Drying-Mediated Self-Assembly of Graphene for Inkjet Printing of High-Rate Micro-supercapacitors

3D Printing of Hierarchical Structures Made of Inorganic Silicon-Rich Glass Featuring Self-Forming Nanogratings

Hierarchical structures are abundant in nature, such as in the superhydrophobic surfaces of lotus leaves and the structural coloration of butterfly wings. They consist of ordered features across multiple size scales, and their advantageous properties have attracted enormous interest in wide-ranging fields including energy storage, nanofluidics, and nanophotonics. Femtosecond lasers, which are capable of inducing various material modifications, have shown promise for manufacturing tailored hierarchical structures. However, existing methods, such as multiphoton lithography and three-dimensional (3D) printing using nanoparticle-filled inks, typically involve polymers and suffer from high process complexity. Here, we demonstrate the 3D printing of hierarchical structures in inorganic silicon-rich glass featuring self-forming nanogratings. This approach takes advantage of our finding that femtosecond laser pulses can induce simultaneous multiphoton cross-linking and self-formation of nanogratings in hydrogen silsesquioxane. The 3D printing process combines the 3D patterning capability of multiphoton lithography and the efficient generation of periodic structures by the self-formation of nanogratings. We 3D-printed micro-supercapacitors with large surface areas and a high areal capacitance of 1 mF/cm2 at an ultrahigh scan rate of 50 V/s, thereby demonstrating the utility of our 3D printing approach for device applications in emerging fields such as energy storage.

Bioinspired Synaptic Branched Network within Quasi-Solid Polymer Electrolyte for High-Performance Microsupercapacitors

The branched network-driven ion solvating quasi-solid polymer electrolytes (QSPEs) are prepared via one-step photochemical reaction. A poly(ethylene glycol diacrylate) (PEGDA) is combined with an ion-conducting solvate ionic liquid (SIL), where tetraglyme (TEGDME), which acts like interneuron in the human brain and creates branching network points, is mixed with EMIM-NTf2 and Li-NTf2. The QSPE exhibits a unique gyrified morphology, inspired by the cortical surface of human brain, and features well-refined nano-scale ion channels. This human-mimicking method offers excellent ion transport capabilities through a synaptic branched network with high ionic conductivity (σDC ≈ 1.8 mS cm-1 at 298 K), high dielectric constant (εs ≈ 125 at 298 K), and strong ion solvation ability, in addition to superior mechanical flexibility. Furthermore, the interdigitated microsupercapacitors (MSCs) based on the QSPE present excellent electrochemical performance of high energy (E  =  5.37 µWh cm-2) and power density (P  =  2.2 mW cm-2), long-term cycle stability (≈94% retention after 48 000 cycles), and mechanical stability (>94% retention after continuous bending and compressing deformation). Moreover, these MSC devices have flame-retarding properties and operate effectively in air and water across a wide temperature range (275 to 370 K), offering a promising foundation for high-performance, stable next-generation all-solid-state energy storage devices.

Ultrafast Metal-Free Microsupercapacitor Arrays Directly Store Instantaneous High-Voltage Electricity from Mechanical Energy Harvesters

Harvesting renewable mechanical energy is envisioned as a promising and sustainable way for power generation. Many recent mechanical energy harvesters are able to produce instantaneous (pulsed) electricity with a high peak voltage of over 100 V. However, directly storing such irregular high-voltage pulse electricity remains a great challenge. The use of extra power management components can boost storage efficiency but increase system complexity. Here utilizing the conducting polymer PEDOT:PSS, high-rate metal-free micro-supercapacitor (MSC) arrays are successfully fabricated for direct high-efficiency storage of high-voltage pulse electricity. Within an area of 2.4 × 3.4 cm2 on various paper substrates, large-scale MSC arrays (comprising up to 100 cells) can be printed to deliver a working voltage window of 160 V at an ultrahigh scan rate up to 30 V s-1. The ultrahigh rate capability enables the MSC arrays to quickly capture and efficiently store the high-voltage (≈150 V) pulse electricity produced by a droplet-based electricity generator at a high efficiency of 62%, significantly higher than that (<2%) of the batteries or capacitors demonstrated in the literature. Moreover, the compact and metal-free features make these MSC arrays excellent candidates for sustainable high-performance energy storage in self-charging power systems.

Insights into Nano- and Micro-Structured Scaffolds for Advanced Electrochemical Energy Storage

Adopting a nano- and micro-structuring approach to fully unleashing the genuine potential of electrode active material benefits in-depth understandings and research progress toward higher energy density electrochemical energy storage devices at all technology readiness levels. Due to various challenging issues, especially limited stability, nano- and micro-structured (NMS) electrodes undergo fast electrochemical performance degradation. The emerging NMS scaffold design is a pivotal aspect of many electrodes as it endows them with both robustness and electrochemical performance enhancement, even though it only occupies complementary and facilitating components for the main mechanism. However, extensive efforts are urgently needed toward optimizing the stereoscopic geometrical design of NMS scaffolds to minimize the volume ratio and maximize their functionality to fulfill the ever-increasing dependency and desire for energy power source supplies. This review will aim at highlighting these NMS scaffold design strategies, summarizing their corresponding strengths and challenges, and thereby outlining the potential solutions to resolve these challenges, design principles, and key perspectives for future research in this field. Therefore, this review will be one of the earliest reviews from this viewpoint.

Recent progress in electrode materials for micro-supercapacitors

Micro-supercapacitors (MSCs) stand out in the field of micro energy storage devices due to their high power density, long cycle life, and environmental friendliness. The key to improving the electrochemical performance of MSCs is the selection of appropriate electrode materials. To date, both the composition and structure of electrode materials in MSCs have become a hot research topic, and it is urgent to compose a review to highlight the most important research achievements, major challenges, opportunities, and encouraging perspectives in this field. In this review, research background of MSCs is first reviewed followed by their working principles, structural classifications, and physiochemical and electrochemical characterization techniques. Next, various materials and preparation methods are summarized, and the relationship between the MSC performance and structure and composition of materials are discussed in depth. Finally, this review provides a comprehensive suggestion on accelerating the development of electrode materials to facilitate the commercialization of MSCs.

Co3 O4 Quantum Dots Intercalation Liquid-Crystal Ordered-Layered-Structure Optimizing the Performance of 3D-Printing Micro-Supercapacitors

The effects of near surface or surface mechanisms on electrochemical performance (lower specific capacitance density) hinders the development of 3D printed micro supercapacitors (MSCs). The reasonable internal structural characteristics of printed electrodes and the appropriate intercalation material can effectively compensate for the effects of surface or near-surface mechanisms. In this study, a layered structure is constructed inside an electrode using an ink with liquid-crystal characteristics, and the pore structure and oxidation active sites of the layered electrode are optimized by controlling the amount of Co3 O4 -quantum dots (Co3 O4 QDs). The Co3 O4 QDs are distributed in the pores of the electrode surface, and the insertion of Co3 O4 QDs can effectively compensate for the limitations of surface or near-surface mechanisms, thus effectively improving the pseudocapacitive characteristics of the 3D-printed MSCs. The 3D printed MSC exhibits a high area capacitance (306.13 mF cm-2 ) and energy density (34.44 µWh cm-2 at a power density of 0.108 mW cm-2 ). Therefore, selecting the appropriate materials to construct printable electrode structures and effectively adjusting material ratios for efficient 3D printing are expected to provide feasible solutions for the construction of various high-energy storage systems such as MSCs.

Ethanol-Induced Ni2+ -Intercalated Cobalt Organic Frameworks on Vanadium Pentoxide for Synergistically Enhancing the Performance of 3D-Printed Micro-Supercapacitors

The synthesis of metal-organic framework (MOF) nanocomposites with high energy density and excellent mechanical strength is limited by the degree of lattice matching and crystal surface structure. In this study, dodecahedral ZIF-67 is synthesized uniformly on vanadium pentoxide nanowires. The influence of the coordination mode on the surface of ZIF-67 in ethanol is also investigated. Benefitting from the different coordination abilities of Ni²⁺ , Co²⁺ , and N atoms, spatially separated surface-active sites are created through metal-ion exchange. Furthermore, the incompatibility between the d⁸ electronic configuration of Ni²⁺ and the three-dimensional (3D) structure of ZIF-67 afforded the synthesis of hollow structures by controlling the amount of Ni doping. The formation of NiCo-MOF@CoOOH@V₂ O₅ nanocomposites is confirmed using X-ray absorption fine structure analysis. The high performance of the obtained composite is illustrated by fabricating a 3D-printed micro-supercapacitor, exhibiting a high area specific capacitance of 585 mF cm^-2 and energy density of 159.23 µWh cm^-2 (at power density = 0.34 mW cm^-2 ). The solvent/coordination tuning strategy demonstrated in this study provides a new direction for the synthesis of high-performance nanomaterials for electrochemical energy storage applications.

Ordered stripes to crack patterns in dried particulates of DNA-coated gold colloids via modulating nanoparticle-substrate interactions

The surface pattern in dried droplets of nanoparticle suspension possesses direct correlation with the evaporation profile, which apart from the bulk parameters, can also be altered by tuning the nanoscale interactions. Here, we show that, for sessile drops of DNA-coated gold nanoparticle (DNA-AuNP) solution, the alteration in evaporation pathway of TPCL (three-phase contact line) from stick-slip to mixed mode leads to a surface morphological transition from concentric rings with stripes to radial crack formation within the coffee ring deposit. A freshly cleaned silicon substrate offers hydrophilic/favorable substrate-nanoparticle interaction and produces multiple ordered stripes due to stick-slip motion of the TPCL. Using a SiO₂/Si substrate with ∼200 nm of oxide layer leads to an increase in the initial water contact angle θ_i-w by ∼40°, due to increased hydrophobicity of the substrate. Three distinct modes of evaporation are observed - constant contact radius (CCR), constant contact angle (CCA) and mixed mode, resulting in the formation of radial cracks on a thick coffee ring structure. The critical thickness (h_c), beyond which the cracks start to appear, was measured to be ∼600 nm and is in close agreement with the theoretical estimate of ∼510 nm. Through in situ contact angle and ex situ SEM measurements, we provide an understanding of the observed surface morphological transition in the dried particulate at various nanoparticle densities. Further analysis of the coffee ring width (d), linear crack density (σ) and crack spacing (λ) provides insight into the mechanism of crack formation for droplets dried on oxide-coated substrates.

Pushing the Electrochemical Performance Limits of Polypyrrole Toward Stable Microelectronic Devices

Conducting polymers have achieved remarkable attentions owing to their exclusive characteristics, for instance, electrical conductivity, high ionic conductivity, visual transparency, and mechanical tractability. Surface and nanostructure engineering of conjugated conducting polymers offers an exceptional pathway to facilitate their implementation in a variety of scientific claims, comprising energy storage and production devices, flexible and wearable optoelectronic devices. A two-step tactic to assemble high-performance polypyrrole (PPy)-based microsupercapacitor (MSC) is utilized by transforming the current collectors to suppress structural pulverization and increase the adhesion of PPy, and then electrochemical co-deposition of PPy-CNT nanostructures on rGO@Au current collectors is performed. The resulting fine patterned MSC conveyed a high areal capacitance of 65.9 mF cm-2 (at a current density of 0.1 mA cm-2), an exceptional cycling performance of retaining 79% capacitance after 10,000 charge/discharge cycles at 5 mA cm-2. Benefiting from the intermediate graphene, current collector free PPy-CNT@rGO flexible MSC is produced by a facile transfer method on a flexible substrate, which delivered an areal capacitance of 70.25 mF cm-2 at 0.1 mA cm-2 and retained 46% of the initial capacitance at a current density of 1.0 mA cm-2. The flexible MSC is utilized as a skin compatible capacitive micro-strain sensor with excellent electromechanochemical characteristics.

Effect of Surface Treatment on Performance and Internal Stacking Mode of Electrohydrodynamic Printed Graphene and Its Microsupercapacitor

Microelectronic devices are developing rapidly in portability, wearability, and implantability. This puts forward an urgent requirement for the delicate deposition process of materials. Electrohydrodynamic printing has attracted academic and industrial attention in preparing ultrahigh-density microelectronic devices as a new noncontact, direct graphic, and low-loss thin film deposition process. In this work, a printed graphene with narrow line width is realized by combining the electrohydrodynamic printing and surface treatment. The line width of printed graphene on the hydrophobic treatment surface reduced from 80 to 28 μm. The resistivity decreased from 0.949 to 0.263 Ω·mm. Unexpectedly, hydrophobic treatment can effectively induce random stacking of electrohydrodynamic printed graphene, which avoids parallel stacking and agglomeration of graphene sheets. The performance of printed graphene is thus effectively improved. After optimization, a graphene planar supercapacitor with a printed line width of 28 μm is successfully obtained. Its capacitance can reach 5.39 mF/cm² at 50 mV/s, which is twice higher than that of the untreated devices. The device maintains 84.7% capacitance after 5000 cycles. This work provides a reference for preparing microelectronic devices by ultrahigh precision printing and a new direction for optimizing two-dimensional material properties through stacking adjustment.

Engineering Interlaced Architecture of Pristine Graphene Anchored with 2-Amino-8-Naphthol 6-Sulfonic Acids for Printed Hybrid Micro-Supercapacitors with High Electrochemical Capability

All-printed flexible micro-supercapacitors (MSCs) based on two-dimensional (2D) nanomaterials with in-plane interdigital configurations are regarded as promising miniaturized power source units, but they chronically suffer from self-aggregation and inadequate matching of electrode materials, thus resulting in inefficient electrolyte ions intercalation. Herein, an innovative multicomponent interlaced architecture essentially consisting of 2-amino-8-naphthol 6-sulfonic acid (ANS)-anchored pristine graphene and highly conductive multiwalled carbon nanotubes is reported. The assembled and optimized Gr@ANS electrodes offer sufficient absorption/desorption and redox-active sites, delivering a high areal capacitance of 33.7 mF/cm² for screen-printed MSCs. Particularly, the well-modified Gr@ANS/CNTs-interlaced complex structure effectively prevents the usual restacking of the delaminated Gr@ANS nanosheets and maximizes ion accessibility in electrodes. Ascribed to the optimized electron-transferring kinetics, the achieved Gr@ANS/CNTs MSCs exhibit excellent capacitance (40.2 mF/cm² and 18.8 F/cm³), simultaneously significantly increasing the rate capability of Gr@ANS MSCs (from 3.9 to 60.0%). Arising from the multicomponent synergism, the all-solid-state MSCs exhibit outstanding bending stability and cycling performance (73.8% after 10 000 charge/discharge cycles). The new charge reservoir engineering evidenced in graphene-based micro-supercapacitors would serve as a stepping stone toward the scalable manufacture of hybrid energy storage micro-devices.

SLM-processed MoS2/Mo2S3 nanocomposite for energy conversion/storage applications

MoS₂-based nanocomposites have been widely processed by a variety of conventional and 3D printing techniques. In this study, selective laser melting (SLM) has for the first time successfully been employed to tune the crystallographic structure of bulk MoS₂ to a 2H/1T phase and to distribute Mo₂S₃ nanoparticles in-situ in MoS₂/Mo₂S₃ nanocomposites used in electrochemical energy conversion/storage systems (EECSS). The remarkable results promote further research on and elucidate the applicability of laser-based powder bed processing of 2D nanomaterials for a wide range of functional structures within, e.g., EECSS, aerospace, and possibly high-temperature solid-state EECSS even in space.

Ocean wave energy generator based on graphene/TiO2 nanoparticle composite films

Harvesting ocean wave energy through carbon-based materials, particularly graphene, is receiving increasing attention. However, the complicated fabrication process and the low output power of the present monolayer graphene-based wave energy generators limit their further application. Here, we demonstrate the facile fabrication of a new type of wave energy generator based on graphene/TiO₂ nanoparticle composite films using the doctor-blading method. The developed wave energy harvesting device exhibits a high open-circuit voltage of up to 75 millivolts and a high output power up to 1.8 microwatts. A systematic study was conducted to explore the optimal conditions for the energy harvesting performance.

A Universal Ternary-Solvent-Ink Strategy toward Efficient Inkjet-Printed Perovskite Quantum Dot Light-Emitting Diodes

Toward next-generation electroluminescent quantum dot (QD) displays, inkjet printing technique has been convinced as one of the most promising low-cost and large-scale manufacturing of patterned quantum dot light-emitting diodes (QLEDs). The development of high-quality and stable QD inks is a key step to push this technology toward practical applications. Herein, a universal ternary-solvent-ink strategy is proposed for the cesium lead halides (CsPbX₃ ) perovskite QDs and their corresponding inkjet-printed QLEDs. With this tailor-made ternary halogen-free solvent (naphthene, n-tridecane, and n-nonane) recipe, a highly dispersive and stable CsPbX₃ QD ink is obtained, which exhibits much better printability and film-forming ability than that of the binary solvent (naphthene and n-tridecane) system, leading to a much better qualitied perovskite QD thin film. Consequently, a record peak external quantum efficiency (EQE) of 8.54% and maximum luminance of 43 883.39 cd m^-2 is achieved in inkjet-printed green perovskite QLEDs, which is much higher than that of the binary-solvent-system-based devices (EQE = 2.26%). Moreover, the ternary-solvent-system exhibits a universal applicability in the inkjet-printed red and blue perovskite QLEDs as well as cadmium (Cd)-based QLEDs. This work demonstrates a new strategy for tailor-making a general ternary-solvent-QD-ink system for efficient inkjet-printed QLEDs as well as the other solution-processed electronic devices in the future.

Recent progress in acoustic field-assisted 3D-printing of functional composite materials

Acoustic forces are an attractive pathway to achieve directed assembly for multi-phase materials via additive processes. Programmatic integration of microstructure and structural features during deposition offers opportunities for optimizing printed component performance. We detail recent efforts to integrate acoustic focusing with a direct-ink-write mode of printing to modulate material transport properties (e.g. conductivity). Acoustic field-assisted printing, operating under a multi-node focusing condition, supports deposition of materials with multiple focused lines in a single-pass printed line. Here, we report the demonstration of acoustic focusing in concert with diffusive self-assembly to rapidly assembly and print multiscale, mm-length colloidal solids on a timescale of seconds to minutes. These efforts support the promising capabilities of acoustic field-assisted deposition-based printing to achieve spatial control of printed microstructures with deterministic, long-range ordering across multiple length scales.

Facile fabrication of graphene-based high-performance microsupercapacitors operating at a high temperature of 150 °C

Many industry applications require electronic circuits and systems to operate at high temperatures over 150 °C. Although planar microsupercapacitors (MSCs) have great potential for miniaturized on-chip integrated energy storage components, most of the present devices can only operate at low temperatures (<100 °C). In this work, we have demonstrated a facile process to fabricate activated graphene-based MSCs that can work at temperatures as high as 150 °C with high areal capacitance over 10 mF cm^-2 and good cycling performance. Remarkably, the devices exhibit no capacitance degradation during temperature cycling between 25 °C and 150 °C, thanks to the thermal stability of the active components.

Selective deposition of metal oxide nanoflakes on graphene electrodes to obtain high-performance asymmetric micro-supercapacitors

To meet the charging market demands of portable microelectronics, there has been a growing interest in high performance and low-cost microscale energy storage devices with excellent flexibility and cycling durability. Herein, interdigitated all-solid-state flexible asymmetric micro-supercapacitors (A-MSCs) were fabricated by a facile pulse current deposition (PCD) approach. Mesoporous Fe2O3 and MnO2 nanoflakes were functionally coated by electrodeposition on inkjet-printed graphene patterns as negative and positive electrodes, respectively. Our PCD approach shows significantly improved adhesion of nanostructured metal oxide with crack-free and homogeneous features, as compared with other reported electrodeposition approaches. The as-fabricated Fe2O3/MnO2 A-MSCs deliver a high volumetric capacitance of 110.6 F cm-3 at 5 μA cm-2 with a broad operation potential range of 1.6 V in neutral LiCl/PVA solid electrolyte. Furthermore, our A-MSC devices show a long cycle life with a high capacitance retention of 95.7% after 10 000 cycles at 100 μA cm-2. Considering its low cost and potential scalability to industrial levels, our PCD technique could be an efficient approach for the fabrication of high-performance MSC devices in the future.

Inkjet-Printing Technology for Supercapacitor Application: Current State and Perspectives

Inkjet-printing (IJP) technology is recognized as a significant breakthrough in manufacturing high-performance electrochemical energy storage systems. In comparison to conventional fabrication protocols, this printing technique offers various advantages, such as contact-less high-resolution patterning capability; low-cost, controlled material deposition; process simplicity; and compatibility with a variety of substrates. Due to these outstanding merits, significant research efforts have been devoted to utilizing IJP technology in developing electrochemical energy storage devices, particularly in supercapacitors (SCs). These attempts have focused on fabricating the key components of SCs, including electrode, electrolyte, and current collector, through rational formulation and patterning of functional inks. In an attempt to further expand the material design strategy and accelerate technology development, it is urgent and essential to obtain an in-depth insight into the recent developments of inkjet-printed SCs. Toward this aim, first, a general introduction to the fundamental principles of IJP technology is provided. After that, the latest achievements in IJP of capacitive energy storage devices are systematically summarized and discussed with a particular emphasis on the design of printable functional materials, the printing process, and capacitive performance of inkjet-printed SCs. To close, existing challenges and future research trends for developing state-of-the-art inkjet-printed SCs are proposed.