CitationAll-MXene (2D titanium carbide) solid-state microsupercapacitors for on-chip energy storage 2016 Energy Environ. Sci. On-chip energy storage is a rapidly evolving research topic, opening doors for integration of batteries and supercapacitors at microscales on rigid and flexible platforms. Recently, a new class of two-dimensional (2D) transition metal carbides and nitrides (so-called MXenes) has shown great promise in electrochemical energy storage applications. Here, we report the farbication of all-MXene (Ti3C2Tx) solid-state interdigital microsupercapacitors by employing a solution spray-coating, followed by a photoresist-free direct laser cutting method. Our prototype devices consisted of two layes of Ti3C2Tx with two different flake sizes. The bottom layer was stacked large-size MXene flakes (lateral dimensions of 3-6 μm) serving mainly as current collectors. The top layer was made of small-size MXene flakes (~1 μm) with a large number of defects and edges as the electroactive layer responsible for energy storage. Compared to Ti3C2Tx micro-supercapacitors with platinum current collectors, the all-MXene devices exhibited much lower contact resistance, higher capacitances and better rate-capabilities. The areal and volumetric capacitances of ~27 mF cm -2 and ~357 F cm -3 , respectively, at a scan rate of 20 mV s -1 were achieved. The devices also demonstrated their excellent cyclic stability, with 100 % capacitance retention after 10,000 cycles at a scan rate of 50 mV s -1 . This study opens up a plethora of possible designs for high-performance on-chip devices employing different chemistries, flake sizes and morphologies of MXenes and their heterostructures. Eprint version Broader contextThe continuous development and further miniaturization of portable electronic devices and microelectromechanical systems has led to the increasing demands for micro or nanoscale power sources and energy storage units. Supercapacitors, also called electrochemical capacitors, are energy storage devices with long service life and high power densities that can be fully charged and discharged in seconds. Small-scale supercapacitors, or micro-supercapacitors (MSCs), can be integrated with self-powered microscale devices and provide the required power for a long duration of time without maintenance, serving as ideal stand-alone power sources. The intrinsic properties of electrode materials play a crucially important role in the performance of MSCs. Here, a novel MSC is fabricated by employing a new material, two-dimensional titanium carbide (MXene). The MXene MSCs offer long lifetime and higher areal and volumetric capacities compared to most of the previously reported devices. This work opens up a door for the design of on-chip devices with high energy storage capability by employing a large family (~ 20 members) of 2D MXenes and their heterostructures.

oxide (DOPO) has been grafted onto the surface of graphene oxide (GO) by reacting epoxy ring groups together with the reduced graphene structure (DOPO-rGO). X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and UV− vis spectroscopy confirm that DOPO not only covalently bonded to the GO, as a functionalization moiety, but also partly restored the conjugate structure of GO, as a reducing agent. A pelletlike structure of DOPO on rGO sheets was observed by means of transmission electron microscopy (TEM), contributing to good dispersion of rGO in nonpolar toluene. Furthermore, the flame retardancy and thermal stability of DOPO-rGO/epoxy nanocomposites containing various weight fractions of DOPO-rGO were investigated by the limiting oxygen index (LOI) test and thermogravimetric analysis (TGA) in nitrogen. Significant increases in the char yield and LOI were achieved with the addition of 10 wt % DOPO-rGO in epoxy, giving improvements of 81% and 30%, respectively. DOPO-rGO/epoxy nanocomposites with phosphorus and graphene layer structures were found to contribute to excellent flame retardancy compared to that of neat epoxy. Therefore, the synergestic effect of DOPO-rGO is quite useful, and this material can be utilized as a potential flame retardant.

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The graphene nanosheet electrode with excellent high-rate performance and satisfactory cyclability is an ideal anode for sodium-ion batteries.

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