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Hierarchical NiCo2O4@NiCo2O4 core/shell nanoflake arrays on nickel foam for high-performance supercapacitors are fabricated by a two-step solution-based method which involves in hydrothermal process and chemical bath deposition. Compared with the bare NiCo2O4 nanoflake arrays, the core/shell electrode displays better pseudocapacitive behaviors in 2 M KOH, which exhibits high areal specific capacitances of 1.55 F cm(-2) at 2 mA cm(-2) and 1.16 F cm(-2) at 40 mA cm(-2) before activation as well as excellent cycling stability. The specific capacitance can achieve a maximum of 2.20 F cm(-2) at a current density of 5 mA cm(-2), which can still retain 2.17 F cm(-2) (98.6% retention) after 4000 cycles. The enhanced pseudocapacitive performances are mainly attributed to its unique core/shell structure, which provides fast ion and electron transfer, a large number of active sites, and good strain accommodation.

Porous materials have been thriving as promising candidates for vast applications in current electrochemical energy storage field. [1][2][3] The rational design of porous architectures with hierarchical and interconnected pore networks is always strongly considered by scientific community. [4][5][6][7] In parallel with the microporous (pore size ≤ 2 nm) and mesoporous (2 nm ≤ pore size ≤ 50 nm) materials, macroporous (50 nm ≤ pore size) materials emerge and hold tremendous potentials due to their significant advantages with interconnected frameworks offering improved structural stability, as well as large channels for accelerated mass mobilization and accessibility advantageous over micro/mesoporous materials. [8] In addition, many electrochemical energy storage applications require an open cellular structure with a reasonable combination of hierarchical pore size and distribution, of which the macropores work together with mesopores and micropores to accelerate transport mass (e.g., chemicals and electrolyte), thus highlighting the necessity and importance of macropores in a porous hierarchy. [9] Porous macrocellular carbon, one member of macroporous material family, is of particularly great interest due to their excellent chemical, mechanical, and thermal stability coupled with good conductivity and high surface area. Thus, various carbonaceous porous materials (e.g., 3D rGO, [10] porous graphene, [11][12][13] carbon nanorods, [14] carbon nanotube networks, [15] microporous carbon, [16] hierarchical porous carbon, [17] biomass derived carbon, [18][19][20][21] and their hybrids) [22][23][24] are endowed with a wide range of applications in lithium ion batteries, [25] sodium ion batteries, [26] and supercapacitors. [27] Diverse techniques have been developed to fabricate macroporous carbon materials including template, [27] suspension, [28] microfluidics, [29] membrane/microchannel emulsification, [9] and seeded emulsion polymerization, [30] etc. However, such methodologies are tedious, requiring multiple synthetic steps, caustic chemical treatments, and long curing times. Therefore, it is with great interest to develop facile approaches for large-scale construction of macroporous materials.Puffing process has been extensively accepted to produce 3D edible and degradable foam from starch-based materials (e.g., (2 of 8)rice, corn, wheat, potato). [31] As a typical puffing method, the instantaneous puffing (IP) involving compression and instantaneous release processes is widely accepted for popcorn fabrication. In general, the grains are first compressed in a heated and sealed container. Then, the starch-containing feedstocks are puffed/expanded in a flash by instantaneous release of clamping force of the sealed container at a high temperature of ≈200-300 °C and a large pressure of 0.5-1.5 MPa. The bulk starch-containing feedstocks are instantaneously transformed into expanded 3D porous macrocellular materials with volume and surface area increased by dozens of times through the facile IP process. This technolog...

Elemental sulfur cathodes for lithium/sulfur cells are still in the stage of intensive research due to their unsatisfactory capacity retention and cyclability. The undesired capacity degradation upon cycling originates from gradual diffusion of lithium polysulfides out of the cathode region. To prevent losses of certain intermediate soluble species and extend lifespan of cells, the effective encapsulation of sulfur plays a critical role. Here we report an applicable way, by using thin-layered nickel-based hydroxide as a feasible and effective encapsulation material. In addition to being a durable physical barrier, such hydroxide thin films can irreversibly react with lithium to generate protective layers that combine good ionic permeability and abundant functional polar/hydrophilic groups, leading to drastic improvements in cell behaviours (almost 100% coulombic efficiency and negligible capacity decay within total 500 cycles). Our present encapsulation strategy and understanding of hydroxide working mechanisms may advance progress on the development of lithium/sulfur cells for practical use.

A new and generic strategy to construct interwoven carbon nanotube (CNT) branches on various metal oxide nanostructure arrays (exemplified by V2 O3 nanoflakes, Co3 O4 nanowires, Co3 O4 -CoTiO3 composite nanotubes, and ZnO microrods), in order to enhance their electrochemical performance, is demonstrated for the first time. In the second part, the V2 O3 /CNTs core/branch composite arrays as the host for Na(+) storage are investigated in detail. This V2 O3 /CNTs hybrid electrode achieves a reversible charge storage capacity of 612 mAh g(-1) at 0.1 A g(-1) and outstanding high-rate cycling stability (a capacity retention of 100% after 6000 cycles at 2 A g(-1) , and 70% after 10 000 cycles at 10 A g(-1) ). Kinetics analysis reveals that the Na(+) storage is a pseudocapacitive dominating process and the CNTs improve the levels of pseudocapacitive energy by providing a conductive network.

A Co(3)O(4) monolayer hollow-sphere array with mesoporous walls exhibits high pseudocapacitances of 358 F g(-1) at 2 A g(-1) and 305 F g(-1) at 40 A g(-1), as well as excellent cycling stability for application as pseudocapacitors.

We report the preparation of a nickel-foam-supported graphene sheet/porous NiO hybrid film by the combination of electrophoretic deposition and chemical-bath deposition. The obtained graphene-sheet film of about 19 layers was used as the nanoscale substrate for the formation of a highly porous NiO film made up of interconnected NiO flakes with a thickness of 10-20 nm. The graphene sheet/porous NiO hybrid film exhibits excellent pseudocapacitive behavior with pseudocapacitances of 400 and 324 F g(-1) at 2 and 40 A g(-1), respectively, which is higher than those of the porous NiO film (279 and 188 F g(-1) at 2 and 40 A g(-1)). The enhancement of the pseudocapacitive properties is due to reinforcement of the electrochemical activity of the graphene-sheet film.

Fast, high-yield, and controllable synthesis of functional hydroxide and oxide nanomaterials on conductive substrates is highly desirable for the energy generation and storage applications. For the same purpose, three-dimensional hierarchical porous nanostructures are being regarded advantageous. In this work, we report the fabrication of porous metal hydroxide nanosheets on a preformed nanowires scaffold using the fast and well-controllable electrodeposition method. Co-(OH) 2 and Mn(OH) 2 nanosheets are electrochemically deposited on the Co 3 O 4 core nanowires to form core/shell arrays. Such oxide/hydroxide core/shell nanoarrays can be realized on various conductive substrates. The Co 3 O 4 /Co(OH) 2 core/shell nanowire arrays are evaluated as a supercapacitor cathode material that exhibits high specific capacitances of 1095 F/g at 1 A/g and 812 F/g at 40 A/g, respectively. The mesoporous homogeneous Co 3 O 4 core/shell nanowire arrays, obtained by annealing the Co 3 O 4 /Co(OH) 2 sample, are applied as the anode material for lithium ion batteries. A high capacity of 1323 mAh/g at 0.5 C and excellent cycling stability are demonstrated. Our results show that electrodeposition is a versatile technique for fabrication of nanometal oxides on 3-D templates for electrochemical energy applications.