In situ electrochemical synthesis of Pd aerogels as highly efficient anodic electrocatalysts for alkaline fuel cells.

Improving the utilization of noble metals is extremely urgent for fuel cell electrocatalysis, while three-dimensional hierarchical noble metal aerogels with abundant sites and channels are proposed to reinforce their electrocatalytic performances and decrease their amounts. Herein, novel Pd aerogels with tunable surface chemical states were prepared through a facile in situ electrochemical activation, starting with PdO x aerogels by the hydrolysis method. The hierarchical porous Pd aerogels showed unprecedented high activity towards the electrocatalytic oxidation of fuels including methanol (2.99 A mgPd -1), ethanol (8.81 A mgPd -1), and others in alkali, outperforming commercial catalysts (7.12- and 13.66-fold, corresponding to methanol and ethanol). Theoretical investigation unveiled the hybrid surface states with metallic and oxidized Pd species in Pd aerogels to regulate the adsorption of intermediates and facilitate the synergistic oxidation of adsorbed *CO, resulting in enhanced activity with the MOR as the model. Therefore, efficient Pd aerogels through the in situ electrochemical activation of PdO x aerogels were proposed and showed great potential for fuel cell anodic electrocatalysis.

Superelastic, Highly Conductive, Superhydrophobic, and Powerful Electromagnetic Shielding Hybrid Aerogels Built from Orthogonal Graphene and Boron Nitride Nanoribbons.

Three-dimensional (3D) elastic aerogels enable diverse applications but are usually restricted by their low thermal and electrical transfer efficiency. Here, we demonstrate a strategy for fabricating the highly thermally and electrically conductive aerogels using hybrid carbon/ceramic structural units made of hexagonal boron nitride nanoribbons (BNNRs) with in situ-grown orthogonally structured graphene (OSG). High-aspect-ratio BNNRs are first interconnected into a 3D elastic and thermally conductive skeleton, in which the horizontal graphene layers of OSG provide additional hyperchannels for electron and phonon conduction, and the vertical graphene sheets of OSG greatly improve surface roughness and charge polarization ability of the entire skeleton. The resulting OSG/BNNR hybrid aerogel exhibits very high thermal and electrical conductivity (up to 7.84 W m-1 K-1 and 340 S m-1, respectively) at a low density of 45.8 mg cm-3, which should prove to be vastly advantageous as compared to the reported carbonic and/or ceramic aerogels. Moreover, the hybrid aerogel possesses integrated properties of wide temperature-invariant superelasticity (from -196 to 600 °C), low-voltage-driven Joule heating (up to 42-134 °C at 1-4 V), strong hydrophobicity (contact angel of up to 156.1°), and powerful broadband electromagnetic interference (EMI) shielding effectiveness (reaching 70.9 dB at 2 mm thickness), all of which can maintain very well under repeated mechanical deformations and long-term immersion in strong acid or alkali solution. Using these extraordinary comprehensive properties, we prove the great potential of OSG/BNNR hybrid aerogel in wearable electronics for regulating body temperature, proofing water and pollution, removing ice, and protecting human health against EMI.

Ultraviolet-Cured Semi-Interpenetrating Network Polymer Electrolytes for High-Performance Quasi-Solid-State Lithium Metal Batteries.

Solid polymer electrolytes with relatively low ionic conductivity at room temperature and poor mechanical strength greatly restrict their practical applications. Herein, we design semi-interpenetrating network polymer (SNP) electrolyte composed of an ultraviolet-crosslinked polymer network (ethoxylated trimethylolpropane triacrylate), linear polymer chains (polyvinylidene fluoride-co-hexafluoropropylene) and lithium salt solution to satisfy the demand of high ionic conductivity, good mechanical flexibility, and electrochemical stability for lithium metal batteries. The semi-interpenetrating network has a pivotal effect in improving chain relaxation, facilitating the local segmental motion of polymer chains and reducing the polymer crystallinity. Thanks to these advantages, the SNP electrolyte shows a high ionic conductivity (1.12 mS cm-1 at 30 °C), wide electrochemical stability window (4.6 V vs. Li+ /Li), good bendability and shape versatility. The promoted ion transport combined with suppressed impedance growth during cycling contribute to good cell performance. The assembled quasi-solid-state lithium metal batteries (LiFePO4 /SNP/Li) exhibit good cycling stability and rate capability at room temperature.

High-Performance Multifunctional Carbon-Silicon Carbide Composites with Strengthened Reduced Graphene Oxide.

Materials with low density, exceptional thermal and corrosion resistance, and ultrahigh mechanical and electromagnetic interference (EMI) shielding performance are urgently demanded for aerospace and military industries. Efficient design of materials' components and microstructures is crucial yet remains highly challenging for achieving the above requirements. Herein, a strengthened reduced graphene oxide (SrGO)-reinforced multi-interfacial carbon-silicon carbide (C-SiC)n matrix (SrGO/(C-SiC)n) composite is reported, which is fabricated by depositing a carbon-strengthening layer into rGO foam followed by alternate filling of pyrocarbon (PyC) and silicon carbide (SiC) via a precursor infiltration pyrolysis (PIP) method. By increasing the number of alternate PIP sequences (n = 1, 3 and 12), the mechanical, electrical, and EMI shielding properties of SrGO/(C-SiC)n composites are significantly increased. The optimal composite exhibits excellent conductivity of 8.52 S·cm-1 and powerful average EMI shielding effectiveness (SE) of 70.2 dB over a broad bandwidth of 32 GHz, covering the entire X-, Ku-, K-, and Ka-bands. The excellent EMI SE benefits from the massive conduction loss in highly conductive SrGO skeletons and polarization relaxation of rich heterogeneous PyC/SiC interfaces. Our composite features low density down to 1.60 g·cm-3 and displays robust compressive properties (up to 163.8 MPa in strength), owing to the uniformly distributed heterogeneous interfaces capable of consuming great fracture energy upon loadings. Moreover, ultrahigh thermostructural stability (up to 2100 °C in Ar) and super corrosion resistance (no strength degradation after long-term acid and alkali immersion) are also discovered. These excellent comprehensive properties, along with ease of low-cost and scalable production, could potentially promote the practical applications of the SrGO/(C-SiC)n composite in the near future.

Solvent-free nanoalumina loaded nanocellulose aerogel for efficient oil and organic solvent adsorption.

HYPOTHESIS: Cellulose-based aerogel, due to its rich reserves, environmental friendliness and porous structure, is considered as a new type of adsorbents for treating oil and water pollution. However, the functionalization of cellulose aerogel is still required for the efficient increase of its adsorption performance in wide applications. The combination of nanomaterials could significantly improve the adsorption capability of nanocellulose aerogel. EXPERIMENTS: In this work, nanocomposite aerogels comprising of nanocellulose and nanoalumina (NC/Al2O3) are produced via a solvent-free method and the effect of weight ratios between nanocellulose and nanoalumina on the adsorption properties of NC/Al2O3 aerogels has been studied. FINDINGS: The results reveal that the NC/Al2O3 aerogel with a low density of 5.1 mg cm-3 could obtain the optimal pore microstructures and the highest oil and organic solvent adsorption capacities with the preparation condition under the nanocellulose/nanoalumina weight ratio of 1:0.25 and 0.4 wt% of nanocellulose in aqueous solution. The presence of nanoalumina facilitates the change of microstructure morphologies, the increase of BET specific surface area and the adsorption capacities of NC aerogel. Compared with pure NC aerogel (74.07 ± 1.67, 69.87 ± 1.01, 81.21 ± 3.20, 52.07 ± 1.70, 48.49 ± 1.01, 75.45 ± 3.58 and 87.03 ± 0.46 g g-1 for thiophene, anhydrous ethanol, ethyl acetate, cyclohexane, sesame oil, acetone and dichloromethane, respectively), the NC/Al2O3 aerogel manifests an outstanding adsorption capacity (108.07 ± 0.37, 89.91 ± 4.83, 93.93 ± 3.81, 71.13 ± 2.48, 64.83 ± 2.25, 85.19 ± 3.87 and 117.65 ± 5.68 g g-1, accordingly). By considering the desirable performance features and the convenient fabrication approach, this nanocellulose nanocomposite aerogel might be a feasible alternative for oily waste water recovery and conservation of environment.

Silver-Quantum-Dot-Modified MoO3 and MnO2 Paper-Like Freestanding Films for Flexible Solid-State Asymmetric Supercapacitors.

Free-standing paper-like thin-film electrodes have great potential to boost next-generation power sources with highly flexible, ultrathin, and lightweight requirements. In this work, silver-quantum-dot- (2-5 nm) modified transition metal oxide (including MoO3 and MnO2 ) paper-like electrodes are developed for energy storage applications. Benefitting from the ohmic contact at the interfaces between silver quantum dots and MoO3 nanobelts (or MnO2 nanowires) and the binder-free nature and 0D/1D/2D nanostructured 3D network of the fabricated electrodes, substantial improvements on the electrical conductivity, efficient ionic diffusion, and areal capacitances of the hybrid nanostructure electrodes are observed. With this proposed strategy, the constructed asymmetric supercapacitors, with Ag quantum dots/MoO3 "paper" as anode, Ag quantum dots/MnO2 "paper" as cathode, and neutral Na2 SO4 /polyvinyl alcohol hydrogel as electrolyte, exhibit significantly enhanced energy and power densities in comparison with those of the supercapacitors without modification of Ag quantum dots on electrodes; present excellent cycling stability at different current densities and good flexibility under various bending states; offer possibilities as high-performance power sources with low cost, high safety, and environmental friendly properties.

Flexible Sub-Micro Carbon Fiber@CNTs as Anodes for Potassium-Ion Batteries.

Potassium-ion batteries (KIBs) with potential cost benefits are a promising alternative to lithium-ion batteries (LIBs). However, because of the large radius of K+, current anode materials usually undergo large volumetric expansion and structural collapse during the charge-discharge process. Self-supporting carbon nanotubes encapsulated in sub-micro carbon fiber (SMCF@CNTs) are utilized as the KIB anode in this study. The SMCF@CNT anode exhibits high specific capacity, good rate performance, and cycling stability. The SMCF@CNT electrode has specific capacities of 236 mAh g-1 at 0.1 C and 108 mAh g-1 at 5 C and maintains over 193 mAh g-1 after 300 cycles at 1 C. Furthermore, a combined capacitive and diffusion-controlled K+ storage mechanism is proposed on the basis of the investigation using in situ Raman and quantitative analyses. By coupling the SMCF@CNT anode with the K0.3MnO2 cathode, a pouch cell with good flexibility delivers a capacity of 74.0 mAh g-1 at 20 mA g-1. This work is expected to promote the application of KIBs in wearable electronics.

Self-Templating Synthesis of Cobalt Hexacyanoferrate Hollow Structures with Superior Performance for Na-Ion Hybrid Supercapacitors.

Prussian blue (PB) and its analogues (PBA), especially with hollow structures, have attracted growing attention from the researchers of energy storage field. Herein, we have developed a facile self-templating method to synthesize hollow-structured cobalt hexacyanoferrate (CoHCF) with controllable morphologies by using water-soluble precursors as templates. The method is versatile and can be extended to synthesize various PB/PBA hollow structures with tunable composition and morphology. Profiting from the unique hollow structure, the CoHCF hollow prisms manifest exceptional electrochemical performance in the Na2SO4 aqueous electrolyte, including a high specific capacitance (284 F g-1 at 1 A g-1), a high rate capability, and an excellent cycling stability (92% retention after 5000 cycles). A hybrid supercapacitor device assembled with the CoHCF hollow prisms and activated carbon shows a high specific density of 47 W h kg-1 at a specific power of 1000 W kg-1 and stable cycling performance.

Carbon Nanotube-Multilayered Graphene Edge Plane Core-Shell Hybrid Foams for Ultrahigh-Performance Electromagnetic-Interference Shielding.

Materials with an ultralow density and ultrahigh electromagnetic-interference (EMI)-shielding performance are highly desirable in fields of aerospace, portable electronics, and so on. Theoretical work predicts that 3D carbon nanotube (CNT)/graphene hybrids are one of the most promising lightweight EMI shielding materials, owing to their unique nanostructures and extraordinary electronic properties. Herein, for the first time, a lightweight, flexible, and conductive CNT-multilayered graphene edge plane (MLGEP) core-shell hybrid foam is fabricated using chemical vapor deposition. MLGEPs are seamlessly grown on the CNTs, and the hybrid foam exhibits excellent EMI shielding effectiveness which exceeds 38.4 or 47.5 dB in X-band at 1.6 mm, while the density is merely 0.0058 or 0.0089 g cm-3 , respectively, which far surpasses the best values of reported carbon-based composite materials. The grafted MLGEPs on CNTs can obviously enhance the penetration losses of microwaves in foams, leading to a greatly improved EMI shielding performance. In addition, the CNT-MLGEP hybrids also exhibit a great potential as nano-reinforcements for fabricating high-strength polymer-based composites. The results provide an alternative approach to fully explore the potentials of CNT and graphene, for developing advanced multifunctional materials.

Silicide Coating Fabricated by HAPC/SAPS Combination to Protect Niobium Alloy from Oxidation.

A combined silicide coating, including inner NbSi2 layer and outer MoSi2 layer, was fabricated through a two-step method. The NbSi2 was deposited on niobium alloy by halide activated pack cementation (HAPC) in the first step. Then, supersonic atmospheric plasma spray (SAPS) was applied to obtain the outer MoSi2 layer, forming a combined silicide coating. Results show that the combined coating possessed a compact structure. The phase constitution of the combined coating prepared by HAPC and SAPS was NbSi2 and MoSi2, respectively. The adhesion strength of the combined coating increased nearly two times than that for single sprayed coating, attributing to the rougher surface of the HAPC-bond layer whose roughness increased about three times than that of the grit-blast substrate. After exposure at 1200 °C in air, the mass increasing rate for single HAPC-silicide coating was 3.5 mg/cm(2) because of the pest oxidation of niobium alloy, whereas the combined coating displayed better oxidation resistance with a mass gain of only 1.2 mg/cm(2). Even more, the combined coating could significantly improve the antioxidation ability of niobium based alloy at 1500 °C. The good oxidation resistance of the combined silicide coating was attributed to the integrity of the combined coating and the continuous SiO2 protective scale provided by the oxidation of MoSi2.

Density functional theory study on the interactions of L-cysteine with graphene: adsorption stability and magnetism.

Understanding the interactions between graphene and biomolecules is of fundamental relevance to the area of nanobiotechnology. Herein, we take l-cysteine as the probe biomolecule and investigate its adsorption on pristine graphene and B-, N-, Al-, Ni-, Ga-, Pd-doped graphene using density functional theory calculations. Three kinds of upright adsorption configurations, via unprotonated functional groups (-SH, -NH2, -COOH), are considered. The calculations reveal pristine graphene physically adsorbs l-cysteine. N-doped graphene shows physisorption towards the S-end and N-end l-cysteine, and chemisorption towards the O-end radical. Strong chemisorption, with site-specific preference, occurs on Al-, Ni-, Ga- and Pd-doped graphene, accompanied by severe structural changes. Spin polarization with an unusual mirror symmetry on Ni- and Pd-doped graphene is induced by chemisorption of unprotonated l-cysteine, except for O-end adsorption on Pd-doped graphene. The magnetization arises mainly from spin polarization of the C 2pz orbital, with a minor magnetism located on Ni or Pd. The influence of van der Waals forces is also evaluated. A thorough analysis of the adsorption stability and magnetism of these systems would be beneficial to facilitate applications in graphene-based biosensing, biomolecule immobilization, magnetic bio-separation and other fields in bionanotechnology.

Large-scale production of graphene by microwave synthesis and rapid cooling.

Graphene was prepared via carbonization of microwave synthesized metal phthalocyanine, followed by a rapid cooling process. The morphology and structure of the obtained graphene were controlled by the coolants.