The effective implantation of conductive and charge storage materials into flexible frames has been strongly demanded for the development of flexible supercapacitors. Here, we introduce metallic cellulose paper-based supercapacitor electrodes with excellent energy storage performance by minimizing the contact resistance between neighboring metal and/or metal oxide nanoparticles using an assembly approach, called ligand-mediated layer-by-layer assembly. This approach can convert the insulating paper to the highly porous metallic paper with large surface areas that can function as current collectors and nanoparticle reservoirs for supercapacitor electrodes. Moreover, we demonstrate that the alternating structure design of the metal and pseudocapacitive nanoparticles on the metallic papers can remarkably increase the areal capacitance and rate capability with a notable decrease in the internal resistance. The maximum power and energy density of the metallic paper-based supercapacitors are estimated to be 15.1 mW cm−2 and 267.3 μWh cm−2, respectively, substantially outperforming the performance of conventional paper or textile-type supercapacitors.

Electrical communication between an enzyme and an electrode is one of the most important factors in determining the performance of biofuel cells. Here, we introduce a glucose oxidase-coated metallic cotton fiber-based hybrid biofuel cell with efficient electrical communication between the anodic enzyme and the conductive support. Gold nanoparticles are layer-by-layer assembled with small organic linkers onto cotton fibers to form metallic cotton fibers with extremely high conductivity (>2.1×104 S cm−1), and are used as an enzyme-free cathode as well as a conductive support for the enzymatic anode. For preparation of the anode, the glucose oxidase is sequentially layer-by-layer-assembled with the same linkers onto the metallic cotton fibers. The resulting biofuel cells exhibit a remarkable power density of 3.7 mW cm−2, significantly outperforming conventional biofuel cells. Our strategy to promote charge transfer through electrodes can provide an important tool to improve the performance of biofuel cells.

Achieving high energy storage performance and fast rate capability at the same time is one of the most critical challenges in battery technology. Here, a high‐performance textile cathode with notable specific/areal capacities and high rate capability through an interfacial interaction‐mediated assembly that can directly bridge all interfaces existing between textile and conductive materials and between conductive and active materials, minimizing unnecessary insulating organics is reported. First, amine (NH2)‐ and carboxylic acid (COOH)‐functionalized multiwalled carbon nanotubes (MWNTs) are alternately layer‐by‐layer (LbL)‐assembled onto cellulose textiles for the preparation of conductive textiles using hydrogen bonding interactions. Dioleamide‐stabilized LiFePO4 nanoparticles (DA‐LFP NPs) with high crystallinity and high dispersion stability in organic media are consecutively LbL‐assembled with MWNT‐NH2 onto conductive textiles through ligand replacement between native DA ligands bound to the surface of the LFP NPs and NH2 groups of MWNTs. In this case, 35 nm sized LFP NPs are densely and uniformly adsorbed onto all regions of the textile, and additionally, their areal capacities are increased according to the deposition number without a significant loss of charge transfer kinetics. The formed textile cathodes exhibit remarkable specific/areal capacities (196 mAh g−1/8.3 mAh cm−2 at 0.1 C) and high rate capability with highly flexible mechanical properties.

Development of soft actuators with higher performance and more versatile controllability has been strongly required for further innovative advancement of various soft applications. Among various soft actuators, electrochemical actuators have attracted much attention due to their lightweight, simple device configuration, and facile low-voltage control. However, the reported performances have not been satisfactory because their working mechanism depends on the limited electrode expansion by conventional electrochemical reactions. Herein, we report an electroosmosis-driven hydrogel actuator with a fully soft monolithic structure-based whole-body actuation mechanism using an amphiphilic interaction-induced layer-by-layer assembly. For this study, cracked electrodes with interconnected metal nanoparticles are prepared on hydrogels through layer-by-layer assembly and shape transformation of metal nanoparticles at hydrophobic/hydrophilic solvent interfaces. Electroosmotic pumping by cracked electrodes instantaneously induces hydrogel swelling through reversible and substantial hydraulic flow. The resultant actuator exhibits actuation strain of higher than 20% and energy density of 1.06 × 105 J m–3, allowing various geometries (e.g., curved-planar and square-pillared structures) and motions (e.g., slow-relaxation, spring-out, and two degree of freedom bending). In particular, the energy density of our actuators shows about 10-fold improvement than those of skeletal muscle, electrochemical actuators, and various stimuli-responsive hydrogel actuators reported to date.

The design of electrode with high volumetric performance in energy storages still remains as a significant challenge because it simultaneously requires a high packing density of active materials for high energy density and a conductive porous structure for facile charge transfer. Here, a novel assembly process is introduced for thin-film anodes for Li-ion battery with a high volumetric energy density and rate performance by systematically controlling the interfacial structure between metal-oxide nanoparticles and/ or metal clusters. For this study, oleic-acid-stabilized Fe 3 O 4 nanoparticles are layer-by-layer assembled with small organic molecules through a ligand exchange reaction, which enable a high packing density. During layer-by-layer deposition, periodic Pt-sputtering onto multilayers significantly reduces the internal resistance of the electrodes but maintains the nanopores formed among the nanoparticles. The resulting anode exhibits an extremely high volumetric capacity of ≈3195 mA h cm −3 and rate performance, which are far superior to that reported for Li-ion battery anodes. Additionally, all components in the electrodes have a stable covalent bond network between the metal atom and the amine group of organic molecule linker, allowing good cycle retention. This approach can be widely applied to the fabrication of various nanoparticle-based electrodes, enabling maximum charge storage performance in confined volumes.