Carbon materials are generally preferred as anodes in supercapacitors; however, their low capacitance limits the attained energy density of supercapacitor devices with aqueous electrolytes. Here, we report a low-crystalline iron oxide hydroxide nanoparticle anode with comprehensive electrochemical performance at a wide potential window. The iron oxide hydroxide nanoparticles present capacitances of 1,066 and 716 F g−1 at mass loadings of 1.6 and 9.1 mg cm−2, respectively, a rate capability with 74.6% of capacitance retention at 30 A g−1, and cycling stability retaining 91% of capacitance after 10,000 cycles. The performance is attributed to a dominant capacitive charge-storage mechanism. An aqueous hybrid supercapacitor based on the iron oxide hydroxide anode shows stability during float voltage test for 450 h and an energy density of 104 Wh kg−1 at a power density of 1.27 kW kg−1. A packaged device delivers gravimetric and volumetric energy densities of 33.14 Wh kg−1 and 17.24 Wh l−1, respectively.

Electrocatalytic water splitting is one of the sustainable and promising strategies to generate hydrogen fuel but still remains a great challenge because of the sluggish anodic oxygen evolution reaction (OER). A very effective approach to dramatically decrease the input cell voltage of water electrolysis is to replace the anodic OER with hydrazine oxidation reaction (HzOR) due to its lower thermodynamic oxidation potential. Therefore, developing the low-cost and efficient HzOR catalysts, coupled with the cathodic hydrogen evolution reaction (HER) is tremendously important for energysaving electrolytic hydrogen production. Herein, a new-type copper-nickel nitride (Cu 1 Ni 2 -N) with rich Cu 4 N/Ni 3 N interface is rationally constructed on the carbon fiber cloth. The three-dimensional electrode exhibits extraordinary HER performance with an overpotential of 71.4 mV at 10 mA cm -2 in 1.0 M KOH, simultaneously delivering an ultralow potential of 0.5 mV at 10 mA cm -2 for HzOR in 1.0 M KOH/0.5 M hydrazine electrolyte. Moreover, the electrolytic cell utilizing the synthesized Cu 1 Ni 2 -N electrode as both the cathode and anode displays a cell voltage of 0.24 V at 10 mA cm -2 with an excellent stability over 75 h. The present work develops the promising copper-nickel-based nitride as a bifunctional electrocatalyst through hydrazine-assistance for energy-saving electrolytic hydrogen production.

Transition metal oxides have attracted much interest for their high energy density in lithium batteries. However, the fast capacity fading and the low power density still limit their practical implementation. In order to overcome these challenges, one-dimensional yolk-shell nanorods have been successfully constructed using manganese oxide as an example through a facile two-step sol-gel coating method. Dopamine and tetraethoxysilane are used as precursors to obtain uniform polymer coating and silica layer followed by converting into carbon shell and hollow space, respectively. As anode material for lithium batteries, the manganese oxide/carbon yolk-shell nanorod electrode has a reversible capacity of 660 mAh/g for initial cycle at 100 mA/g and exhibits excellent cyclability with a capacity of 634 mAh/g after 900 cycles at a current density of 500 mA/g. An enhanced capacity is observed during the long-term cycling process, which may be attributed to the structural integrity, the stability of solid electrolyte interphase layer, and the electrochemical actuation of the yolk-shell nanorod structure. The results demonstrate that the manganese oxide is well utilized with the one-dimensional yolk-shell structure, which represents an efficient way to realize excellent performance for practical applications.

Recently, layered transition-metal dichalcogenides (TMDs) have gained great attention for their analogous graphite structure and high theoretical capacity. However, it has suffered from rapid capacity fading. Herein, we present the crumpled reduced graphene oxide (RGO) decorated MoS2 nanoflowers on carbon fiber cloth. The three-dimensional framework of interconnected crumpled RGO and carbon fibers provides good electronic conductivity and facile strain release during electrochemical reaction, which is in favor of the cycling stability of MoS2. The crumpled RGO decorated MoS2 nanoflowers anode exhibits high specific capacity (1225 mAh/g) and excellent cycling performance (680 mAh/g after 250 cycles). Our results demonstrate that the three-dimensional crumpled RGO/MoS2 nanoflowers anode is one of the attractive anodes for lithium-ion batteries.

electric grids, as well as biocompatible technologies, has attracted tremendous attention and is still a big challenge in the energy field. [1-4] The electrochemical energy storage and conversion devices, such as rechargeable batteries, supercapacitors, fuel cells, and electrolyzers, have been extensively explored. It is well known that electrode materials, e.g., anodes, cathodes, and catalysts, are the heart components of these devices, which play a decisive role in determining performance. Mesoporous materials, which have pore sizes ranging from 2 to 50 nm defined by the International Union of Pure and Applied Chemistry, possess exceptional features, including high specific surface areas, large pore volumes, tunable pore sizes, and controllable geometries (Figure 1a-c). These features enable mesoporous materials as ideal candidates for energy conversion and storage because of the increased active reaction sites and enhanced transport efficiency of reactants. [3,5-7] Therefore, many precise manipulations and structural engineering strategies have been applied to construct advanced mesoporous electrodes with excellent electrochemical performance. Besides, the achieved electrodes with well-controlled mesoporous architectures could be used as platforms to study the fundamental research about the mass transport kinetics, charge transfer, and storage mechanism, as well as the interface electrochemical reactions behavior under the mesoporous nanoconfined space (Figure 1d-g). These fundamental studies are of great importance for further guiding the design of high-performance mesoporous electrodes for electrochemical energy storage and conversion. [6,8,9] In this Essay, we introduce the methods for synthesizing different types of mesoporous materials. Also, the key developments of applications of mesoporous materials in electrochemical energy conversion and storage devices are highlighted. The synthesis-structure-property of mesoporous materials and their applications in rechargeable batteries, supercapacitors, fuel cells, and electrolyzers have been detailed, providing creative insight and enlightening comments on the construction of high-performance mesoporous electrodes. Following these, we propose the research challenges and perspectives on mesoporous materials for the future development of energy conversion and storage devices. Developing high-performance electrode materials is an urgent requirement for next-generation energy conversion and storage systems. Due to the exceptional features, mesoporous materials have shown great potential to achieve high-performance electrodes with high energy/power density, long lifetime, increased interfacial reaction activity, and enhanced kinetics. In this Essay, applications of mesoporous materials are reviewed in electrochemical energy conversion and storage devices. The synthesis, structure, and properties of mesoporous materials and their performance in rechargeable batteries, supercapacitors, fuel cells, and electrolyzers are discussed, providing practical details and enligh...

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Iridium (Ir)-based electrocatalysts are widely explored as benchmarks for acidic oxygen evolution reactions (OERs). However, further enhancing their catalytic activity remains challenging due to the difficulty in identifying active species and unfavorable architectures. In this work, we synthesized ultrathin Ir-IrO x /C nanosheets with ordered interlayer space for enhanced OER by a nanoconfined self-assembly strategy, employing block copolymer formed stable end-merged lamellar micelles. The interlayer distance of the prepared Ir-IrO x /C nanosheets was well controlled at ∼20 nm and Ir-IrO x nanoparticles (∼2 nm) were uniformly distributed within the nanosheets. Importantly, the fabricated Ir-IrO x /C electrocatalysts display one of the lowest overpotential (η) of 198 mV at 10 mA cm −2 geo during OER in an acid medium, benefiting from their features of mixed-valence states, rich electrophilic oxygen species (O (II-δ)− ), and favorable mesostructured architectures. Both experimental and computational results reveal that the mixed valence and O (II-δ)− moieties of the 2D mesoporous Ir-IrO x /C catalysts with a shortened Ir−O (II-δ)− bond (1.91 Å) is the key active species for the enhancement of OER by balancing the adsorption free energy of oxygen-containing intermediates. This strategy thus opens an avenue for designing high performance 2D ordered mesoporous electrocatalysts through a nanoconfined selfassembly strategy for water oxidation and beyond.

kinetics in anodic electrode, that is, the four-electron coupled oxygen evolution reaction (OER). [1][2][3] At present, the benchmark OER catalysts are noble metalbased oxides such as IrO 2 and RuO 2 ; however, they are limited by scarcity and expensive cost. [4][5][6] Given this fact, the relatively inexpensive and performancepromising transition metal-based catalysts such as Fe/Co/Ni oxohydroxide and oxides are attracting increasing attention. [7][8][9][10][11][12] Ligand-modulation of Fe/Co/Ni-based metal-organic frameworks (MOFs) and hydroxides have demonstrated great potential in OER. [13][14][15][16][17] Through ligand modulation, the crystalline structure and mass/charge transfer behaviors of catalysts could be effectively modified, and enhanced OER performance could be achieved. For example, by a ligand-competition amorphization pathway, Yu et al. [18] reported a nanorod@nanosheet core-shell structured amorphous OER catalyst, consisting of a Fe-rich MOF core, a Co-rich MOF shell, and an amorphous Co(OH) 2 nanosheet outer layer. Taking advantage of the 3D amorphous architecture, the obtained OER catalyst demonstrates a small overpotential of 249 mV at 10 mA cm -2 . Hou et al. [19] reported the construction of N-doped carbon nanosheet networks with abundant active sites and enhanced charge transfer for OER using the complexes of ZIF-8 and layered double hydroxides as the precursors. Regardless of the research progress, understanding the intrinsic active sites of OER catalyst as well as the structure-performance correlation is still challenging.Herein, we report a 2-methylimidazole (MI) modulated cobalt-iron oxyhydroxide OER catalyst, (Fe,Co)OOH/MI, with low crystallinity and nanosheet structure. The low-crystalline nanosheet structure maximizes the exposure of active sites and facilitates the mass transfer process, while the MI modulation optimizes the electronic configuration of the catalyst. Specifically, the coordination of MI with (Fe,Co)OOH reduces the orbital overlap between Fe/Co 3d and O 2p, which weakens the adsorption to oxygen-containing intermediates and thus facilitates the unfavorable O 2 desorption. As expected, the (Fe,Co) OOH/MI demonstrates ultralow overpotentials of 230/290 mV at 10/100 mA cm -2 and affords more than 155-h durability with negligible decay in OER. Rationally designed catalystshold the key to address the sluggish kinetics of oxygen evolution reaction (OER). However, engineering the active sites of such catalysts still faces grand challenges. This study proposes a feasible ligand modulation strategy to boost the OER catalytic activity of cobalt-iron oxyhydroxide ((Fe,Co)OOH). The 2-methylimidazole (MI) ligand coordination on (Fe,Co)OOH reduces the orbital overlap between the Fe/Co 3d and O 2p, which weakens the adsorption to oxygen-containing intermediates and thus facilitates the unfavorable O 2 desorption. As a result, the MI ligand modulated (Fe,Co)OOH achieves an excellent OER performance with low overpotentials (230/290 mV at 10/100 mA cm -2 ) and excellent durability (...