Electrodes For Micro-supercapacitors Research Articles

Polyaziridine‐Encapsulated Phosphorene‐Incorporated Flexible 3D Porous Graphene for Multimodal Sensing and Energy Storage Applications

AbstractHeteroatom‐incorporated graphene represents a prominent family of materials utilized as active electrodes for multimodal sensing and energy storage applications. Herein, a novel polyaziridine‐encapsulated phosphorene (PEP)‐incorporated flexible 3D porous graphene (3DPG) electrode is developed using facile, cost‐effective laser writing, and drop‐casting techniques. Owing to the excellent electrochemical characteristics and surface functionality of the highly stable PEP, the fabricated PEP/3DPG is evaluated as a potential electrode for immunosensing, electrocardiogram (ECG) recording, and microsupercapacitors (MSCs). Under optimized conditions, the produced PEP/3DPG‐based carcinoembryonic immunosensor exhibits linear ranges of 0.1–700 pg mL−1 and 1–100 ng mL−1 with a detection limit of 0.34 pg mL−1 and high selectivity. The finger touch‐based ECG sensor demonstrates a relatively low and stable impedance at the skin‐electrode interface; therefore, the signal‐to‐noise ratio of the ECG signal received from the fabricated sensor (13.5 dB) is comparable to that of conventional Ag/AgCl electrodes (13.9 dB). Besides, the highest areal capacitance of the prepared MSC reached a magnitude of 16.94 mF cm−2, which is six times higher than that of a non‐doped 3DPG‐based MSC. These results demonstrate the effectiveness of the described fabrication procedure and the high utilization potential of the encapsulated phosphorene‐doped 3D graphene in multimodal applications.

Novel fabrication method of hierarchical planar micro-supercapacitor via laser-induced localized growth of manganese dioxide nanowire arrays

Micro-supercapacitors are enormously needed, owing to increasing energy demands in miniaturizing mobile electronic devices. Manganese dioxide (MnO2) is one of the most popular micro-supercapacitor electrode materials that can be applied with various fabrication methods. However, in case of the conventional fabrication of MnO2-based micro-supercapacitor, fabrication methods require complex multiple steps or sophisticated patterning techniques for MnO2 selective micro-patterning. Thus, it is difficult to improve space utilization of micro-supercapacitor and apply them to further another application. In this study, we introduce a novel fabrication method of hierarchical planar micro-supercapacitor using MnO2 nanowire (NW) arrays. Using laser-induced hydrothermal growth (LIHG) process, MnO2 NW arrays are vertically grown on selective area in the desired location under ambient conditions. For the stable growth of vertically aligned MnO2 NW array using LIHG process, various laser parameters, including irradiation time and power, are adjusted. Afterward, the vertically grown MnO2 NW arrays are applied to fabricate hierarchical planar micro-supercapacitor, showing high areal capacitance of 227 mF cm−2 (at 1 mA cm−2) in terms of footprint area on tiny 2D plane. Thus, the proposed approach can be considered as a new fabrication method for capacitance enhancement of planar micro-supercapacitor.

RF Sputter-Deposited Nanostructured CuO Films for Micro-Supercapacitors

Copper oxide is considered as an alternative electrode material for supercapacitors due to its low cost, chemical stability and high theoretical specific capacitance. In the present work, nanostructured copper oxide (CuO) films are prepared by radio-frequency (RF) magnetron sputtering, and the influence of the substrate temperature on the microstructure and supercapacitive properties was studied. The copper oxide films prepared at 350 °C exhibit a predominant (1¯11) orientation corresponding to the monoclinic Cu(II)O phase with a crystallite size of 24 nm. The surface of the film consists of uniformly distributed oval-like grains providing a high surface roughness of 45 nm. The films exhibit an optical bandgap of 1.68 ± 0.01 eV and an electrical conductivity of 0.4 S cm−1 at room temperature. The as-prepared CuO films deliver a discharge specific capacitance of 387 mF cm−2 (375 F g−1) at a current density of 1 mA cm−2 with excellent cyclic capacitance retention of 95% (367 mF cm−2) even after 1000 cycles. Hence, these films are potential electrodes for micro-supercapacitors.

B/N-Enriched Semi-Conductive Polymer Film for Micro-Supercapacitors with AC Line-Filtering Performance.

Microsupercapacitors (MSCs) have drawn great attention for use as miniaturized electrochemical energy storage devices in portable, wearable, as well as implantable electronics. Many materials have been developed as electrodes for MSCs. However, the thin-film fabrication for most of these materials involves multistep operations, including filtration, spray coating, and sputtering. Most importantly, these methods present challenges for the preparation of thin films at the atomic or molecular scale. Therefore, the understanding of performance of ultrathin-film-based MSCs remains challenge. Herein, a B/N-enriched polymer film is successfully prepared using the photoassisted interfacial approach. The as-synthesized polymer film exhibits typical semiconductive characteristics and can be easily scaled up to a large area of up to tens of square centimeters. This ultrathin polymer film can be directly transferred to silicon wafers to fabricate MSC through laser scribing. The prepared MSC exhibits specific volumetric capacitance as high as 20.9 F cm-3, corresponding to volumetric energy density of 2.9 mWh cm-3 (at 0.1 V s-1). Moreover, the volumetric power density can reach 1461 W cm-3, surpassing most existing semiconductive polymer film-based MSC devices. In addition, the prepared MSC exhibits typical AC line-filtering ability (-67° at 120 Hz). This study offers a facile interfacial approach to preparing semiconductive polymer films with aromatic moieties for microsized energy storage devices.

Highly Porous Scaffolds for Ru-Based Microsupercapacitor Electrodes Using Hydrogen Bubble Templated Electrodeposition

Highly Porous Scaffolds for Ru-Based Microsupercapacitor Electrodes Using Hydrogen Bubble Templated Electrodeposition

Porous RuOxNySz Electrodes for Microsupercapacitors and Microbatteries with Enhanced Areal Performance

Three-dimensional (3D) electrodes with improved areal energy have become increasingly important for microscale energy storage at the dawn of the Internet of Things. At its heart are a plethora of microelectronic devices that require embedded energy harvesters and energy storage components to ensure autonomy. In this study, we develop porous metallic microstructures and their conformal coating with a new RuOxNySz material through a facile optimized electrodeposition process. The microporous structure with a nanodendritic network shows high areal capacitance (14.3 F cm–2 for the electrode and 714 mF cm–2 for an all-solid-state microsupercacitor) and stable performance (>80% retention after 5000 cycles) toward H+ storage. Remarkable Li+ storage capability with high areal capacity (5 mAh cm–2) and rate characteristics (1.5 mAh cm–2 at 3C) is also observed. These results coupled with a facile synthetic strategy can thus offer inspiration for large-scale production of 3D porous electrodes for microbatteries and microsupercapacitors.

Laser direct preparation and processing of graphene/MnO nanocomposite electrodes for microsupercapacitors

Graphene/metal oxide nanocomposites are one of the most ideal electrode materials for microsupercapacitors (MSCs). However, the efficient and simple synthesis of graphene/metal oxide nanocomposites and fabrication of microelectrodes for MSCs are a challenge. In this work, using graphene oxide/Mn(CH3COO)2 as the precursor, an efficient and simple approach is proposed to simultaneously synthesize graphene/MnO nanocomposites and process interdigital electrodes for MSCs by one-step picosecond laser direct-writing. Here, the MnO nanoparticles that are evenly distributed on the surface of graphene can provide pseudocapacitance to enhance the specific capacitance of graphene/MnO nanocomposites. Specifically, graphene/MnO electrode exhibits a high specific capacitance of 470 mF cm−2. Furthermore, based on graphene/MnO interdigital electrodes, the symmetric MSCs shows excellent electrochemical performance. The maximum area specific capacitance of MSCs with PVA/H3PO4 gel electrolyte is 55 mF cm−2. After 5000 cycles, the capacitance of the MSCs with PVA/H3PO4 gel electrolyte retains about 96% of its initial capacitance. The maximum energy density of MSCs with PVA/H3PO4 gel electrolyte is 4.89 μWh cm−2, and its maximum power density is 0.72 mW cm−2. Moreover, this approach also provides a way to synthesize other graphene/metal oxide nanocomposites for MSCs by one-step laser direct-writing.

Laser Scribing of Fluorinated Polyimide Films to Generate Microporous Structures for High-Performance Micro-supercapacitor Electrodes

Laser-induced graphene (LIG) typically exhibits a mesostructure with a small specific surface area, which is detrimental to the electrochemical performance of micro-supercapacitors (MSCs). Herein, ...

Double Approach Towards 3D Electrodeposited RuOx Porous Structure for High Energy/High Power Micro-Supercapacitors

Hydrous RuOx has been one of the well-studied materials for application in supercapacitors owing to its excellent properties (high conductivity similar to metals, redox activity capable of fast faradaic reactions and structural water enabling swift proton transfer and decreased diffusion distance). The main issue regarding supercapacitors is that, they suffer from low energy density compared to batteries. One way to overcome this problem is to increase surface area of the active material and hence the energy stored through 3D structuration of current collector. Multiple techniques have been used in this regard like 3D printing, pholitography methods...etc.However, these techniques are pretty complex, time consuming and have constraining conditions. Hence, it’s necessary to develop economic and simple routes for 3D structuration of electrodes for micro-supercapacitors. One simple, time efficient and easy to set up method that can be used under ambient conditions is the electrochemical structuration using dynamic hydrogen bubble template (DHBT). With this strategy, 3D scaffolds which can hold small quantities of intrinsic pseudocapacitve materials like RuOx can be fabricated. The challenge in this latter case is magnified, needing controlled decoration of active materials for efficient utilization and full benefit of the 3D framework. Hence, the pursuit of superior micro-supercapacitors not only needs controlled deposition, but also requires stable 3D scaffolds to maximize capacitance per footprint area1. We have previously shown electrodeposition of active RuO2 on porous gold electrodes for micro-supercapacitors achieving a capacitance of 3 F/cm².One other approach would be to deposit the active material directly by the DHBT method. As RuOx is a good conductor this would not hinder its efficiency (this would not be the case for MnO2 for example). The difficulty here is that, not all metals can be deposited by the DHBT technique as other factors play a crucial role such as the exchanged current density towards H2 evolution and mechanical stability3 In the current work, we report two different strategies for the 3D deposition of RuOx. The first is the successful fabrication of highly porous 3D platinum current collector using DHBT followed by a conformal coating of hydrous RuOx to achieve a specific capacitance as high as 10 F/cm². The second is the direct electrodeposition of the active material, RuOx, in a 3D porous structure. These two approaches are characterized and discussed within the framework of fabricating superior micro-supercapacitors with excellent capacitance and low internal resistance. References N. A. Kyeremateng, T. Brousse, and D. Pech, Nat. Nanotechnol., 12, 7–15 (2017)A. Ferris, S. Garbarino, D. Guay, and D. Pech, Adv. Mater., 27, 6625–6629 (2015)Plowman, B. J., Jones, L. A., & Bhargava, S. K. Chem. Commun., 51(21), 4331–4346. Figure 1

3D printed hybrid-dimensional electrodes for flexible micro-supercapacitors with superior electrochemical behaviours

ABSTRACT Micro-supercapacitors (MSCs) with excellent electrochemical behaviours and flexibility possess great promise for portable and wearable electronic devices. A novel type of hybrid-dimensional Fe2O3/graphene/Ag ink is developed and extruded into MSC electrodes through the direct ink writing-based three-dimensional (3D) printing. The optimal solid-state MSC device exhibits a maximum areal capacitance of 412.3 mF cm−2 at 2 mA cm−2, a correspondingly high energy density of 65.4 μWh cm−2 and 89% capacitance retention for over 5000 charge and discharge cycles. The superior electrochemical performance is profited by the high electron transport synergistically boosted by two-dimensional graphene nanosheets and one-dimensional Ag nanowires, and the high pseudocapacitive behaviours of Fe2O3 nanoparticles. The 3D printed MSC exhibits reliable flexibility with remarkable retention of 90.2% of its original capacitance after 500 bending cycles. The current 3D printing fabrication demonstrates an efficient route for advanced miniaturised electrochemical energy storage.

Structural Engineering and Coupling of Two-Dimensional Transition Metal Compounds for Micro-Supercapacitor Electrodes.

The development of portable, wearable, and miniaturized integrated electronics has significantly promoted the immense desire for planar micro-supercapacitors (MSCs) among the extremely competitive energy storage devices. However, their energy density is still insufficient owing to the low electrochemical performance of conventional electrode materials. Compared with their bulk counterparts, the large specific surface area and fast ion transport with efficient intercalation of two-dimensional (2D) transition metal compounds have spurred the research platforms for their exploitation in the creation of high-performance MSCs. This Outlook presents a systematic summary of cutting-edge research on atomically thin, layered structures of transition metal dichalcogenides, MXenes, and transition metal oxides/hydroxides. Special emphasis is given to the rapid and durable storage of ions, benefiting from the low ion diffusion barriers of host interlayer spaces. Moreover, various strategies have been described to circumvent the structural damage due to the volume change and simultaneously evincing remarkable electronic properties.

Direct Assembly of 3D-BCN Microspheres as a Microsupercapacitor Electrode for Wearable Energy Storage.

Scalable and cost-effective fabrication of three-dimensional (3D) boron carbon nitride (BCN) microspheres was first demonstrated by hydrothermal and annealing methods. In particular, the specific surface area of 3D-BCN-4 reached 1390.12 m2 g-1 and had a high hierarchical pore structure. An all-printed solid-state flexible microsupercapacitor (MSC) based on 3D-BCN-4 microspheres as an electrode material was fabricated for the first time by a screen printing method, which also provided efficacious properties. The single MSC areal capacitance reached 41.6 mF cm-2. Furthermore, the remarkable mechanical flexibility was also achieved for the device with evidence that no obvious capacitance loss occurred even upon bending to 180°, and the device had a 93.3% capacitance retention after 1000 cycles. In addition, the maximum energy density reached 0.00832 mW h cm-2, and the highest power density was 2 mW cm-2. These results show the synthesis of 3D-BCN by a facile and effective method with excellent electrochemical performance, which should provide a promising direction to wearable energy storage devices.

Robust and durable flexible micro-supercapacitors enabled by graphene nanoscrolls

The rise of miniaturized, flexible and self-powered electronic systems has substantially stimulated the urgent demand for microscale electrochemical energy storage devices. Impressively, planar micro-supercapacitors (MSCs) are playing a crucial role because of fast ion transmission, ultra-long lifetime, and being easily integrated with microelectronic devices. Unfortunately, the robustness of film electrodes in MSCs usually cannot satisfy the structural stability of the film electrodes and the durability of the devices. Here, a novel strategy to address the problem is proposed by introducing graphene nanoscrolls with high aspect ratio as the active materials in the flexible MSCs to enhance the robustness of the film electrode because of their intertwined one-dimensional nanostructures. The as-prepared bendable MSC can maintain nearly 100% of initial capacitance when bent for 1000 cycles, and the stretchable MSC can maintain 88% of initial capacitance when stretched at a high stress ratio of 100% for 1000 cycles. This study provides an effective strategy to build up robust film electrodes for MSCs and improve the durability of the flexible MSCs.

Laser Pyrolysis of Imprinted Furan Pattern for the Precise Fabrication of Microsupercapacitor Electrodes

The design or dimension of micro-supercapacitor electrodes is an important factor that determines their performance. In this study, a microsupercapacitor was precisely fabricated on a silicon substrate by irradiating an imprinted furan micropattern with a CO2 laser beam under ambient conditions. Since furan is a carbon-abundant polymer, electrically conductive and porous carbon structures were produced by laser-induced pyrolysis. While the pyrolysis of a furan film in a general electric furnace resulted in severe cracks and delamination, the laser pyrolysis method proposed herein yielded porous carbon films without cracks or delamination. Moreover, as the imprinting process already designated the furan area for laser pyrolysis, high-precision patterning was achieved in the subsequent laser pyrolysis step. This two-step process exploited the superior resolution of imprinting for the fabrication of a laser-pyrolyzed carbon micropattern. As a result, the technical limitations of conventional laser direct writing could be overcome. The laser-pyrolyzed carbon structure was employed for microsupercapacitor electrodes. The microsupercapacitor showed a specific capacitance of 0.92 mF/cm2 at 1 mA/cm2 with a PVA-H2SO4 gel electrolyte, and retained an up to 88% capacitance after 10,000 charging/discharging cycles.

Boosting areal energy density of 3D printed all-solid-state flexible microsupercapacitors via tailoring graphene composition

Tailoring the composition of graphene used as electrodes for microsupercapacitors is an effective solution to increase the areal energy density of the devices for greater advancement towards miniaturized electronic applications. Herein, we demonstrate a simple method to prepare the nitrogen/oxygen-doped graphene ink for the scalable 3D printed all-solid-state flexible microsupercapacitors. The devices show promising electrochemical performance with high areal energy density of 2.59 ​μWh cm−2 and power density of 0.23 ​mW ​cm−2, good cycling stability, and excellent mechanical flexibility. The method developed here offers a new avenue for the development of high-performance, all-solid-state flexible microsupercapacitors in a straightforward and scalable process.

Double Approach Towards 3D Electrodeposited RuOx Porous Structure for High Energy/High Power Micro-Supercapacitors

Hydrous RuOx has been one of the well-studied materials for application in supercapacitors owing to its excellent properties (high conductivity similar to metals, redox activity capable of fast faradaic reactions and structural water enabling swift proton transfer and decreased diffusion distance). The main issue regarding supercapacitors is that, they suffer from low energy density compared to batteries. One way to overcome this problem is to increase surface area of the active material and hence the energy stored through 3D structuration of current collector. Multiple techniques have been used in this regard like 3D printing, pholitography methods...etc. However, these techniques are pretty complex, time consuming and have constraining conditions. Hence, it’s necessary to develop economic and simple routes for 3D structuration of electrodes for micro-supercapacitors. One simple, time efficient and easy to set up method that can be used under ambient conditions is the electrochemical structuration using dynamic hydrogen bubble template (DHBT). With this strategy, 3D scaffolds which can hold small quantities of intrinsic pseudocapacitve materials like RuOx can be fabricated. The challenge in this latter case is magnified, needing controlled decoration of active materials for efficient utilization and full benefit of the 3D framework. Hence, the pursuit of superior micro-supercapacitors not only needs controlled deposition, but also requires stable 3D scaffolds to maximize capacitance per footprint area1. We have previously shown electrodeposition of active RuOx on porous gold electrodes for micro-supercapacitors achieving a capacitance of 3 F/cm².2 One other approach would be to deposit the active material directly by the DHBT method. As RuOx is a good conductor this would not hinder its efficiency (this would not be the case for MnO2 for example). The difficulty here is that, not all metals can be deposited by the DHBT technique as other factors play a crucial role such as the exchanged current density towards H2 evolution and mechanical stability3. In the current work, we report two different strategies for the 3D deposition of RuOx. The first is the successful fabrication of highly porous 3D platinum current collector using DHBT followed by a conformal coating of hydrous RuOx to achieve a specific capacitance as high as 7 F/cm². The second is the direct electrodeposition of the active material, RuOx, in a 3D porous structure. These two approaches are characterized and discussed within the framework of fabricating superior micro-supercapacitors with excellent capacitance and low internal resistance.

High Capacitive PEDOT-Coated SiNWs Electrode for Micro-supercapacitors with Facile Preparation

Si nanostructures have drawn considerable attention in the field of Micro-supercapacitors. In this work, a hybrid electrode based on poly(3,4-ethylenedioxythiophene) (PEDOT) coated silicon nanowire arrays (SiNWs) is prepared via a two-step process. The SiNWs are synthesized by metal-assisted electroless etching method and treated by the tetramethylammonium hydroxide (TMAH) solution. Then, the porous PEDOT film is electrodeposited from the ionic liquid electrolyte. The influence of SiNWs and the oligomers in the electrolyte on the morphology of the hybrid electrode and/or on the contact/adhesin between PEDOT and SiNWs are systematically investigated for the first time. Additionally, the storage mechanism of the hybrid electrode is also investigated. After optimization, the hybrid electrode delivers a specific capacitance as high as 115 mF/cm2 at the current density of 0.5 mA/cm2, comparing to the top values of previously reported Si nanostructure electrodes. These preliminary results demonstrate that each component provides unique and crucial function to achieve optimized electrochemical properties, benefiting to fabricate high capacitive performance of Si nanostructure Micro-supercapacitors with simple and low-cost approaches.

3D knitted energy storage textiles using MXene-coated yarns

Abstract Textile-based energy storage devices offer an exciting replacement for bulky and uncomfortable batteries in commercial smart garments. Fiber and yarn-based supercapacitors, currently dominating research in this field, have demonstrated excellent performance below ∼4 cm in length, but suffer at longer lengths due to increased resistance. Herein, a new architecture of wearable energy storage devices, 3D knitted supercapacitors, is designed and prototyped with the intention of exploiting the architecture of a knit textile to improve the performance of long yarn electrodes. While Computer-Aided Design (CAD) knitting is a ubiquitous technology for producing textiles, knitted energy storage devices have been largely unexplored due to the need for meters of highly conductive yarn electrodes that meet the strenuous strength and flexibility requirements for CAD knitting. MXenes, a family of solution processable and conductive two-dimensional (2D) materials, have been realized as inks, slurries, pastes, and now dyes for the development of on-paper, on-plastic, and on-textile microsupercapacitor electrodes. In this work, Ti3C2Tx MXene was adopted as an active material for coating meters of commercial natural and synthetic yarns, enabling the production of knitted planar microsupercapacitors. The impact on electrochemical performance of knit structure and geometry was systematically studied in an attempt to produce energy storing textiles with power and energy densities that can be used for practical applications. The resulting energy storing textiles demonstrate high capacitance, up to 707 mF cm−2 and 519 mF cm−2 at 2 mV s−1 in 1 M H3PO4 and PVA-H3PO4 gel electrolyte, respectively, and excellent cycling stability over 10,000 cycles. This work represents an important step towards the mass production of MXene-based conductive yarns and 3D knitted energy storage devices and demonstrates how knit structure plays a significant role on device performance.

Quasi-aligned SiC@C nanowire arrays as free-standing electrodes for high-performance micro-supercapacitors

Currently, it still remains a grand challenge to enhance energy density of micro-supercapacitors (MSCs) without sacrificing power density, cycle life and other key performance. Herein, we reported the exploration of free-standing electrodes for MSCs based on quasi-aligned SiC nanowire arrays wrapped by ultrathin graphitic carbon film (SiC@C). Such rationally designed SiC@C architecture bring an optimal specific capacitance of 78.98 mF cm−2 at a current density of 0.2 mA cm−2, which was enhanced by more than 700% in comparison to that of pure SiC counterpart (9.56 mF cm−2). The aqueous-based MSCs exhibit a high specific capacitance, fast charge-discharge rate, excellent rate capability, and long-term cycling stability (94.1% capacity retention after 10000 charge-discharge cycles). The ionic-liquid-based MSCs had an extended operating voltage up to 2.6 V with an energy density up to 2.84 μW h cm−2 (at a power density of 65.1 μW cm−2), which was a new record of SiC-based SCs, and superior to most of those of nanowire-based MSCs in other material systems ever reported.

A direct-write method for preparing a bimetal sulfide/graphene composite as a free-standing electrode for high-performance microsupercapacitors.

It is a great challenge to ideally integrate graphene with its unique two-dimensional (2D) and porous structure into the pseudocapacitive materials. In this paper, a simple technique, i.e. direct-laser-writing (DLW), was developed to fabricate microsupercapacitors (MSCs) with excellent electrochemical performance, marked as Ni–Co–S/laser induced graphene (LIG) that exhibit a high areal specific capacitance of 680 mF cm−2 at the current density of 1 mA cm−2. A symmetric MSC device was assembled using Ni–Co–S/LIG as a positive electrode and active carbon (AC) as the negative electrode, and exhibited a high areal energy density of 56.9 μW h cm−2 at the power density of 800 μW cm−2, and excellent cycling stability maintaining 89.6% of the areal specific capacitance after 8000 cycles. The synergistic effect of bimetallic Ni–Co–S and the LIG with the 2D structure results in the excellent electrochemical performance. This work demonstrates a method to integrate Ni–Co–S pseudocapacitive materials into porous graphene with a direct-laser-writing technique. The produced integrated materials possess high energy density that can be used in MSCs.