Natural leaves, with elaborate architectures and functional components, harvest and convert solar energy into chemical fuels that can be converted into energy based on photosynthesis. The energy produced leads to work done that inspired many autonomous systems such as light-triggered motion. On the basis of this nature-inspired phenomenon, we report an unprecedented bilayer-structured actuator based on MXene (Ti3C2Tx)–cellulose composites (MXCC) and polycarbonate membrane, which mimic not only the sophisticated leaf structure but also the energy-harvesting and conversion capabilities. The bilayer actuator features multiresponsiveness, low-power actuation, fast actuation speed, large-shape deformation, programmable adaptability, robust stability, and low-cost facile fabrication, which are highly desirable for modern soft actuator systems. We believe that these adaptive soft systems are attractive in a wide range of revolutionary technologies such as soft robots, smart switch, information encryption, infrared dynamic display, camouflage, and temperature regulation, as well as human-machine interface such as haptics.

Electrically activated soft actuators with large deformability are important for soft robotics but enhancing durability and efficiency of electrochemical actuators is challenging. Herein, we demonstrate that the actuation performance of an ionic two-dimensional covalent-organic framework based electrochemical actuator is improved through the ordered pore structure of opening up efficient ion transport routes. Specifically, the actuator shows a large peak to peak displacement (9.3 mm, ±0.5 V, 1 Hz), a fast-response time to reach equilibrium-bending (~1 s), a correspondingly high bending strain difference (0.38%), a broad response frequency (0.1–20 Hz) and excellent durability (>99%) after 23,000 cycles. The present study ascertains the functionality of soft electrolyte as bionic artificial actuators while providing ideas for expanding the limits in applications for robots.

Conductive polymer (e.g., polyaniline and polypyrrole)-based ECAs can generate high actuation strains due to large volume change induced by the doping/dedoping during the faradaic charge and discharge process, [3] but usually show limited cycling stability and decreased response under high frequencies/rates. [1] Many conductive inorganic materials have also been studied as active materials for ECAs, including 0D metal nanoparticles (e.g., Au and Pt) and carbon black, [4][5][6] 1D carbon nanotubes and nanofibers (CNTs and CNFs), [1,[7][8][9] as well as 2D graphene, [10][11][12][13][14][15] graphdiyne, [10] black phosphorous (BP), [32] and MoS 2 . [16] However, 0D metal nanoparticle and carbon-black-based electrodes show limited specific capacitance, poor toughness, and low stiffness, limiting the deformation, cycling life, and output force. 1D CNT and CNF-based electrodes can have better mechanical performance but show small volumetric capacitance restricting the actuation strain. Atomically thin 2D nanomaterial (such as graphene)-based electrodes can have significantly higher specific capacitance while maintaining a good mechanical strength and modulus, hence they are very promising for fabricating high-performance ECAs.Recently, 2D Ti 3 C 2 T x (T = OH, O, and F) MXene derived from Ti 3 C 2 Al has also attracted researchers' attention for ECA applications, [17][18][19][20] due to its ultrahigh electrical conductivity, [21] high mechanical performance, [22] and large volumetric specific capacitance. [23,24] Come et al. found that a Ti 3 C 2 T x paper undergoes a large contraction along the thickness direction during charge in a Li 2 SO 4 solution, accompanied by a ≈2.1% shrinkage of layer distance between MXene sheets. [20] This large volume change during charge and discharge renders MXene as a good active material for ECAs. Pang et al. showed that a MXenebased ECA with a poly(vinyl alcohol) (PVA)/H 2 SO 4 gel electrolyte generated a peak-to-peak strain difference of 0.26% under a triangular wave voltage of ±1 V and 1 mHz, which was ascribed to the expansion and shrinkage of the interlayer spacing during charge and discharge. However, the actuation at high frequency is undesirable due to limited ion diffusion across the film. Wang et al. fabricated a 3D structured polystyrene (PS) microsphere/MXene composite-based ECA, which generated a peakto-peak strain difference of 1.18% under a square wave voltage of ±1.5 V and 0.1 Hz due to the much enhanced ion diffusion by the PS. However, the introduction of PS microspheres decreased the tensile strength and Young's modulus of the composite and the resulting ECA. In these cases, the Young's Ti 3 C 2 T x MXene film is promising for electrochemical actuators due to its high electrical conductivity and volumetric capacitance. However, its actuation performance is limited by the slow ion diffusion through the film and poor mechanical property in aqueous electrolytes. Here, molecular-level methylcellulose (MC)/MXene hybrid films are assembled with obviously enlarged layer dis...

The rational design of previously unidentified materials that could realize excellent electrochemical-controlled optical and charge storage properties simultaneously, are especially desirable and useful for fabricating smart multifunctional devices. Here, a facile synthesis of a 1D-d conjugated coordination polymer (Ni-BTA) is reported, consisting of metal (Ni)-containing nodes and organic linkers (1,2,4,5-benzenetetramine), which could be easily grown on various substrates via a scalable chemical bath deposition method. The resulting Ni-BTA film exhibits superior performances for both electrochromic and energy storage functions, such as large optical modulation (61.3%), high coloration efficiency (223.6 cm 2 C −1), and high gravimetric capacity (168.1 mAh g −1). In particular, the Ni-BTA film can maintain its electrochemical recharge-ability and electrochromic properties even after 10 000 electrochemical cycles demonstrating excellent durability. Moreover, a smart energy storage indicator is demonstrated in which the energy storage states can be visually recognized in real time. The excellent electrochromic and charge storage performances of Ni-BTA films present a great promise for Ni-BTA nanowires to be used as practical electrode materials in various applications such as electrochromic devices, energy storage cells, and multifunctional smart windows.

• Downsizing of MnS and encapsulating by conductive N, S-co-doped carbon matrix (MnS@NSC) provide excellent reversible capacity, rate capability, and cycling stability in sodium-based electrolyte. • The charge storage mechanism of MnS@NSC was analyzed, showing pseudocapacitive control behavior. • The as-fabricated sodium-ion capacitor delivers excellent electrochemical performance. ABSTRACT Sodium-ion capacitors (SICs) have received increasing interest for grid stationary energy storage application due to their affordability, high power, and energy densities. The major challenge for SICs is to overcome the kinetics imbalance between faradaic anode and nonfaradaic cathode. To boost the Na + reaction kinetics, the present work demonstrated a high-rate MnS-based anode by embedding the MnS nanocrystals into the N, S-co-doped carbon matrix (MnS@NSC). Benefiting from the fast pseudocapacitive Na + storage behavior, the resulting composite exhibits extraordinary rate capability (205.6 mAh g −1 at 10 A g −1) and outstanding cycling stability without notable degradation after 2000 cycles. A prototype SIC was demonstrated using MnS@NSC anode and N-doped porous carbon (NC) cathode; the obtained hybrid SIC device can display a high energy density of 139.8 Wh kg −1 and high power density of 11,500 W kg −1 , as well as excellent cyclability with 84.5% capacitance retention after 3000 cycles. The superior electrochemical performance is contributed to downsizing of MnS and encapsulation of conductive N, S-co-doped carbon matrix, which not only promote the Na + and electrons transport, but also buffer the volume variations and maintain the structure integrity during Na + insertion/extraction, enabling its comparable fast reaction kinetics and cyclability with NC cathode.

Achieving a well tradeoff between electrical and optical performances remains challenging for conventional silver nanowires (AgNWs) random network conductors. An innovative AgNW‐bundle mesh (AgBM) composed of exquisite knots and abundant open area is realized by one‐step spray‐assembly at room temperature, showing high optoelectronic performance. A dynamic assembly mechanism based on the spray assembly of isopropanol‐based AgNWs ink is revealed, ensuring a favorable coffee‐ring effect dominated by the capillary flow rather than Marangoni reflux, driving the AgNWs to deposit at the edges of droplets. The initially formed AgNW‐bundle rings serve as template to constrain the movement of AgNWs from the subsequent droplets, rendering scalable and continuous accumulation of nanowires to produce a connective AgBM. The controlling factors of surface tension of substrates and ink, wettability, spreading and pinning effect of the ink droplets, as well as tunable assembly driving force determined by spraying rate are revealed, realizing an universal spray‐assembly strategy for tailorable fabrication of AgBMs using AgNWs with different sizes in diameter (20–120 nm) and length (20–200 µm). Thicker AgBMs could reduce the sheet resistance without severe sacrifice of transparency. Thinner AgNW‐bundles/knots with better electrical connection can be realized from the finer and longer AgNWs, delivering higher optoelectronic performance.

We rationally synthesized the thermoplastic and hydrophilic poly(urethane-acrylate) (HPUA) binder for a type of printable and stretchable Ag flakes–HPUA (Ag-HPUA) electrodes in which the conductivity can be enhanced by human sweat. In the presence of human sweat, the synergistic effect of Cl− and lactic acid enables the partial removal of insulating surfactant on silver flakes and facilitates sintering of the exposed silver flakes, thus the resistance of Ag-HPUA electrodes can be notably reduced in both relaxed and stretched state. The on-body data show that the resistance of one electrode has been decreased from 3.02 to 0.62 ohm during the subject’s 27-min sweating activity. A stretchable textile sweat-activated battery using Ag-HPUA electrodes as current collectors and human sweat as the electrolyte was constructed for wearable electronics. The enhanced conductivity of the wearable wiring electrode from the reaction with sweat would provide meritorious insight into the design of wearable devices.

The combination of graphene oxide and cellulose produces shape programmable active origamis, which are able to transform among their multi-stable morphs, including 3D soft robotic architectures, mechanical metamaterials and biomimetic analogies.