Multifunctional Mesoporous Polyaniline/Graphene Nanosheets for Flexible Planar Integrated Microsystem of Zinc Ion Microbattery and Gas Sensor.

The prosperity of smart portable microdevices urgently requires an advanced integrated microsystem equipped with cost-effective safe microbatteries and ultra-stable sensitive sensors. However, the practical application of smart microdevices is limited by complex active materials with single function. Here, the two-dimensional (2D) mesoporous nanosheets of polyaniline decorated on graphene with large specific surface area of 141 m2  g-1 , ample active sites, comparable conductivity, and ordered mesopores of 18 nm for a new-type co-planar integrated microsystem of zinc ion microbattery and gas sensor are developed. These unique triple-function mesoporous nanosheets are well proved for dendrite-free zinc anode with long cyclability (>500 h) and small overpotential (48 mV), a high performance cathode of zinc ion microbattery with outstanding volumetric capacity of 78 mAh cm-3 outperforming their counterparts reported, and a highly sensitive gas sensor with a resistance response (ΔR/R0 %) of 118% for 20 ppm NH3 . Moreover, the co-planar battery-sensor integrated microsystem exhibits superior mechanical stability and smart integration. Therefore, this work will open many opportunities to develop multifunctional 2D mesoporous materials for high performance smart integrated microsystems.

Achieving stable Na metal cycling via polydopamine/multilayer graphene coating of a polypropylene separator.

Sodium metal batteries are considered one of the most promising low-cost high-energy-density electrochemical energy storage systems. However, the growth of unfavourable Na metal deposition and the limited cell cycle life hamper the application of this battery system at a large scale. Here, we propose the use of polypropylene separator coated with a composite material comprising polydopamine and multilayer graphene to tackle these issues. The oxygen- and nitrogen- containing moieties as well as the nano- and meso- porous network of the coating allow cycling of Na metal electrodes in symmetric cell configuration for over 2000 h with a stable 4 mV overpotential at 1 mA cm-2. When tested in full Na || Na3V2(PO4)3 coin cell, the coated separator enables the delivery of a stable capacity of about 100 mAh g-1 for 500 cycles (90% capacity retention) at a specific current of 235 mA g-1 and satisfactory rate capability performances (i.e., 75 mAh g-1 at 3.5 A g-1).

3D Flexible, Conductive, and Recyclable Ti3C2Tx MXene-Melamine Foam for High-Areal-Capacity and Long-Lifetime Alkali-Metal Anode.

Alkali metals are ideal anodes for high-energy-density rechargeable batteries, while seriously hampered by limited cycle life and low areal capacities. To this end, rationally designed frameworks for dendrite-free and volume-changeless alkali-metal deposition at both high current densities and capacities are urgently required. Herein, a general 3D conductive Ti3C2TX MXene-melamine foam (MXene-MF) is demonstrated as an elastic scaffold for dendrite-free, high-areal-capacity alkali anodes (Li, Na, K). Owing to the lithiophilic nature of F-terminated MXene, conductive macroporous network, and excellent mechanical toughness, the constructed MXene-MF synchronously achieves a high current density of 50 mA cm-2 for Li plating, high areal capacity (50 mAh cm-2) with high Coulombic efficiency (99%), and long lifetime (3800 h), surpassing the Li anodes reported recently. Meanwhile, MXene-MF shows flat voltage profiles for 720 h at 10 mA cm-2 for the Na anode and 800 h at 5 mA cm-2 for the K anode, indicative of the wide applicability. Notably, the high current density of 20 mA cm-2 for 20 mAh cm-2 for the Na anode, accompanying good recyclability was rarely achieved before. When coupled with sulfur or Na3V2(PO4)3 cathodes, the assembled MXene-MF alkali (Li, Na)-based full batteries showcase enhanced rate capability and cycling stability, demonstrating the potential of MXene-MF for advanced alkali-metal batteries.

Conducting and Lithiophilic MXene/Graphene Framework for High-Capacity, Dendrite-Free Lithium-Metal Anodes.

Li-metal anode is widely acknowledged as the ideal anode for high-energy-density batteries, but seriously hindered by the uncontrollable dendrite growth and infinite volume change. Toward this goal, suitable stable scaffolds for dendrite-free Li anodes with large current density (>5 mA cm-2) and high Li loading (>90%) are highly in demand. Herein, a conductive and lithiophilic three-dimensional (3D) MXene/graphene (MG) framework is demonstrated for a dendrite-free Li-metal anode. Benefiting from its high surface area (259 m2 g-1) and lightweight nature with uniformly dispersed lithiophilic MXene nanosheets as Li nucleation sites, the as-formed 3D MG scaffold showcases an ultrahigh Li content (∼92% of the theoretical capacity), as well as strong capabilities in suppressing the Li-dendrite formation and accommodating the volume changes. Consequently, the MG-based electrode exhibits high Coulombic efficiencies (∼99%) with a record lifespan up to 2700 h and is stable for 230 cycles at an ultrahigh current density of 20 mA cm-2. When coupled with Li4Ti5O12 or sulfur, the MG-Li/Li4Ti5O12 full-cell offers an enhanced capacity of 142 mAh g-1 after 450 cycles, while the MG-Li/sulfur cell delivers an improved rate performance, implying the great potential of this 3D MG framework for building long-lifetime, high-energy-density batteries.

Synthesis of Si, N co-Doped Nano-Sized TiO2 with High Thermal Stability and Photocatalytic Activity by Mechanochemical Method.

Τhe photocatalytic activity in the range of visible light wavelengths and the thermal stability of the structure were significantly enhanced in Si, N co-doped nano-sized TiO2, and synthesized through high-energy mechanical milling of TiO2 and SiO2 powders, which was followed by calcination at 600 °C in an ammonia atmosphere. High-energy mechanical milling had a pronounced effect on the mixing and the reaction between the starting powders and greatly favored the transformation of the resultant powder mixture into an amorphous phase that contained a large number of evenly-dispersed nanocrystalline TiO2 particles as anatase seeds. The experimental results suggest that the elements were homogeneously dispersed at an atomic level in this amorphous phase. After calcination, most of the amorphous phase was crystallized, which resulted in a unique nano-sized crystalline-core/disordered-shell morphology. This novel experimental process is simple, template-free, and provides features of high reproducibility in large-scale industrial production.