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.

Super-strong and tough poly(vinyl alcohol)/poly(acrylic acid) hydrogels based on hydrogen bonding are prepared by the strategy of immersing and cold-drawing.

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Fabrication of hydrogels with unique microstructures and better mechanical properties through the self-assembly of commercially available synthetic polymers and small molecules is of great scientific and practical importance. A type of physical hydrogels is prepared by the self-assembly of polyvinyl alcohol (PVA) and tannic acid (TA) in aqueous solution with a low PVA–TA concentration (0.5–6.0 wt %) at room temperature. With the increase of the PVA–TA concentration, the water content of the hydrogels increases, and the content of TA in the hydrogels decreases from 23.1 to 6.4%. The driving force for the self-assembly is proven to be the hydrogen bonding between PVA and TA, which also induces the crystallization of PVA chains. The self-assembled PVA–TA hydrogels have diverse morphologies that change from microspheres to oriented porous structures with the increase of the PVA–TA concentration, and these structures are all composed of nanosized particles, fibers, and/or sheets. Most of the self-assembled PVA–TA hydrogels show good mechanical properties. The highest tensile strength and elastic modulus of the PVA–TA hydrogel prepared with 1.0 wt % PVA–TA concentration are about 84 and 30 kPa, respectively. This self-assembly method would lead to the fabrication of more hydrogels with unique microstructures and properties for practical applications.

Shape memory hydrogels (SMHs) have a wide range of potential practical applications. However, the mechanically weak and soft nature of most SMHs strongly impedes their applications. Here, we report a novel kind of thermal-responsive SMH with high tensile strength and high elastic moduli. Organogels are first prepared by the copolymerization of a hydrophilic monomer N-vinylpyrrolidone (NVP) and a hydrophobic monomer acryloxy acetophenone (AAP) in N, N'-dimethylformamide (DMF) solutions, and then, poly(vinylpyrrolidone- co-acryloxy acetophenone) [poly(NVP- co-AAP)] hydrogels are obtained by solvent exchange with water. Because of the strong and reversible hydrophobic association and π-π stacking of acetophenone groups, the poly(NVP- co-AAP) hydrogels exhibit tensile strengths up to 8.41 ± 0.83 MPa and Young's moduli up to 94.2 ± 1.3 MPa, which are more than 1 or 3 orders of magnitude higher than those of the organogels, respectively. The poly(NVP- co-AAP) hydrogels exhibit good shape memory behaviors, with a complete fixation ratio and a recovery ratio of 74-89%, as well as very fast shape-fixing and recovering rates (in seconds). These rigid and strong hydrogels are demonstrated to be an ideal shape memory material for surgical fixation devices to wrap around and support various shapes of limbs.