Freestanding, robust electrodes with high capacity and long lifetime are of critical importance to the development of advanced lithium-sulfur (Li-S) batteries for next-generation electronics, whose potential applications are greatly limited by the lithium polysulfide (LiPS) shuttle effect. Solutions to this issue have mostly focused on the design of cathode hosts with a polar, sulfurphilic, conductive network, or the introduction of an extra layer to suppress LiPS shuttling, which either results in complex fabrication procedures or compromises the mechanical flexibility of the device. A robust Ti 3 C 2 T x /S conductive paper combining the excellent conductivity, mechanical strength, and unique chemisorption of LiPSs from MXene nanosheets is reported. Importantly, repeated cycling initiates the in situ formation of a thick sulfate complex layer on the MXene surface, which acts as a protective membrane, effectively suppressing the shuttling of LiPSs and improving the utilization of sulfur. Consequently, the Ti 3 C 2 T x /S paper exhibits a high capacity and an ultralow capacity decay rate of 0.014% after 1500 cycles, the lowest value reported for Li-S batteries to date. A robust prototype pouch cell and full cell of Ti 3 C 2 T x /S paper // lithium foil and prelithiated germanium are also demonstrated. The preliminary results show that Ti 3 C 2 T x /S paper holds great promise for future flexible and wearable electronics.

Heterostructures, [1] particularly 2D heterostructures, have shown great potential in the field of catalytic energy conversion due to the fascinating synergism of different components in tuning electronic structures for promoted surface catalysis. [2-5] In typical catalytic reactions, heterostructures always need to be exposed to corrosive liquids and gases to fully interact with the reactants. Therefore, the rational design and synthesis of heterostructures that have rich exposed active sites and highly stable heterointerfaces are rising as an appealing and critical issue in the area of energy conversion. On the other hand, hydrogen generated from electrochemical water splitting is regarded as an ideal alternative to fossil fuels because of its ultrahigh gravimetric energy density, zero-carbon emission, and natural abundance. [6-10] Currently, the alkaline electrolyzers are technically more available for the production of electrocatalytic hydrogen, such as in the water-alkaline electrolysis and in the chloralkaline industry, owing Heterostructures exhibit considerable potential in the field of energy conversion due to their excellent interfacial charge states in tuning the electronic properties of different components to promote catalytic activity. However, the rational preparation of heterostructures with highly active heterosurfaces remains a challenge because of the difficulty in component tuning, morphology control, and active site determination. Herein, a novel heterostructure based on a combination of RuMo nanoalloys and hexagonal N-doped carbon nanosheets is designed and synthesized. In this protocol, metal-containing anions and layered double hydroxides are employed to control the components and morphology of heterostructures, respectively. Accordingly, the as-made RuMo-nanoalloysembedded hexagonal porous carbon nanosheets are promising for the hydrogen evolution reaction (HER), resulting in an extremely small overpotential (18 mV), an ultralow Tafel slope (25 mV dec −1), and a high turnover frequency (3.57 H 2 s −1) in alkaline media, outperforming current Ru-based electrocatalysts. Firstprinciple calculations based on typical 2D N-doped carbon/RuMo nanoalloys heterostructures demonstrate that introducing N and Mo atoms into C and Ru lattices, respectively, triggers electron accumulation/depletion regions at the heterosurface and consequently reduces the energy barrier for the HER. This work presents a convenient method for rational fabrication of carbon-metal heterostructures for highly efficient electrocatalysis.

A closed-loop and self-adaptive cardiac optogenetics is realized by a negative stretching-resistive strain sensor.

Implantable brain–computer interface (BCI) devices are an effective tool to decipher fundamental brain mechanisms and treat neural diseases. However, traditional neural implants with rigid or bulky cross-sections cause trauma and decrease the quality of the neuronal signal. Here, we propose a MEMS-fabricated flexible interface device for BCI applications. The microdevice with a thin film substrate can be readily reduced to submicron scale for low-invasive implantation. An elaborate silicon shuttle with an improved structure is designed to reliably implant the flexible device into brain tissue. The flexible substrate is temporarily bonded to the silicon shuttle by polyethylene glycol. On the flexible substrate, eight electrodes with different diameters are distributed evenly for local field potential and neural spike recording, both of which are modified by Pt-black to enhance the charge storage capacity and reduce the impedance. The mechanical and electrochemical characteristics of this interface were investigated in vitro. In vivo, the small cross-section of the device promises reduced trauma, and the neuronal signals can still be recorded one month after implantation, demonstrating the promise of this kind of flexible BCI device as a low-invasive tool for brain–computer communication.

Two-dimensional (2D) porous carbon nanosheets (2DPCs) have attracted great attention for their good porosity and long-distance conductivity.F actors such as templates, precursors, andc arbonization-activation methods, directly determine their performance. However,r ational design and preparation of porous carbon materials with controlled 2D morphology and heteroatom dopants remains ac hallenge. Therefore, an ionic polyimide with both sp 2 -a nd sp 3 -hybridized nitrogen atoms was prepared as ap recursor for fabricating N-doped hexagonal porousc arbon nanosheets through ah ard-templatea pproach. Because of the large surface area and efficient charge-mass transport, the resulting activated 2D porous carbon nanosheets (2DPCs-a) displayed promising electrocatalytic properties for oxygen reduction reaction( ORR) in alkaline and acidic media, such as ultralow half-wavep otential( 0.83 vs. 0.84 VofP t/C) and superior limiting current density (5.42 vs. 5.14 mA cm À2 of Pt/C). As air cathodes in Zn-air batteries, the as-developed 2DPCs-a exhibited long stabilitya nd high capacity (up to 614 mA hg À1 ), which are both highert han those of commercial Pt/C. This work provides ac onvenient methodf or controllable and scalable2 DPCs fabrication as well as new opportunities to develop high-efficiency electrocatalysts for ORR and Zn-air batteries.Scheme1.Schematicof2 DPCs preparation basedo ni onic polyimide precursorand LDH template:(i) polymerization of PMDA and Vio-NH 2 through solvothermal reactioni ndimethylformamide at 180 8Cfor 10 h; (ii)carbonization of IPI@LDH at 800 8Cfor 2hin N 2 atmosphere; and (iii)etching with KOH at 180 8Cf or 20 hand HCla t8 08Cfor 12 h. Figure 3. ORR performance of as-prepared samples in O 2 -saturated 0.1 m KOH. (a) CV curves, (b) LSV polarization curves, and (c)T afel plots of 2DPCs, PCs and Pt/C. (d) Calculated potential dependent electron transfer number and hydrogenp eroxide percentage; (e) K-L plots (J À1 vs. w À1/2 )of2 DPCs-a at different potentials;(f) Current-time (i-t)c hronoamperometric responsesa t0 .75 Vatar otationr ate of 1600 rpm. RHE = reversible hydrogen electrode.Figure 6. (a) SEM and (b) TEM images of 2DPCs-a after 10 hstability test as air cathode in Zn-air battery. (c) High-resolution N1sc ore-level XPS spectrum and corresponding (d) atomic percentages of nitrogen species in 2DPCS-a' compared with 2DPCs-a.