Nano‐RuO2‐Decorated Holey Graphene Composite Fibers for Micro‐Supercapacitors with Ultrahigh Energy Density

Compactness and versatility of fiber‐based micro‐supercapacitors (FMSCs) make them promising for emerging wearable electronic devices as energy storage solutions. But, increasing the energy storage capacity of microscale fiber electrodes, while retaining their high power density, remains a significant challenge. Here, this issue is addressed by incorporating ultrahigh mass loading of ruthenium oxide (RuO₂) nanoparticles (up to 42.5 wt%) uniformly on nanocarbon‐based microfibers composed largely of holey reduced graphene oxide (HrGO) with a lower amount of single‐walled carbon nanotubes as nanospacers. This facile approach involes (1) space‐confined hydrothermal assembly of highly porous but 3D interconnected carbon structure, (2) impregnating wet carbon structures with aqueous Ru³⁺ ions, and (3) anchoring RuO₂ nanoparticles on HrGO surfaces. Solid‐state FMSCs assembled using those fibers demonstrate a specific volumetric capacitance of 199 F cm^?3 at 2 mV s^?1. Fabricated FMSCs also deliver an ultrahigh energy density of 27.3 mWh cm^?3, the highest among those reported for FMSCs to date. Furthermore, integrating 20 pieces of FMSCs with two commercial flexible solar cells as a self‐powering energy system, a light‐emitting diode panel can be lit up stably. The current work highlights the excellent potential of nano‐RuO₂‐decorated HrGO composite fibers for constructing micro‐supercapacitors with high energy density for wearable electronic devices.     

A TiN Nanorod Array 3D Hierarchical Composite Electrode for Ultrahigh‐Power‐Density Bromine‐Based Flow Batteries

Bromine‐based flow batteries are well suited for stationary energy storage due to attractive features of high energy density and low cost. However, the bromine‐based flow battery suffers from low power density and large materials consumption due to the relatively high polarization of the Br₂/Br^? couple on the electrodes. Herein, a self‐supporting 3D hierarchical composite electrode based on a TiN nanorod array is designed to improve the activity of the Br₂/Br^? couple and increase the power density of the bromine‐based flow battery. In this design, a carbon felt provides a composite electrode with a 3D electron conductive framework to guarantee high electronic conductivity, while the TiN nanorods possess excellent catalytic activity for the Br₂/Br^? electrochemical reaction to reduce the electrochemical polarization. Moreover, the 3D micro–nano hierarchical nanorod‐array alignment structure contributes to a high electrolyte penetration and a high ion‐transfer rate to reduce diffusion polarization. As a result, a zinc–bromine flow battery with the designed composite electrode can be operated at a current density of up to 160 mA cm^?2, which is the highest current density ever reported. These results exhibit a promising strategy to fabricate electrodes for ultrahigh‐power‐density bromine‐based flow batteries and accelerate the development of bromine‐based flow batteries.     

Single Ni Atoms and Clusters Embedded in N‐Doped Carbon “Tubes on Fibers” Matrix with Bifunctional Activity for Water Splitting at High Current Densities

Among the bifunctional catalysts for water splitting, recently emerged transition‐metal single‐atom catalysts are theoretically considered to possess high potential, while the experimental activity is not satisfactory yet. Herein, an exceptionally efficient trifunctional metal–nitrogen–carbon (M–N–C) catalyst electrode, composed of a hierarchical carbon matrix embedding isolated nickel atoms with nickel–iron (NiFe) clusters, is presented. 1D microfibers and nanotubes grow sequentially from 2D nanosheets as sacrificial templates via two stages of solution‐ and solid‐phase reactions to form a 1D hierarchy. Exceptionally efficient bifunctional activity with an overpotential of only 13 mV at 10 mA cm^?2 toward hydrogen evolution reaction (HER) and an overpotential of 210 mV at 30 mA cm^?2 toward oxygen evolution reaction (OER) is obtained, surpassing each monofunctional activity ever reported. More importantly, an overpotential of only 126 and 326 mV is required to drive 500 mA cm^?2 toward the HER and OER, respectively. For the first time, industrial‐scale water splitting with two bifunctional catalyst electrodes with a current density of 500 mA cm^?2 at a potential of 1.71 V is demonstrated. Lastly, trifunctional catalytic activity including oxygen reduction reaction is also proven with a half‐wave potential at 0.848 V.     

Three‐Dimensional Self‐Supported Metal Oxides for Advanced Energy Storage

The miniaturization of power sources aimed at integration into micro‐ and nano‐electronic devices is a big challenge. To ensure the future development of fully autonomous on‐board systems, electrodes based on self‐supported 3D nanostructured metal oxides have become increasingly important, and their impact is particularly significant when considering the miniaturization of energy storage systems. This review describes recent advances in the development of self‐supported 3D nanostructured metal oxides as electrodes for innovative power sources, particularly Li‐ion batteries and electrochemical supercapacitors. Current strategies for the design and morphology control of self‐supported electrodes fabricated using template, lithography, anodization and self‐organized solution techniques are outlined along with different efforts to improve the storage capacity, rate capability, and cyclability.     

Highly Efficient (>10%) Flexible Organic Solar Cells on PEDOT‐Free and ITO‐Free Transparent Electrodes

A novel approach to fabricate flexible organic solar cells is proposed without indium tin oxide (ITO) and poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) using junction‐free metal nanonetworks (NNs) as transparent electrodes. The metal NNs are monolithically etched using nanoscale shadow masks, and they exhibit excellent optoelectronic performance. Furthermore, the optoelectrical properties of the NNs can be controlled by both the initial metal layer thickness and NN density. Hence, with an extremely thin silver layer, the appropriate density control of the networks can lead to high transmittance and low sheet resistance. Such NNs can be utilized for thin‐film devices without planarization by conductive materials such as PEDOT:PSS. A highly efficient flexible organic solar cell with a power conversion efficiency (PCE) of 10.6% and high device yield (93.8%) is fabricated on PEDOT‐free and ITO‐free transparent electrodes. Furthermore, the flexible solar cell retains 94.3% of the initial PCE even after 3000 bending stress tests (strain: 3.13%).     

Beyond Gold: Spin‐Coated Ti3C2‐Based MXene Photodetectors

2D transition metal carbides, known as MXenes, are transparent when the samples are thin enough. They are also excellent electrical conductors with metal‐like carrier concentrations. Herein, these characteristics are exploited to replace gold (Au) in GaAs photodetectors. By simply spin‐coating transparent Ti₃C₂‐based MXene electrodes from aqueous suspensions onto GaAs patterned with a photoresist and lifted off with acetone, photodetectors that outperform more standard Au electrodes are fabricated. Both the Au‐ and MXene‐based devices show rectifying contacts with comparable Schottky barrier heights and internal electric fields. The latter, however, exhibit significantly higher responsivities and quantum efficiencies, with similar dark currents, hence showing better dynamic range and detectivity, and similar sub‐nanosecond response speeds compared to the Au‐based devices. The simple fabrication process is readily integratable into microelectronic, photonic‐integrated circuits and silicon photonics processes, with a wide range of applications from optical sensing to light detection and ranging and telecommunications.     

Silver‐Quantum‐Dot‐Modified MoO3 and MnO2 Paper‐Like Freestanding Films for Flexible Solid‐State Asymmetric Supercapacitors

Free‐standing paper‐like thin‐film electrodes have great potential to boost next‐generation power sources with highly flexible, ultrathin, and lightweight requirements. In this work, silver‐quantum‐dot‐ (2–5 nm) modified transition metal oxide (including MoO₃ and MnO₂) paper‐like electrodes are developed for energy storage applications. Benefitting from the ohmic contact at the interfaces between silver quantum dots and MoO₃ nanobelts (or MnO₂ nanowires) and the binder‐free nature and 0D/1D/2D nanostructured 3D network of the fabricated electrodes, substantial improvements on the electrical conductivity, efficient ionic diffusion, and areal capacitances of the hybrid nanostructure electrodes are observed. With this proposed strategy, the constructed asymmetric supercapacitors, with Ag quantum dots/MoO₃ “paper” as anode, Ag quantum dots/MnO₂ “paper” as cathode, and neutral Na₂SO₄/polyvinyl alcohol hydrogel as electrolyte, exhibit significantly enhanced energy and power densities in comparison with those of the supercapacitors without modification of Ag quantum dots on electrodes; present excellent cycling stability at different current densities and good flexibility under various bending states; offer possibilities as high‐performance power sources with low cost, high safety, and environmental friendly properties.     

Coupling PEDOT on Mesoporous Vanadium Nitride Arrays for Advanced Flexible All‐Solid‐State Supercapacitors

Tailored construction of advanced flexible supercapacitors (SCs) is of great importance to the development of high‐performance wearable modern electronics. Herein, a facile combined wet chemical method to fabricate novel mesoporous vanadium nitride (VN) composite arrays coupled with poly(3,4‐ethylenedioxythiophene) (PEDOT) as flexible electrodes for all‐solid‐state SCs is reported. The mesoporous VN nanosheets arrays prepared by the hydrothermal–nitridation method are composed of cross‐linked nanoparticles of 10–50 nm. To enhance electrochemical stability, the VN is further coupled with electrodeposited PEDOT shell to form high‐quality VN/PEDOT flexible arrays. Benefiting from high intrinsic reactivity and enhanced structural stability, the designed VN/PEDOT flexible arrays exhibit a high specific capacitance of 226.2 F g^?1 at 1 A g^?1 and an excellent cycle stability with 91.5% capacity retention after 5000 cycles at 10 A g^?1. In addition, high energy/power density (48.36 Wh kg^?1 at 2 A g^?1 and 4 kW kg^?1 at 5 A g^?1) and notable cycling life (91.6% retention over 10 000 cycles) are also achieved in the assembled asymmetric flexible supercapacitor cell with commercial nickel–cobalt–aluminum ternary oxides cathode and VN/PEDOT anode. This research opens up a way for construction of advanced hybrid organic–inorganic electrodes for flexible energy storage.     

Coaggregation of κ‐Casein and β‐Lactoglobulin Produces Morphologically Distinct Amyloid Fibrils

The unfolding, misfolding, and aggregation of proteins lead to a variety of structural species. One form is the amyloid fibril, a highly aligned, stable, nanofibrillar structure composed of β‐sheets running perpendicular to the fibril axis. β‐Lactoglobulin (β‐Lg) and κ‐casein (κ‐CN) are two milk proteins that not only individually form amyloid fibrillar aggregates, but can also coaggregate under environmental stress conditions such as elevated temperature. The aggregation between β‐Lg and κ‐CN is proposed to proceed via disulfide bond formation leading to amorphous aggregates, although the exact mechanism is not known. Herein, using a range of biophysical techniques, it is shown that β‐Lg and κ‐CN coaggregate to form morphologically distinct co‐amyloid fibrillar structures, a phenomenon previously limited to protein isoforms from different species or different peptide sequences from an individual protein. A new mechanism of aggregation is proposed whereby β‐Lg and κ‐CN not only form disulfide‐linked aggregates, but also amyloid fibrillar coaggregates. The coaggregation of two structurally unrelated proteins into cofibrils suggests that the mechanism can be a generic feature of protein aggregation as long as the prerequisites for sequence similarity are met.     

Co@Co3O4 Core–Shell Three‐Dimensional Nano‐Network for High‐Performance Electrochemical Energy Storage

An alternative routine is presented by constructing a novel architecture, conductive metal/transition oxide (Co@Co₃O₄) core–shell three‐dimensional nano‐network (3DN) by surface oxidating Co 3DN in situ, for high‐performance electrochemical capacitors. It is found that the Co@Co₃O₄ core–shell 3DN consists of petal‐like nanosheets with thickness of <10 nm interconnected forming a 3D porous nanostructure, which preserves the original morphology of Co 3DN well. X‐ray photoelectron spectroscopy by polishing the specimen layer by layer reveals that the Co@Co₃O₄ nano‐network is core–shell‐like structure. In the application of electrochemical capacitors, the electrodes exhibit a high specific capacitance of 1049 F g^?1 at scan rate of 2 mV/s with capacitance retention of ～52.05% (546 F g^?1 at scan rate of 100 mV) and relative high areal mass density of 850 F g^?1 at areal mass of 3.52 mg/cm². It is believed that the good electrochemical behaviors mainly originate from its extremely high specific surface area and underneath core‐Co “conductive network”. The high specific surface area enables more electroactive sites for efficient Faradaic redox reactions and thus enhances ion and electron diffusion. The underneath core‐Co “conductive network” enables an ultrafast electron transport.     

Roll‐to‐Roll Production of Graphene Hybrid Electrodes for High‐Efficiency,Flexible Organic Photoelectronics

Despite nearly two decades of research, the absence of ideal, flexible, and transparent electrodes has been the biggest bottleneck for realizing flexible and printable electronics via roll‐to‐roll (R2R) method. A fabrication of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate):graphene:ethyl cellulose (PEDOT:PSS:G:EC) hybrid electrodes by R2R process, which allows for the elimination of strong acid treatment. The high‐performance flexible printable electrode includes a transmittance (T) of 78% at 550 nm and a sheet resistance of 13 Ω sq⁻¹ with excellent mechanical stability. These features arise from the PSS interacting strongly with the ethyoxyl groups from EC promoting a favorable phase separation between PEDOT and PSS chains, and the highly uniform and conductive G:EC enable rearrangement of the PEDOT chains with more expanded conformation surrounded by G:EC via the π–π interaction between G:EC and PEDOT. The hybrid electrodes are fully functional as universal electrodes for outstanding flexible electronic applications. Organic solar cells based on the hybrid electrode exhibit a high power conversion efficiency of 9.4% with good universality for active layer. Moreover, the organic light‐emitting diodes and photodetector devices hold the same level to or outperform those based on indium tin oxide flexible transparent electrodes.     

Mineral‐Templated 3D Graphene Architectures for Energy‐Efficient Electrodes

3D graphene networks have shown extraordinary promise for high‐performance electrochemical devices. Herein, the chemical vapor deposition synthesis of a highly porous 3D graphene foam (3D‐GF) using naturally abundant calcined Iceland crystal as the template is reported. Intriguingly, the Iceland crystal transforms to CaO monolith with evenly distributed micro/meso/macropores through the releasing of CO₂ at high temperature. Meanwhile, the hierarchical structure of the calcined template could be easily tuned under different calcination conditions. By precisely inheriting fine structure from the templates, the as‐prepared 3D‐GF possesses a tunable hierarchical porosity and low density. Thus, the hierarchical pores offer space for guest hybridization and provide an efficient pathway for ion/charge transport in typical energy conversion/storage systems. The 3D‐GF skeleton electrode hybridized with Ni(OH)₂/Co(OH)₂ through an optimal electrodeposition condition exhibits a high specific capacitance of 2922.2 F g⁻¹ at a scan rate of 10 mV s⁻¹, and 2138.4 F g⁻¹ at a discharge current density of 3.1 A g⁻¹. The hybrid 3D‐GF symmetry supercapacitor shows a high energy density of 83.0 Wh kg⁻¹ at a power density of 1011.3 W kg⁻¹ and 31.4 Wh kg⁻¹ at a high power density of 18 845.2 W kg⁻¹. The facile fabrication process enables the mass production of hierarchical porous 3D‐GF for high‐performance supercapacitors.     

3‐D Integrated All‐Solid‐State Rechargeable Batteries

Portable society urgently calls for integrated energy supplies. This holds for autonomous devices but even more so for future medical implants. Evidently, rechargeable integrated all‐solid‐state batteries will play a key role in these fields, enabling miniaturization, preventing electrode degradation upon cycling and electrolyte leakage. Planar solid‐state thin film batteries are rapidly emerging but reveal several potential drawbacks, such as a relatively low energy density and the use of highly reactive lithium. Thin film Si‐intercalation electrodes covered with a solid‐state electrolyte are found to combine a high storage capacity of 3500 mAh g^–1 with high cycle life, enabling to integrate batteries in Si. Based on the excellent intercalation chemistry of Si, a new 3D‐integrated all‐solid‐state battery concept is proposed. High aspect ratio cavities and features, etched in silicon, will yield large surface area batteries with anticipated energy density of about 5 mWh μm^–1 cm^–2, i.e. more than 3 orders of magnitude higher than that of integrated capacitors.     

Creating Graphitic Carbon Nitride Based Donor‐π–Acceptor‐π–Donor Structured Catalysts for Highly Photocatalytic Hydrogen Evolution

Conjugated polymers with tailored donor–acceptor units have recently attracted considerable attention in organic photovoltaic devices due to the controlled optical bandgap and retained favorable separation of charge carriers. Inspired by these advantages, an effective strategy is presented to solve the main obstructions of graphitic carbon nitride (g‐C₃N₄) photocatalyst for solar energy conversion, that is, inefficient visible light response and insufficient separation of photogenerated electrons and holes. Donor‐π–acceptor‐π–donor polymers are prepared by incorporating 4,4′‐(benzoc 1,2,5 thiadiazole‐4,7‐diyl) dianiline (BD) into the g‐C₃N₄ framework (UCN‐BD). Benefiting from the visible light band tail caused by the extended π conjugation, UCN‐BD possesses expanded visible light absorption range. More importantly, the BD monomer also acts as an electron acceptor, which endows UCN‐BD with a high degree of intramolecular charge transfer. With this unique molecular structure, the optimized UCN‐BD sample exhibits a superior performance for photocatalytic hydrogen evolution upon visible light illumination (3428 µmol h^?1 g^?1), which is nearly six times of that of the pristine g‐C₃N₄. In addition, the photocatalytic property remains stable for six cycles in 3 d. This work provides an insight into the synthesis of g‐C₃N₄‐based D‐π–A‐π–D systems with highly visible light response and long lifetime of intramolecular charge carriers for solar fuel production.     

Novel 3D Wollastonite‐Based Scaffolds from Preceramic Polymers Containing Micro‐ and Nano‐Sized Reactive Particles

Wollastonite (CaSiO₃) ceramics are well known biomaterials which can be produced using many different techniques. The present paper illustrates an innovative processing method employing preceramic polymers (silicone resins) containing CaCO₃ micro‐ and nano‐sized particles, which act as reactive fillers. Silica from the decomposition of the silicone resins reacts at low temperature with the CaO deriving from the fillers, yielding wollastonite ceramics. Hydroxyapatite powders can also be added, to modify the biological response of the material. This approach enables the fabrication of 3D scaffolds via fused deposition or via conventional hot extrusion.     

Foldable Electrode Architectures Based on Silver‐Nanowire‐Wound or Carbon‐Nanotube‐Webbed Micrometer‐Scale Fibers of Polyethylene Terephthalate Mats for Flexible Lithium‐Ion Batteries

A crumply and highly flexible lithium‐ion battery is realized by using microfiber mat electrodes in which the microfibers are wound or webbed with conductive nanowires. This electrode architecture guarantees extraordinary mechanical durability without any increase in resistance after folding 1000 times. Its areal energy density is easily controllable by the number of folded stacks of a piece of the electrode mat. Deformable lithium‐ion batteries of lithium iron phosphate as cathode and lithium titanium oxide as anode at high areal capacity (3.2 mAh cm^?2) are successfully operated without structural failure and performance loss, even after repeated crumpling and folding during charging and discharging.     

Hierarchical 3D All‐Carbon Composite Structure Modified with N‐Doped Graphene Quantum Dots for High‐Performance Flexible Supercapacitors

Flexible supercapacitors have shown enormous potential for portable electronic devices. Herein, hierarchical 3D all‐carbon electrode materials are prepared by assembling N‐doped graphene quantum dots (N‐GQDs) on carbonized MOF materials (cZIF‐8) interweaved with carbon nanotubes (CNTs) for flexible all‐solid‐state supercapacitors. In this ternary electrode, cZIF‐8 provides a large accessible surface area, CNTs act as the electrical conductive network, and N‐GQDs serve as highly pseudocapactive materials. Due to the synergistic effect and hierarchical assembly of these components, N‐GQD@cZIF‐8/CNT electrodes exhibit a high specific capacitance of 540 F g^?1 at 0.5 A g^?1 in a 1 m H₂SO₄ electrolyte and excellent cycle stability with 90.9% capacity retention over 8000 cycles. The assembled supercapacitor possesses an energy density of 18.75 Wh kg^?1 with a power density of 108.7 W kg^?1. Meanwhile, three supercapacitors connected in series can power light‐emitting diodes for 20 min. All‐solid‐state N‐GQD@cZIF‐8/CNT flexible supercapacitor exhibits an energy density of 14 Wh kg^?1 with a power density of 89.3 W kg^?1, while the capacitance retention after 5000 cycles reaches 82%. This work provides an effective way to construct novel electrode materials with high energy storage density as well as good cycling performance and power density for high‐performance energy storage devices via the rational design.     

Control of thermoelectric properties in ZrO2/CoSb3 nano‐dispersed composites

Nano‐dispersed ZrO₂/CoSb₃ composites of various composition were prepared by uniaxial hot pressing of nano‐sized powders of thermoelectric CoSb₃ intermixed with ceramic nano‐powders. The phase purity, the microstructure, and the temperature dependent transport parameters of the composites were investigated. Non‐dispersed samples from nano‐sized CoSb₃ powders show higher electrical conductivity compared to melt‐grown material which is attributed to the presence of a small excess of metallic Sb, but they exhibit lower thermal conductivity due to the fine‐grained structure. Addition of 5 at.‐% ZrO₂ enhances the ratio of electrical to thermal conductivity, whereas hardly affects the Seebeck coefficient. In this manner the nano‐dispersion method provides an effective approach to improving the material´s thermoelectric performance.     

Wafer‐Scale Patterning of Reduced Graphene Oxide Electrodes by Transfer‐and‐Reverse Stamping for High Performance OFETs

A wafer‐scale patterning method for solution‐processed graphene electrodes, named the transfer‐and‐reverse stamping method, is universally applicable for fabricating source/drain electrodes of n‐ and p‐type organic field‐effect transistors with excellent performance. The patterning method begins with transferring a highly uniform reduced graphene oxide thin film, which is pre‐prepared on a glass substrate, onto hydrophobic silanized (rigid/flexible) substrates. Patterns of the as‐prepared reduced graphene oxide films are then formed by modulating the surface energy of the films and selectively delaminating the films using an oxygen‐plasma‐treated elastomeric stamp with patterns. Reduced graphene oxide patterns with various sizes and shapes can be readily formed onto an entire wafer. Also, they can serve as the source/drain electrodes for benchmark n‐ and p‐type organic field‐effect transistors with enhanced performance, compared to those using conventional metal electrodes. These results demonstrate the general utility of this technique. Furthermore, this simple, inexpensive, and scalable electrode‐patterning‐technique leads to assembling organic complementary circuits onto a flexible substrate successfully.     

High‐Entropy Alloy (HEA)‐Coated Nanolattice Structures and Their Mechanical Properties

Nanolattice structure fabricated by two‐photon lithography (TPL) is a coupling of size‐dependent mechanical properties at micro/nano‐scale with structural geometry responses in wide applications of scalable micro/nano‐manufacturing. In this work, three‐dimensional (3D) polymeric nanolattices are initially fabricated using TPL, then conformably coated with an 80 nm thick high‐entropy alloy (HEA) thin film (CoCrFeNiAl_0.3) via physical vapor deposition (PVD). 3D atomic‐probe tomography (APT) reveals the homogeneous element distribution in the synthesized HEA film deposited on the substrate. Mechanical properties of the obtained composite architectures are investigated via in situ scanning electron microscope (SEM) compression test, as well as finite element method (FEM) at the relevant length scales. The presented HEA‐coated nanolattice encouragingly not only exhibits superior compressive specific strength of ≈0.032 MPa kg^?1 m³ with density well below 1000 kg m^?3, but also shows good compression ductility due to its composite nature. This concept of combining HEA with polymer lattice structures demonstrates the potential of fabricating novel architected metamaterials with tunable mechanical properties.