Xu-Ming Xie

A self-healable and highly stretchable supercapacitor based on a dual crosslinked polyelectrolyte

Superior self-healability and stretchability are critical elements for the practical wide-scale adoption of personalized electronics such as portable and wearable energy storage devices. However, the low healing efficiency of self-healable supercapacitors and the small strain of stretchable supercapacitors are fundamentally limited by conventional polyvinyl alcohol-based acidic electrolytes, which are intrinsically neither self-healable nor highly stretchable. Here we report an electrolyte comprising polyacrylic acid dual crosslinked by hydrogen bonding and vinyl hybrid silica nanoparticles, which displays all superior functions and provides a solution to the intrinsic self-healability and high stretchability problems of a supercapacitor. Supercapacitors with this electrolyte are non-autonomic self-healable, retaining the capacitance completely even after 20 cycles of breaking/healing. These supercapacitors are stretched up to 600% strain with enhanced performance using a designed facile electrode fabrication procedure.

Self-healable, super tough graphene oxide–poly(acrylic acid) nanocomposite hydrogels facilitated by dual cross-linking effects through dynamic ionic interactions

Here we propose a facile, one-pot in situ free radical polymerization strategy to prepare self-healable, super tough graphene oxide (GO)-poly(acrylic acid) (PAA) nanocomposite hydrogels by using Fe3+ ions as a cross-linker. The 3-dimensional network structure of the GO-PAA nanocomposite hydrogels is facilitated by dual cross-linking effects through dynamic ionic interactions: (i) the first cross-linking points are Fe3+ ions creating ionic cross-linking among PAA chains; (ii) the second cross-linking points are GO nanosheets linking PAA chains through Fe3+ coordination. When the GO-PAA nanocomposite hydrogels are under stretching conditions, the ionic interactions among PAA chains can dynamically break and recombine to dissipate energy, while the GO nanosheets coordinated to the PAA chains maintain the configuration of the hydrogels and work as stress transfer centers transferring the stress to the polymer matrix. In this regard, the GO-PAA nanocomposite hydrogels exhibit superior toughness (tensile strength = 777 kPa, work of extension = 11.9 MJ m-3) and stretchability (elongation at break = 2980%). Furthermore, after being treated at 45 °C for 48 h, the cut-off GO-PAA nanocomposite hydrogels exhibit good self-healing properties (tensile strength = 495 kPa, elongation at break = 2470%). The self-healable, super tough GO-PAA nanocomposite hydrogels lay a basis for developing advanced soft materials holding potential applications in modern biomedical engineering and technology.

An Intrinsically Stretchable and Compressible Supercapacitor Containing a Polyacrylamide Hydrogel Electrolyte

Stretchability and compressibility of supercapacitors is an essential element of modern electronics, such as flexible, wearable devices. Widely used polyvinyl alcohol-based electrolytes are neither very stretchable nor compressible, which fundamentally limits the realization of supercapacitors with high stretchability and compressibility. A new electrolyte that is intrinsically super-stretchable and compressible is presented. Vinyl hybrid silica nanoparticle cross-linkers were introduced into polyacrylamide hydrogel backbones to promote dynamic cross-linking of the polymer networks. These cross-linkers serve as stress buffers to dissipate energy when strain is applied, providing a solution to the intrinsically low stretchability and compressibility shortcomings of conventional supercapacitors. The newly developed supercapacitor and electrolyte can be stretched up to an unprecedented 1000u2009% strain with enhanced performance, and compressed to 50u2009% strain with good retention of the initial performance.

Delicate ternary heterostructures achieved by hierarchical co-assembly of Ag and Fe3O4 nanoparticles on MoS2 nanosheets: morphological and compositional synergy in reversible lithium storage

Nanostructured transition metal oxides and dichalcogenides have recently emerged as promising anode candidates for lithium-ion batteries due to their extraordinarily high theoretical capacities. Unfortunately, these nanomaterials still face two problems that are detrimental to their ultimate electrochemical performances. First, the morphological deficiency, imposed by their strong tendency to aggregate, inevitably causes a frustrating loss in reversible capacities. Second, the compositional deficiency, resulting from their inherently low conductivity, further hastens the electrolyte degradation leading to awful cyclability. Herein we propose a facile strategy for the hierarchical co-assembly of Ag and Fe3O4 nanoparticles (NPs) on MoS2 nanosheets, aiming to address the morphological and compositional deficiencies simultaneously. The three building blocks, together, act as an appealing trio: (1) the large, elastic and flexible MoS2 nanosheets serve as an ideal substrate to prevent NP aggregation and accommodate the strains during repeated lithation/delithation; (2) the small Fe3O4 NPs contribute superior capacities and rate capabilities by ensuring short Li+ ion diffusion pathways; (3) the highly conductive Ag NPs allow for efficient charge transport. As such, prominent morphological and compositional synergy is emphasized by superior reversible capacities and rate capabilities, ranking our Ag/Fe3O4–MoS2 ternary heterostructures as high-performance anode materials.

Highly stretchable and super tough nanocomposite physical hydrogels facilitated by the coupling of intermolecular hydrogen bonds and analogous chemical crosslinking of nanoparticles

Highly stretchable and super tough nanocomposite physical hydrogels (NCP gels) were fabricated by a facile and one-pot process. NCP gels show superior mechanical properties with tensile strength of 73 kPa-313 kPa and elongation at break of 1210-3420%. This is due to the effective strengthening mechanism: under stretching, the intermolecular hydrogen bonds can dynamically break and recombine to dissipate energy and homogenize the gel network. In addition, vinyl hybrid silica nanoparticles (VSNPs) can work as stress transfer centres to transfer stress to the grafted polymer chains.

Constructing Novel Si@SnO2 Core–Shell Heterostructures by Facile Self-Assembly of SnO2 Nanowires on Silicon Hollow Nanospheres for Large, Reversible Lithium Storage

Developing an industrially viable silicon anode, featured by the highest theoretical capacity (4200 mA h g(-1)) among common electrode materials, is still a huge challenge because of its large volume expansion during repeated lithiation-delithiation as well as low intrinsic conductivity. Here, we expect to address these inherent deficiencies simultaneously with an interesting hybridization design. A facile self-assembly approach is proposed to decorate silicon hollow nanospheres with SnO2 nanowires. The two building blocks, hand in hand, play a wonderful duet by bridging their appealing functionalities in a complementary way: (1) The silicon hollow nanospheres, in addition to the major role as a superior capacity contributor, also act as a host material (core) to partially accommodate the volume expansion, thus alleviating the capacity fading by providing abundant hollow interiors, void spaces, and surface areas. (2) The SnO2 nanowires serve as a conductive coating (shell) to enable efficient electron transport due to a relatively high conductivity, thereby improving the cyclability of silicon. Compared to other conductive dopants, the SnO2 nanowires with a high theoretical capacity (790 mA h g(-1)) can contribute outstanding electrochemical reaction kinetics, further adding value to the ultimate electrochemical performances. The resulting novel Si@SnO2 core-shell heterostructures exhibit remarkable synergy in large, reversible lithium storage, delivering a reversible capacity as high as 1869 mA h g(-1)@500 mA g(-1) after 100 charging-discharging cycles.

Multi-dimensionally ordered, multi-functionally integrated r-GO@TiO2(B)@Mn3O4 yolk–membrane–shell superstructures for ultrafast lithium storage

TiO2(B) is an attractive new anode candidate for lithium-ion batteries (LIBs) due to its unique and highly desirable properties, including high structural integrity, long cycle life, and low cost. However, despite these merits, its inherent slow lithium and electron transport kinetics hinder its practical application to LIBs. Here, we propose a novel, simple route towards multi-dimensionally ordered, multi-functionally integrated reduced graphene oxide (r-GO)@TiO2(B)@Mn3O4 yolk–membrane–shell superstructures in which r-GO nanosheets, TiO2(B) nanosheets, and Mn3O4 nanoparticles are hierarchically organized to achieve remarkable synergistic interactions. This hybridization design is fundamentally bilateral in nature, aiming to overcome the conductivity and capacity deficiencies of TiO2(B) simultaneously. The resulting r-GO@TiO2(B)@Mn3O4 yolk–membrane–shell superstructures have great potential as advanced anode materials for ultrafast lithium storage, delivering a strikingly high reversible capacity of 662 mA·h·g−1 at 500 mA·g−1 after 500 charge–discharge cycles.

Robust and self-healable nanocomposite physical hydrogel facilitated by the synergy of ternary crosslinking points in a single network

Acrylamide (AM) and a small amount of stearyl methacrylate (C18) hydrophobic monomer copolymerize to graft on the surface of vinyl hybrid silica nanoparticles (VSNPs), forming nanobrush gelators, thereby constructing ternarily crosslinked nanocomposite physical hydrogels (TC-NCP gels). The TC-NCP gel is composed of a single network ternarily crosslinked by hydrogen bonds and hydrophobic interactions among the grafting polymer chains as physical cross-linking points and thus the polymer grafted VSNPs as analogous covalent crosslinking points. Under stretching, the physical crosslinking points successively break to gradually dissipate energy and then recombine to homogenize the network. During the stretching process, the polymer chains grafted VSNPs can homogenize the stress distribution as transferring centers. The synergy of the ternary crosslinking points leads the TC-NCP gels to dissipate more energy and redistribute the stress more effectively when compared with hydrogels dually crosslinked by both hydrogen bonds and VSNPs as analogous covalent crosslinking points (without hydrophobic interactions) and by both hydrogen bonds and hydrophobic interactions (without VSNPs). As a result, the TC-NCP gels demonstrate remarkably improved mechanical properties, including tensile strength of 256 kPa, stretch ratio at break of 28.23 and toughness of 1.92 MJ m-3 at a water content of 90%. Pure shear test shows that the TC-NCP gel is able to resist notch propagation by micro-crack development from the notch tip to the whole gel network and has a high tearing energy of 1.21 × 104 J m-2. The dynamic nature of the network endows the TC-NCP gels with excellent self-healing ability. The results evidently indicate that constructing a single gel network with hierarchical crosslinking points is a versatile method to fabricate robust hydrogels.

Facile and Green Production of Impurity-Free Aqueous Solutions of WS2 Nanosheets by Direct Exfoliation in Water.

To obtain 2D materials with large quantity, low cost, and little pollution, liquid-phase exfoliation of their bulk form in water is a particularly fascinating concept. However, the current strategies for water-borne exfoliation exclusively employ stabilizers, such as surfactants, polymers, or inorganic salts, to minimize the extremely high surface energy of these nanosheets and stabilize them by steric repulsion. It is worth noting, however, that the remaining impurities inevitably bring about adverse effects to the ultimate performances of 2D materials. Here, a facile and green route to large-scale production of impurity-free aqueous solutions of WS2 nanosheets is reported by direct exfoliation in water. Crucial parameters such as initial concentration, sonication time, centrifugation speed, and centrifugation time are systematically evaluated to screen out an optimized condition for scaling up. Statistics based on morphological characterization prove that substantial fraction (66%) of the obtained WS2 nanosheets are one to five layers. X-ray diffraction and Raman characterizations reveal a high quality with few, if any, structural distortions. The water-borne exfoliation route opens up new opportunities for easy, clean processing of WS2 -based film devices that may shine in the fields of, e.g., energy storage and functional nanocomposites owing to their excellent electrochemical, mechanical, and thermal properties.

Investigation of Hydrolysis in Poly(ethylene terephthalate) by FTIR-ATR

The hydrothermal aging of poly(ethylene terephthalate) (PET) was investigated at 70–95 °C. A new method to investigate the hydrolysis degree of PET by Fourier transform infrared spectroscopy (FTIR) was proposed. The spectra during the hydrothermal aging were measured using attenuated total reflection accessory (ATR). Peak resolving of carbonyl regions was performed, and the ratio of two groups of bands representing carboxylic acids and esters respectively were calculated to show the hydrolysis degree of ester groups in PET. The acid/ester ratio shows exactly the same trend as the average chain scission number per unit mass at various temperatures and thus can be used as a parameter to characterize the hydrolysis and random chain scission of PET. This method related to the hydrolysis mechanism directly, is simple, fast and convenient compared to the traditional methods such as viscometry, end-group titration and size exclusion chromatography (SEC). It may also be useful in hydrolysis characterization of other polyesters.