A new type of multistimuli‐responsive hydrogels cross‐linked by metal ions and biopolymers is reported. By mixing the biopolymer chitosan (CS) with a variety of metal ions at the appropriate pH ...values, we obtained a series of transparent and stable hydrogels within a few seconds through supramolecular complexation. In particular, the CS–Ag hydrogel was chosen as the model and the gelation mechanism was revealed by various measurements. It was found that the facile association of Ag+ ions with amino and hydroxy groups in CS chains promoted rapid gel‐network formation. Interestingly, the CS–Ag hydrogel exhibits sharp phase transitions in response to multiple external stimuli, including pH value, chemical redox reactions, cations, anions, and neutral species. Furthermore, this soft matter showed a remarkable moldability to form shape‐persistent, free‐standing objects by a fast in situ gelation procedure.
Turning to jelly: A series of metal–biopolymer hydrogels is obtained by ultrafast supramolecular complexation. The hydrogels are easily prepared, have high water content, and are stable at room temperature. The multistimuli‐responsive Ag‐based hydrogel can be molded to form shape‐persistent, free‐standing objects.
It is a challenge to prepare organic electrodes for sodium-ion batteries with long cycle life and high capacity. The highly reactive radical intermediates generated during the sodiation/desodiation ...process could be a critical issue because of undesired side reactions. Here we present durable electrodes with a stabilized α-C radical intermediate. Through the resonance effect as well as steric effects, the excessive reactivity of the unpaired electron is successfully suppressed, thus developing an electrode with stable cycling for over 2,000 cycles with 96.8% capacity retention. In addition, the α-radical demonstrates reversible transformation between three states: C=C; α-C·radical; and α-C
anion. Such transformation provides additional Na
storage equal to more than 0.83 Na
insertion per α-C radical for the electrodes. The strategy of intermediate radical stabilization could be enlightening in the design of organic electrodes with enhanced cycling life and energy storage capability.
Active and highly stable electrocatalysts for oxygen evolution reaction (OER) in acidic media are currently in high demand as a cleaner alternative to the combustion of fossil fuels. Herein, we ...report a Co-doped nanorod-like RuO2 electrocatalyst with an abundance of oxygen vacancies achieved through the facile, one-step annealing of a Ru-exchanged ZIF-67 derivative. The compound exhibits ultra-high OER performance in acidic media, with a low overpotential of 169 mV at 10 mA cm−2 while maintaining excellent activity, even when exposed to a 50-h galvanostatic stability test at a constant current of 10 mA cm−2. The dramatic enhancement in OER performance is mainly attributed to the abundance of oxygen vacancies and modulated electronic structure of the Co-doped RuO2 that rely on a vacancy-related lattice oxygen oxidation mechanism (LOM) rather than adsorbate evolution reaction mechanism (AEM), as revealed and supported by experimental characterizations as well as density functional theory (DFT) calculations.
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•A Co-doped RuO2 electrocatalyst with an abundance of oxygen vacancies was synthesized•The compound exhibits ultra-high OER performance in acidic media•The oxygen vacancies contribute to the high OER performance
Catalysis; Electrochemical Energy Production; Nanomaterials
A thin and compact mixed matrix membrane containing CAU-1-NH2 and the poly(methyl methacrylate) polymer has been originally synthesized. The as-prepared membrane exhibits high permeability of H2 and ...excellent H2/CO2 selectivity.
Novel three-dimensional （3D） concentration-gradient Ni-Co hydroxide nanostructures （3DCGNC） have been directly grown on nickel foam by a facile stepwise electrochemical deposition method and ...intensively investigated as binder- and conductor-free electrode for supercapacitors. Based on a three- electrode electrochemical characterization technique, the obtained 3DCGNC electrodes demonstrated a high specific capacitance of 1,760 F·g^-1 and a remarkable rate capability whereby more than 62.5% capacitance was retained when the current density was raised from 1 to 100 A·g^-1. More importantly, asymmetric supercapacitors were assembled by using the obtained 3DCGNC as the cathode and Ketjenblack as a conventional activated carbon anode. The fabricated asymmetric supercapacitors exhibited very promising electrochemical performances with an excellent combination of high energy density of 103.0 Wh·kg^-1 at a power density of 3.0 kW·kg^-1, and excellent rate capability-energy densities of about 70.4 and 26.0 Wh·kg^-1 were achieved when the average power densities were increased to 26.2 and 133.4 kW·kg^-1, respectively. Moreover, an extremely stable cycling life with only 2.7% capacitance loss after 20,000 cycles at a current density of 5 A·g^-1 was achieved, which compares very well with the traditional doublelayer supercapacitors.
A porous hollow high-entropy metal organic framework (MOF-74) consisting of Mn, Fe, Co, Ni, Cu and Zn is prepared through one-pot hydrothermal method. Then, a high-entropy nanocomposite is prepared ...and evaluated as electrocatalyst for oxygen reduction reaction (ORR). The optimal nanocomposite comprising of metal-particle (Mn, Fe, Co, Cu), metal-alloy (Cu0·18Ni0.91, Co0·52Cu0.48) and metal-oxide (ZnO) exhibites very promising ORR performance due to the unique synergistic effect between multi-component high-entropy feature and hollow nanostructure. The approach of high-entropy nanocomposite is enlightening in developing high performance electrocatalysts.
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•Hollow high-entropy metal organic frameworks consisiting of Mn, Fe, Co, Ni, Cu and Zn.•Porous high-entropy nanocomposite comprising of metals, alloys, metal oxides.•Synergistic effect of high-entropy and nanoporous hollow features leads to outstanding electrocatalytic oxygen reduction reaction activities.
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► Fine-structured barium phosphate (BP) nano-flake has been studied as adsorbent. ► High adsorption capacity of methyl blue (MB) onto BP was about 1500mg/g. ► The adsorption for MB ...was highly selective. ► Ionic and hydrogen bonds existed between BP and MB by XPS and calculation analysis.
We report the synthesis of barium phosphate (BP) nano-flake and its adsorption behavior to methyl blue (MB) in aqueous solution. The as-obtained BP nano-flake revealed pure rhombohedral crystal structure. The adsorption capacity of MB onto BP reached 1500mgg−1. The adsorption equilibrium results fitted well with the Freundlich isotherm model. The adsorption process took less than 30min to reach equilibrium. The adsorption kinetics was elucidated by the pseudo-second-order kinetic equation. It followed 2-stage and 3-stage intra-particle diffusion models for the low and high concentration of dye solutions, respectively. The adsorption of MB using the BP nano-flake was highly selective, compared with the adsorption of other dyes. The interactions between MB and BP were mainly the ionic interaction and hydrogen bonds, which were confirmed by the X-ray photoelectron spectroscopic results and the density functional theory calculations. The BP nano-flake revealed less than 5% decrease in adsorption amount when it was recycled and reused five times. The present work shows that the BP nano-flake is promising for practical applications in MB removal from aqueous solutions.
Catalysts of oxygen reduction reaction (ORR) play key roles in renewable energy technologies such as metal-air batteries and fuel cells. Despite tremendous efforts, highly active catalysts with low ...cost remain elusive. This work used metal-organic frameworks to synthesize non-precious bimetallic carbon nanocomposites as efficient ORR catalysts. Although carbon-based Cu and Ni are good candidates, the hybrid nanocomposites take advantage of both metals to improve catalytic activity. The resulting molar ratio of Cu/Ni in the nanocomposites can be finely controlled by tuning the recipe of the precursors. Nanocomposites with a series of molar ratios were produced, and they exhibited much better ORR catalytic performance than their monometallic counterparts in terms of limited current density, onset potential and half-wave potential. In addition, their extraordinary stability in alkaline is superior to that of commercially-available Pt-based materials, which adds to the appeal of the bimetallic carbon nanocomposites as ORR catalysts. Their improved performance can be attributed to the synergetic effects of Cu and Ni, and the enhancement of the carbon matrix.
This paper presents the first detailed comparisons between experiments and direct numerical simulations (DNS) of inertial particle clustering in nearly isotropic ‘box turbulence’. The experimental ...system consists of a box 38cm in each dimension with fans in the eight corners that sustain nearly isotropic turbulence in the centre of the box. We inject hollow glass spheres with a mean diameter of 6 μm and measure the locations of several hundred particles in a 1 cm3 volume in the centre of the box using three-dimensional digital holographic particle imaging. We observe particle concentration fluctuations that result from inertial clustering (sometimes called ‘preferential concentration’). The radial distribution function (RDF), a statistical measure of clustering, has been calculated from the particle position field. We select this measure because of its relevance to the collision kernel for particles. DNS of the equivalent system, with nearly perfect parameter overlap, have also been performed. We observe good agreement between the RDF predictions of the DNS and the experimental observations, despite some challenges in the interpretation of the experiments. The results provide important guidance on ways to improve the measurement.
It is a great challenge to prepare non-noble metal electrocatalysts toward hydrogen evolution reaction (HER) with large current density. Synergistic electronic and morphological structures of the ...catalyst have been considered as an effective method to improve the catalytic performance, due to the enhanced intrinsic activity and enlarged accessible active sites. Herein, we present novel ternary Co
1−
x
V
x
P nano-needle arrays with modulated electronic and morphological structures as an electrocatalyst for highly efficient HER in alkaline solution. The NF@Co
1−
x
V
x
P catalyst shows a remarkable catalytic ability with low overpotentials of 46 and 226 mV at current densities of 10 and 400 mA cm
−2
, respectively, as well as a small Tafel slope and superior stability. Combining the experimental and computational study, the excellent catalytic performance was attributed to the improved physical and chemical properties (conductivity and surface activity), large active surface area, and fast reaction kinetics. Furthermore, the assembled Co-V based electrolyzer (NF@Co
1−
x
V
x
-HNNs(+)||NF@Co
1−
x
V
x
P(−)) delivers small full-cell voltages of 1.58, 1.75, and 1.92 V at 10, 100, and 300 mA cm
−2
, respectively. Our findings provide a systematic understanding on the V-incorporation strategy to promote highly efficient ternary electrocatalysts
via
synergistic control of morphology and electronic structures.
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