable (rather than using as templates and/or precursors for high‐temperature calcination), but this is practically hindered by the poor conductivity and low accessibility of active sites in the bulk form. Herein, a universal vapor‐phase method is reported to grow well‐aligned MOFs on conductive carbon cloth (CC) by using metal hydroxyl fluorides with diverse morphologies as self‐sacrificial templates. Specifically, by further partially on‐site generating active Co₃S₄ species from Co ions in the echinops‐like Co‐based MOF (EC‐MOF) through a controlled vulcanization approach, the resulting Co₃S₄/EC‐MOF hybrid exhibits much enhanced electrocatalytic performance toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), with overpotentials of 84 and 226 mV required to reach a current density of 10 mA cm^?2, respectively. Density functional theory (DFT) calculations and experimental results reveal that the electron transfer between Co₃S₄ species and EC‐MOF can decrease the electron density of the Co d‐orbital, resulting in more electrocatalytically optimized adsorption properties for Co. This study will open up a new avenue for designing highly ordered MOF‐based surface active materials for various electrochemical energy applications.     

Novel MOF‐Derived Co@N‐C Bifunctional Catalysts for Highly Efficient Zn–Air Batteries and Water Splitting

Metal–organic frameworks (MOFs) and MOF‐derived materials have recently attracted considerable interest as alternatives to noble‐metal electrocatalysts. Herein, the rational design and synthesis of a new class of Co@N‐C materials (C‐MOF‐C2‐T) from a pair of enantiotopic chiral 3D MOFs by pyrolysis at temperature T is reported. The newly developed C‐MOF‐C2‐900 with a unique 3D hierarchical rodlike structure, consisting of homogeneously distributed cobalt nanoparticles encapsulated by partially graphitized N‐doped carbon rings along the rod length, exhibits higher electrocatalytic activities for oxygen reduction and oxygen evolution reactions (ORR and OER) than that of commercial Pt/C and RuO₂, respectively. Primary Zn–air batteries based on C‐MOF‐900 for the oxygen reduction reaction (ORR) operated at a discharge potential of 1.30 V with a specific capacity of 741 mA h g_Zn^–1 under 10 mA cm^–2. Rechargeable Zn–air batteries based on C‐MOF‐C2‐900 as an ORR and OER bifunctional catalyst exhibit initial charge and discharge potentials at 1.81 and 1.28 V (2 mA cm^–2), along with an excellent cycling stability with no increase in polarization even after 120 h – outperform their counterparts based on noble‐metal‐based air electrodes. The resultant rechargeable Zn–air batteries are used to efficiently power electrochemical water‐splitting systems, demonstrating promising potential as integrated green energy systems for practical applications.