Sand-Milling Fabrication of Screen-Printable Graphene Composite Inks for High-Performance Planar Micro-Supercapacitors

Design of Porous 3D Interdigitated Current Collectors and Hybrid Microcathodes for Zn-Ion Microcapacitors

Zinc-ion microcapacitors (ZIMCs) have gained considerable attention for their intrinsic charge storage mechanisms, combining a battery-type anode with a capacitor-type cathode. However, their development is constrained by challenges related to electrode material selection and microscale device design, especially given the limited footprint of such devices. Despite their potential, exploration of smart electrode processing and hybrid materials for on-chip ZIMCs remains limited. In this work, we introduce 3D gold interdigitated electrodes (3D Au IDEs) as highly porous current collectors, loaded with zinc (Zn) as the anode and hybrid activated carbon coated with PEDOT (AC-PEDOT) as the cathode, using an advanced microplotter fabrication technique. Compared with planar Zn//AC ZIMCs, where Zn and AC materials are loaded onto planar Au IDEs, the 3D Au Zn//AC-PEDOT ZIMCs demonstrate significantly enhanced performance. This is attributed to the critical role of IDEs in increasing the charge storage capacity, improving long-term cycling stability, and boosting capacitive-controlled charge storage contributions. The 3D Au Zn//AC-PEDOT ZIMCs achieve an areal capacity of 1.3 μAh/cm2, peak areal energy of 1.11 μWh/cm2, and peak areal power of 640 μW/cm2, surpassing most reported microsupercapacitors. This study highlights how optimized collectors and hybrid electrodes enhance microdevice charge storage while maximizing performance within a constrained footprint.

Preparation and Characterization of Char Carbon Obtained by Carbonization of Unused Cigarette Filter Rods: The Product Application Assessment

The development of carbonaceous materials such as biochar has triggered a hot spot in materials application. In this study, a new type of char carbon was developed from raw cigarette filter rods (CFRs) via a carbonization process under moderate conditions (T = 550 °C; tres = 1 h) (CFR char carbon). The produced char was characterized by ATR-FTIR (Attenuated total reflectance-Fourier-transform infrared) spectroscopy, XRD (X-ray diffraction) analysis, GC-MS (Gas Chromatography-Mass Spectrometry), FESEM-EDS (Field-Emission Scanning Electron Microscopy-Energy-dispersive X-ray spectroscopy) technique, XPS (X-ray photoelectron spectroscopy), and N2 adsorption/desorption (BET) measurements. The obtained carbon material is rich in oxygen-containing functional groups (i.e., C=O, C-O, -C(=O)-CH3, C-O-C, C-OH, and O=C-O, with chemisorbed oxygen), containing significant amounts of calcium (that originates from CaCO3) and silicon (Si), generated by reduction of SiO2. It was found that the formation of char(C)/n-alkane composite material makes that CFR char have a high compressive strength improvement. Moderate carbonization has contributed to the creation of such material that has a fairly high specific surface area (320.93 m2/g), exhibiting a complex hierarchical structure that was characterized by composite Type I/IV(a) isotherm, associated with micro-/mesoporous carbon material. In addition, more directional extensions of this research for future work were proposed, including the implementation of electrochemical research.

Improving Electrochemical Performance in Planar On-Chip Zn-ion Micro-Batteries via Interlayer Strategies

The imperative development of planar on-chip micro-batteries featuring high-capacity electrodes and environmentally safer, cost-effective, and stable systems is crucial for powering forthcoming miniaturized systems-on-chip smart devices. However, research in the area of high-stability micro-batteries is limited due to the complex fabrication process, the stability of micro-electrodes during cycling, and the challenge of maintaining higher capacity within a limited device footprint. In response to this need, this study focuses on providing highly stable and high-capacity micro-electrodes. This involves adding a PEDOT layer between the electrode material and the current collector, applied within a planar polyaniline cathode and zinc anode device structure to enhance charge storage performance. This straightforward strategy not only improves device stability over long-term cycling and reduces charge transfer resistance but also increases charge storage capacities from 17.64 to 19.75 µAh cm- 2 at 0.1 mA cm- 2. Consequently, the Zn-ion micro-batteries achieve notable peak areal energy and power of 18.82 µWh cm- 2 and 4.37 mW cm- 2, respectively. This work proposes an effective strategy to enhance the electrochemical performance of planar micro-batteries, a critical advancement for the development of advanced portable electronics.

Advanced Porous Gold-PANI Micro-Electrodes for High-Performance On-Chip Micro-Supercapacitors

The downsizing of microscale energy storage devices is crucial for powering modern on-chip technologies by miniaturizing electronic components. Developing high-performance microscale energy devices, such as micro-supercapacitors, is essential through processing smart electrodes for on-chip structures. In this context, we introduce porous gold (Au) interdigitated electrodes (IDEs) as current collectors for micro-supercapacitors, using polyaniline as the active material. These porous Au IDE-based symmetric micro-supercapacitors (P-SMSCs) show a remarkable enhancement in charge storage performance, with a 187% increase in areal capacitance at 2.5 mA compared to conventional flat Au IDE-based devices, despite identical active material loading times. Our P-SMSCs achieve an areal capacitance of 60 mF/cm2, a peak areal energy density of 5.44 μWh/cm2, and an areal power of 2778 μW/cm2, surpassing most reported SMSCs. This study advances high-performance SMSCs by developing highly porous microscale planar current collectors, optimizing microelectrode use, and maximizing capacity within a compact footprint.

Highly Nanoporous Nickel Foam as Current Collectors in 3D All-Solid-State Microsupercapacitors

This study reports a streamlined method for producing a highly nanoporous current collector with a substantial specific surface area, serving as an electrode for microsupercapacitors (MSCs). Initially, commercial Ni foams are patterned into an interdigitated structure by laser cutting. Subsequently, the Ni foams are infused with NiO nanopowders through dip coating, sintering, and reduction in an H2 atmosphere, followed by the growth of MnO2 through a redox reaction. The incorporation of NiO within this three-dimensional Ni current collector results in notable porosity within the range of approximately 200-600 nm. Such a 3D, highly nanoporous electrode dramatically increases the specific surface area by 30 times and substantially boosts the amount of active material deposition, surpassing those of commercially available Ni foams. Performance evaluations of this highly nanoporous electrode in a 1 M KOH solution demonstrate an areal capacity of 19.3 F/cm2, retaining more than 95% capacitance at 5 mA/cm2, and exhibiting an energy density of 671 μW h/cm2, 25 times greater than commercial Ni foams. Moreover, in the realm of solid-state applications for MSCs, the remarkably high porous electrode achieves a commendable areal capacity of 7.22 F/cm2 and an energy density of 263.9 μW h/cm2, rendering it exceptionally suitable for use in MSC applications.

Planar Micro-Supercapacitors with High Power Density Screen-Printed by Aqueous Graphene Conductive Ink

Simple and scalable production of micro-supercapacitors (MSCs) is crucial to address the energy requirements of miniature electronics. Although significant advancements have been achieved in fabricating MSCs through solution-based printing techniques, the realization of high-performance MSCs remains a challenge. In this paper, graphene-based MSCs with a high power density were prepared through screen printing of aqueous conductive inks with appropriate rheological properties. High electrical conductivity (2.04 × 104 S∙m-1) and low equivalent series resistance (46.7 Ω) benefiting from the dense conductive network consisting of the mesoporous structure formed by graphene with carbon black dispersed as linkers, as well as the narrow finger width and interspace (200 µm) originating from the excellent printability, prompted the fully printed MSCs to deliver high capacitance (9.15 mF∙cm-2), energy density (1.30 µWh∙cm-2) and ultrahigh power density (89.9 mW∙cm-2). Notably, the resulting MSCs can effectively operate at scan rates up to 200 V∙s-1, which surpasses conventional supercapacitors by two orders of magnitude. In addition, the MSCs demonstrate excellent cycling stability (91.6% capacity retention and ~100% Coulombic efficiency after 10,000 cycles) and extraordinary mechanical properties (92.2% capacity retention after 5000 bending cycles), indicating their broad application prospects in flexible wearable/portable electronic systems.

Screen-Printed Stretchable Supercapacitors Based on Tin Sulfide-Decorated Face-Mask-Derived Activated Carbon Electrodes with High Areal Energy Density

In this work, tin sulfide nanosheets decorated on face-mask-derived activated carbon have been explored as electrode material for electrochemical supercapacitors. A hydrothermal route was employed to grow tin sulfide on the surface and inside of high-surface-area face-mask-derived activated carbon, activated at 850 °C, to produce a hierarchical interconnected porous composite (ACFM-850/TS) structure. The presence of tin sulfide in the porous carbon framework exposed the surface active sites for rapid adsorption/desorption of electrolyte ions and ensured high utilization of the porous carbon surface. Furthermore, the porous ACFM-850 framework prevented the stacking/agglomeration of tin sulfide sheets, thereby enhancing the charge-transport kinetics in the composite electrodes. Benefiting from the synergistic effect of tin sulfide and ACFM-850, the resulting ACFM-850/TS composite exhibited an attractive specific capacitance of 423 F g-1 at a 0.5 A g-1 current density and superior rate capability (71.3% at a 30 A g-1 current density) in a 1.0 M Na2SO4 electrolyte. In addition, we fabricated a planar symmetric interdigitated supercapacitor on a stretchable Spandex fabric using an ACFM-850/TS composite electrode and carboxymethyl cellulose/NaClO4 as a solid-state gel electrolyte employing a scalable screen-printing process. The as-prepared stretchable supercapacitors displayed an ultrahigh energy density of 9.2 μWh cm-2 at a power density of 0.13 mW cm-2. In addition, they exhibited an excellent cyclic stability of 64% even after 10,000 charge-discharge cycles and 42% after 1000 continuous stretch (at 25% stretching)/release cycles. Such screen-printed interdigitated planar supercapacitors with activated carbon composite electrodes and a solid-state gel electrolyte act as promising low-cost energy-storage devices for wearable and flexible integrated electronic devices.

Recent Progress and Challenges in Paper-Based Microsupercapacitors for Flexible Electronics: A Comprehensive Review

Recent advances in paper-based microsupercapacitors (p-MSCs) have attracted significant attention due to their potential as substrates for flexible electronics. This review summarizes progress in the field of p-MSCs, discussing their challenges and prospects. It covers various aspects, including the fundamental characteristics of paper, the modification of paper with functional materials, and different methods for device fabrication. The review critically analyzes recent advancements, materials, and fabrication techniques for p-MSCs, exploring their potential applications and benefits, such as flexibility, cost-effectiveness, and sustainability. Additionally, this review highlights gaps in current research, guiding future investigations and innovations in the field. It provides an overview of the current state of p-MSCs and offers valuable insights for researchers and professionals in the field. The critical analysis and discussion presented herein offer a roadmap for the future development of p-MSCs and their potential impact on the domain of flexible electronics.

PANI-Coated VOx Nanobelts with Core-Shell Architecture for Flexible All-Solid-State Supercapacitor

As a typical pseudocapacitor material, VOx possesses mixed valence states, making it an ideal electrode material for symmetric screen-printed supercapacitors. However, its high internal resistance and low energy density are the main hurdles to its widespread application. In this study, a two-dimensional PANI@VOx nanobelt with a core-shell architecture was constructed via a two-step route. This strategy involves the preparation of VOx using a solvothermal method, and a subsequent in situ polymerization process of the PANI. By virtue of the synergistic effect between the VOx core and the PANI shell, the optimal VOx@PANI has an enhanced conductivity of 0.7 ± 0.04 S/Ω, which can deliver a high specific capacitance of 347.5 F/g at 0.5 A/g, a decent cycling life of ~72.0%, and an outstanding Coulomb efficiency of ~100% after 5000 cycles at 5 A/g. Moreover, a flexible all-solid-state symmetric supercapacitor (VOx@PANI SSC) with an in-planar interdigitated structure was screen-printed and assembled on a nickel current collector; it yielded a remarkable areal energy density of 115.17 μWh/cm2 at an areal power density of 0.39 mW/cm2, and possessed outstanding flexibility and mechanical performance. Notably, a "Xiaomi" hygrothermograph (3.0 V) was powered easily by tandem SSCs with an operating voltage of 3.1 V. Therefore, this advanced pseudocapacitor material with core-shell architecture opens novel ideas for flexible symmetric supercapacitors in powering portable/wearable products.

Printed Electronics Based on 2D Material Inks: Preparation, Properties, and Applications toward Memristors

Printed electronics, which fabricate electrical components and circuits on various substrates by leveraging functional inks and advanced printing technologies, have recently attracted tremendous attention due to their capability of large-scale, high-speed, and cost-effective manufacturing and also their great potential in flexible and wearable devices. To further achieve multifunctional, practical, and commercial applications, various printing technologies toward smarter pattern-design, higher resolution, greater production flexibility, and novel ink formulations toward multi-functionalities and high quality have been insensitively investigated. 2D materials, possessing atomically thin thickness, unique properties and excellent solution-processable ability, hold great potential for high-quality inks. Besides, the great variety of 2D materials ranging from metals, semiconductors to insulators offers great freedom to formulate versatile inks to construct various printed electronics. Here, a detailed review of the progress on 2D material inks formulation and its printed applications has been provided, specifically with an emphasis on emerging printed memristors. Finally, the challenges facing the field and prospects of 2D material inks and printed electronics are discussed.

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.

Biocompatible Parylene-C Laser-Induced Graphene Electrodes for Microsupercapacitor Applications

Laser irradiation of polymeric materials has drawn great attention as a fast, simple, and cost-effective method for the formation of porous graphene films that can be subsequently fabricated into low-cost and flexible electronic and energy-storage devices. In this work, we report a systematic study of the formation of laser-induced graphene (LIG) with sheet resistances as low as 9.4 Ω/sq on parylene-C ultrathin membranes under a CO₂ infrared laser. Raman analysis proved the formation of the multilayered graphenic material, with I_D/I_G and I_2D/I_G peak ratios of 0.42 and 0.65, respectively. As a proof of concept, parylene-C LIG was used as the electrode material for the fabrication of ultrathin, solid-state microsupercapacitors (MSCs) via a one-step, scalable, and cost-effective approach, aiming at future flexible and wearable applications. The produced LIG-MSC on parylene-C exhibited good electrochemical behavior, with a specific capacitance of 1.66 mF/cm² and an excellent cycling stability of 96% after 10 000 cycles (0.5 mA/cm²). This work allows one to further extend the knowledge in LIG processes, widening the group of precursor materials as well as promoting future applications. Furthermore, it reinforces the potential of parylene-C as a key material for next-generation biocompatible and flexible electronic devices.

Air-Stable Conductive Polymer Ink for Printed Wearable Micro-Supercapacitors

Printed electronics are expected to facilitate the widespread distributed wearable electronics in the era of the Internet of things. However, developing cheap and stable electrode inks remains a significant challenge in the printed electronics industry and academic community. Here, overcoming the weak hydrophilicity of polyaniline, a low-cost, easy-fabricating, and air-stable conducting polymer (CP) ink is devised through a facile assemble-disperse strategy delivering a high conductivity in the order of 10^-2 S cm^-1 along with a remarkable specific capacitance of 386.9 F g^-1 at 0.5 A g^-1 (dehydrated state). The additive-free CP ink is directly employed to print wearable micro-supercapacitors (MSCs) via the spray-coating method, which deliver a high areal capacitance (96.6 mF cm^-2 ) and volumetric capacitance (26.0 F cm^-3 ), outperforming most state-of-the-art CP-based supercapacitors. This work paves a new approach for achieving scalable MSCs, thus rendering a cost-effective, environmentally friendly, and pervasive energy solution for next-generation distributed electronics.