Yabin Zhang

Engineering metal organic framework derived 3D nanostructures for high performance hybrid supercapacitors

Metal–organic frameworks (MOFs) have demonstrated great promise as a new platform for the synthesis of porous electrode materials for energy storage. Research effort on MOFs and MOF derived nanostructures has focused mainly on tuning the chemical composition at the molecular level and developing highly porous frameworks in which enhancing the capacity and reducing the transport path of ions are favorable. Here we report an approach using the MOF (polyhedral ZIF-8) as a novel precursor to synthesize two electrode materials with different energy-storage mechanisms: the capacitor-like porous carbon polyhedra and the battery-like MoS2–ZIF composite. The porous carbon polyhedra have a continuous 3D porous network with an extremely high surface area of 3680.6 m2 g−1 and a well-controlled pore size distribution, and the MoS2–ZIF composite shows a three-dimensional (3D) nanostructure with an open framework. Furthermore, a novel hybrid supercapacitor is fabricated by employing these two 3D nanostructured MOF-derived electrode materials, which shows the best properties among the current hybrid supercapacitors with respect to energy, power and cycling life. The presented strategy for the controlled design and synthesis of 3D MOF-derived nanostructures provides prospects in developing high-performance active materials in advanced energy storage devices.

Elucidating the Intercalation Pseudocapacitance Mechanism of MoS2–Carbon Monolayer Interoverlapped Superstructure: Toward High-Performance Sodium-Ion-Based Hybrid Supercapacitor

Two-dimensional (2D) layered materials have shown great promise for electrochemical energy storage applications. However, they are usually limited by the sluggish kinetics and poor cycling stability. Interface modification on 2D layered materials provides an effective way for increasing the active sites, improving the electronic conductivity, and enhancing the structure stability so that it can potentially solve the major issues on fabricating energy storage devices with high performance. Herein, we synthesize a novel MoS2-carbon (MoS2-C) monolayer interoverlapped superstructure via a facile interface-modification route. This interlayer overlapped structure is demonstrated to have a wide sodium-ion intercalation/deintercalation voltage range of 0.4-3.0 V and the typical pseudocapacitive characteristics in fast kinetics, high reversibility, and robust structural stability, thus displaying a large reversible capacity, a high rate capability, and an improved cyclability. A full cell of sodium-ion hybrid supercapacitor based on this MoS2-C hybrid architecture can operate up to 3.8 V and deliver a high energy density of 111.4 Wh kg-1 and a high power density exceeding 12u202f000 W kg-1. Furthermore, a long cycle life of 10u202f000 cycles with over 77.3% of capacitance retention can be achieved.

Graphene-coupled Ti3C2 MXenes-derived TiO2 mesostructure: promising sodium-ion capacitor anode with fast ion storage and long-term cycling

Sodium-ion-based capacitors and batteries are considered as a low-cost energy storage technology alternative to their lithium-ion counterparts owing to the abundance of sodium in Earth. Their widespread use is however limited by the lack of high-performance electrode materials. In this work, we report that MXenes-Ti3C2 can be oxidized into a Ti-peroxo complex gel at room temperature by simply adding H2O2, from concentrated to dilute. The highly water-soluble property of this gel allows the synthesis of a graphene-supported TiO2 nanocomposite with highly porous nano-/meso-hybrid architecture via a more facile and environmentally friendly way. The unique hybrid architecture of the produced TiO2–RGO nanocomposite results in pseudocapacitive behavior in Na+ charge storage with high reversibility, fast kinetics, long cyclability, and negligible degradation to the parent structure. By incorporating the TiO2–RGO composite as the anode, a novel sodium-ion capacitor is constructed that is capable of operating at a high voltage of 4.0 V and delivering a maximum energy density of 94.7 W h kg−1, which is comparable to lithium-ion based capacitors. The approach reported here could be potentially extended for fabricating a host of MXenes-derived metal oxide nanomaterials or nanocomposites for numerous applications, particularly in view of the expanding MXenes portfolio.

Highly porous carbon with large electrochemical ion absorption capability for high-performance supercapacitors and ion capacitors

Carbon-based supercapacitors have attracted extensive attention as the complement to batteries, owing to their durable lifespan and superiority in high-power-demand fields. However, their widespread use is limited by the low energy storage density; thus, a high-surface-area porous carbon is urgently needed. Herein, a highly porous carbon with a Brunauer-Emmett-Teller specific surface area up to 3643 m2 g-1 has been synthesized by chemical activation of papayas for the first time. This sp2-bonded porous carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form narrow mesopores of 2xa0∼xa05 nm in width, which can be systematically tailored with varied activation levels. Two-electrode symmetric supercapacitors constructed by this porous carbon achieve energy density of 8.1 Wh kg-1 in aqueous electrolyte and 65.5 Wh kg-1 in ionic-liquid electrolyte. Furthermore, half-cells (versus Li or Na metal) using this porous carbon as ion sorption cathodes yield high specific capacity, e.g., 51.0 and 39.3 mAh g-1 in Li+ and Na+ based organic electrolyte. These results underline the possibility of obtaining the porous carbon for high-performance carbon-based supercapacitors and ion capacitors in a readily scalable and economical way.

Recent progress on micro- and nano-robots: towards in vivo tracking and localization

Scientists have dreamed for long of miniature robots that can be controlled and navigated inside human body, to help the medical doctors to diagnose and treat the diseases.