Kewei Shu

Intrinsically stretchable supercapacitors composed of polypyrrole electrodes and highly stretchable gel electrolyte

There has been an emerging interest in stretchable power sources compatible with flexible/wearable electronics. Such power sources must be able to withstand large mechanical strains and still maintain function. Here we report a highly stretchable H3PO4-poly(vinyl alcohol) (PVA) polymer electrolyte obtained by optimizing the polymer molecular weight and its weight ratio to H3PO4 in terms of conductivity and mechanical properties. The electrolyte demonstrates a high conductivity of 3.4 × 10(-3) S cm(-1), and a high fracture strain at 410% elongation. It is mechanically robust with a tensile strength of 2 MPa and a Youngs modulus of 1 MPa, and displays a small plastic deformation (5%) after 1000 stretching cycles at 100% strain. A stretchable supercapacitor device has been developed based on buckled polypyrrole electrodes and the polymer electrolyte. The device shows only a small capacitance loss of 5.6% at 30% strain, and can retain 81% of the initial capacitance after 1000 cycles of such stretching.

Manganese dioxide-anchored three-dimensional nitrogen-doped graphene hybrid aerogels as excellent anode materials for lithium ion batteries

The capacity of manganese dioxide (MnO2) deteriorates with cycling due to the irreversible changes induced by the repeated lithiation and delithiation processes. To overcome this drawback, MnO2/nitrogen-doped graphene hybrid aerogels (MNGAs) were prepared via a facile redox process between KMnO4 and carbon within nitrogen-doped graphene hydrogels. The three-dimensional nitrogen-doped graphene hydrogels were prepared and utilized as matrices for MnO2 deposition. The MNGAs-120 obtained after a deposition time of 120 min delivered a very high discharge capacity of 909 mA h g−1 after 200 cycles at a current density of 400 mA g−1, in sharp contrast to only 280 and 70 mA h g−1 delivered from nitrogen-doped graphene aerogels and MnO2. This discharge capacity is superior to that of the previously reported MnO2/carbon based hybrid materials. This material also exhibited an excellent rate capability and cycling performance. Its superior electrochemical performance can be ascribed to the synergistic interaction between uniformly dispersed MnO2 particles with high capacity and the conductive three-dimensional nitrogen-doped graphene network with a large surface area and an interconnected porous structure.

A highly nitrogen-doped porous graphene – an anode material for lithium ion batteries

A novel nitrogen-doped porous graphene material (NPGM) was prepared by freeze-drying a graphene/melamine–formaldehyde hydrogel and subsequent thermal treatment. The use of melamine–formaldehyde resin as a cross-linking agent and nitrogen source enhances the nitrogen content. NPGM possesses a hierarchical porous structure, a large Brunauer–Emmett–Teller surface area (up to 1170 m2 g−1), and a considerable nitrogen content (5.8 at%). NPGM displays a discharge capacity of 672 mA h g−1 at a current density of 100 mA g−1 when used as an anode material for lithium ion batteries, much higher than that observed for a nitrogen-free graphene porous material (450 mA h g−1). The NPGM electrode also possesses superior cycle stability. No capacity loss was observed even after 200 charge/discharge cycles at a current density of 400 mA g−1. The enhanced electrochemical performance is attributed to nitrogen doping, high specific surface area, and the three-dimensional porous network structure.

Flexible free-standing graphene paper with interconnected porous structure for energy storage

A novel porous graphene paper is prepared via freeze drying a wet graphene oxide gel, followed by thermal and chemical reduction. The macroscopic structure of the formed graphene paper can be tuned by the water content in the gel precursor. With 92% water content, an interconnected macroporous network can be formed. This porous graphene (PG) paper exhibits excellent electrochemical properties. It can deliver a high discharge capacity of 420 mA h g−1 at a current density of 2000 mA g−1 when used as binder-free lithium ion battery anode. PG paper exhibits a specific capacitance of 137 F g−1 at 1 A g−1 in a flexible all-solid-state supercapacitor with PVA/H2SO4 electrolyte. It can maintain 94% of its capacitance under bending. This electrochemical performance and mechanical flexibility makes it an excellent material for flexible energy storage devices.

Graphene cryogel papers with enhanced mechanical strength for high performance lithium battery anodes

A porous graphene paper was prepared by pressing a graphene cryogel, followed by thermal reduction at 220 °C. The cryogel was formed by freeze-drying a solution containing chemically reduced graphene and graphene oxide (CRG/GO). The formed graphene cryogel papers deliver a much higher discharge capacity and rate capability than that from conventional graphene papers fabricated by filtration. These new structures have a discharge capacity higher than 400 mA h g−1 at a current density of 2000 mA g−1 in sharp contrast to 229 mA h g−1 at 50 mA g−1 obtained from conventional graphene papers. These greatly improved electrochemical properties may be attributed to the porous structure and the concomitant high surface area. The mechanical properties may be tuned with the CRG/GO ratio. At a CRG/GO mass ratio of 2:1 the graphene paper has a Youngs modulus nearly 9 times greater than an equivalent paper made from pure GO.

One-Step Synthesis of Graphene/Polypyrrole Nanofiber Composites as Cathode Material for a Biocompatible Zinc/Polymer Battery

The significance of developing implantable, biocompatible, miniature power sources operated in a low current range has become manifest in recent years to meet the demands of the fast-growing market for biomedical microdevices. In this work, we focus on developing high-performance cathode material for biocompatible zinc/polymer batteries utilizing biofluids as electrolyte. Conductive polymers and graphene are generally considered to be biocompatible and suitable for bioengineering applications. To harness the high electrical conductivity of graphene and the redox capability of polypyrrole (PPy), a polypyrrole fiber/graphene composite has been synthesized via a simple one-step route. This composite is highly conductive (141 S cm(-1)) and has a large specific surface area (561 m(2) g(-1)). It performs more effectively as the cathode material than pure polypyrrole fibers. The battery constructed with PPy fiber/reduced graphene oxide cathode and Zn anode delivered an energy density of 264 mWh g(-1) in 0.1 M phosphate-buffer saline.

A facile approach for fabrication of mechanically strong graphene/polypyrrole films with large areal capacitance for supercapacitor applications

Substantial progress has been made in free-standing flexible graphene-based films for flexible supercapacitors. However, there are limited reports on the areal capacitance of these electrodes, which is an important parameter for practical applications, especially in miniaturized electronic devices. Herein we report the facile fabrication of robust flexible graphene/polypyrrole nanoparticle films. PPy NPs act as the “spacer” between graphene layers creating hierarchical structures. This free-standing film shows excellent mechanical properties with a fracture strength of 16.89 MPa and Youngs modulus of 11.77 MPa. The resulting film electrode delivers a large areal specific capacitance of 216 mF cm−2, which is higher or comparable to other graphene/conducting polymer composite films. Moreover, this composite film exhibits a high capacitance retention rate of 87% after 5000 charge/discharge cycles and a fast relaxation time constant of 2.51 s. These excellent properties all suggest their prospective use in flexible energy storage devices.

A Cytocompatible Robust Hybrid Conducting Polymer Hydrogel for Use in a Magnesium Battery.

A cytocompatible robust hybrid conducting-polymer hydrogel, polypyrrole/poly(3,4-ethylenedioxythiophene) is developed. This hydrogel is suitable for electrode-cellular applications. It demonstrates a high battery performance when coupled with a bioresorbable Mg alloy in phosphate-buffered saline. A combination of suitable mechanical and electrochemical properties makes this hydrogel a promising material for bionic applications.

Novel reversible and switchable electrolytes based on magneto-rheology

Replacing organic liquid electrolytes with solid electrolytes has led to a new perspective on batteries, enabling high-energy battery chemistry with intrinsically safe cell designs. However, most solid/gel electrolytes are easily deformed; under extreme deformation, leakage and/or short-circuiting can occur. Here, we report a novel magneto-rheological electrolyte (MR electrolyte) that responds to changes in an external magnetic field; the electrolyte exhibits low viscosity in the absence of a magnetic field and increased viscosity or a solid-like phase in the presence of a magnetic field. This change from a liquid to solid does not significantly change the conductivity of the MR electrolyte. This work introduces a new class of magnetically sensitive solid electrolytes that can enhance impact resistance and prevent leakage from electronic devices through reversible active switching of their mechanical properties.

Electrical Stimulation with a Conductive Polymer Promotes Neurite Outgrowth and Synaptogenesis in Primary Cortical Neurons in 3D

Deficits in neurite outgrowth and synaptogenesis have been recognized as an underlying developmental aetiology of psychosis. Electrical stimulation promotes neuronal induction including neurite outgrowth and branching. However, the effect of electrical stimulation using 3D electrodes on neurite outgrowth and synaptogenesis has not been explored. This study examined the effect of 3D electrical stimulation on 3D primary cortical neuronal cultures. 3D electrical stimulation improved neurite outgrowth in 3D neuronal cultures from both wild-type and NRG1-knockout (NRG1-KO) mice. The expression of synaptophysin and PSD95 were elevated under 3D electrical stimulation. Interestingly, 3D electrical stimulation also improved neural cell aggregation as well as the expression of PSA-NCAM. Our findings suggest that the 3D electrical stimulation system can rescue neurite outgrowth deficits in a 3D culturing environment, one that more closely resembles the in vivo biological system compared to more traditionally used 2D cell culture, including the observation of cell aggregates as well as the upregulated PSA-NCAM protein and transcript expression. This study provides a new concept for a possible diagnostic platform for neurite deficits in neurodevelopmental diseases, as well as a viable platform to test treatment options (such as drug delivery) in combination with electrical stimulation.