Electrochemically active porous carbon nanospheres prepared by inhibition of pyrolytic condensation of polymers.

Porous carbon is a pivotal material for electrochemical applications. The manufacture of porous carbon has relied on chemical treatments (etching or template) that require processing in all areas of the carbon/carbon precursor. We present a unique approach to preparing porous carbon nanospheres by inhibiting the pyrolytic condensation of polymers. Specifically, the porous carbon nanospheres are obtained by coating a thin film of ZnO on polystyrene spheres. The porosity of the porous carbon nanospheres is controlled by the thickness of the ZnO shell, achieving a BET-specific area of 1,124 m2/g with a specific volume of 1.09 cm3/g. We confirm that under the support force by the ZnO shell, a hierarchical pore structure in which small mesopores are connected by large mesopores is formed and that the pore-associated sp3 defects are enriched. These features allow full utilization of the surface area of the carbon pores. The electrochemical capacitive performance of porous carbon nanospheres was evaluated, achieving a high capacitance of 389 F/g at 1 A/g, capacitance retention of 71% at a 20-fold increase in current density, and stability up to 30,000 cycles. In particular, we achieve a specific area-normalized capacitance of 34.6 µF/cm2, which overcomes the limitations of conventional carbon materials.

Carbon-cement supercapacitors as a scalable bulk energy storage solution.

The large-scale implementation of renewable energy systems necessitates the development of energy storage solutions to effectively manage imbalances between energy supply and demand. Herein, we investigate such a scalable material solution for energy storage in supercapacitors constructed from readily available material precursors that can be locally sourced from virtually anywhere on the planet, namely cement, water, and carbon black. We characterize our carbon-cement electrodes by combining correlative EDS-Raman spectroscopy with capacitance measurements derived from cyclic voltammetry and galvanostatic charge-discharge experiments using integer and fractional derivatives to correct for rate and current intensity effects. Texture analysis reveals that the hydration reactions of cement in the presence of carbon generate a fractal-like electron-conducting carbon network that permeates the load-bearing cement-based matrix. The energy storage capacity of this space-filling carbon black network of the high specific surface area accessible to charge storage is shown to be an intensive quantity, whereas the high-rate capability of the carbon-cement electrodes exhibits self-similarity due to the hydration porosity available for charge transport. This intensive and self-similar nature of energy storage and rate capability represents an opportunity for mass scaling from electrode to structural scales. The availability, versatility, and scalability of these carbon-cement supercapacitors opens a horizon for the design of multifunctional structures that leverage high energy storage capacity, high-rate charge/discharge capabilities, and structural strength for sustainable residential and industrial applications ranging from energy autarkic shelters and self-charging roads for electric vehicles, to intermittent energy storage for wind turbines and tidal power stations.

How chemical defects influence the charging of nanoporous carbon supercapacitors.

SignificanceNanoporous carbon texture makes fundamental understanding of the electrochemical processes challenging. Based on density functional theory (DFT) results, the proposed atomistic approach takes into account topological and chemical defects of the electrodes and attributes to them a partial charge that depends on the applied voltage. Using a realistic carbon nanotexture, a model is developed to simulate the ionic charge both at the surface and in the subnanometric pores of the electrodes of a supercapacitor. Before entering the smallest pores, ions dehydrate at the external surface of the electrodes, leading to asymmetric adsorption behavior. Ions in subnanometric pores are mostly fully dehydrated. The simulated capacitance is in qualitative agreement with experiments. Part of these ions remain irreversibly trapped upon discharge.

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.

Ultrarapid Gelation of Porous Ti3C2Tx MXene Monoliths Induced by Ionic Liquids.

Gelation is a promising method to assemble 3D macroscopic structures from MXene sheets for various applications. However, the fine control and scalable manufacturing of 3D MXene monoliths remains a great challenge. Herein, the controllable gelation of Ti3C2Tx MXene initiated by various ionic liquids (ILs) is first proposed, where the IL serve as linkers to bond the nanosheets together through electrostatic and hydrogen bonding interactions, forming 3D monoliths with well-adjustable structure. Furthermore, density functional theory calculations and experiments further reveal the cross-linking effect of different ILs. Typically, 3D porous structure with high specific surface area, suitable pore size, and improved electrolyte affinity is designed through the cross-linking of Ti3C2Tx with 1-vinyl-3-ethylimidazole bromide ([C2VIm]Br-Ti3C2Tx). Due to the strong coupling, the as-synthesized monolith possesses excellent rate performance and high energy density. The methodology is quite flexible, controllable, and universal that provides a new perspective for promoting innovative applications of 2D materials.

Proton is Essential or Not: A Fresh Look on Pseudocapacitive Energy Storage of PANI Composites.

Protonation has been considered essential for the pseudocapacitive energy storage of polyaniline (PANI) for years, as proton doping in PANI chains not only activates electron transport pathways, but also promotes the proceeding of redox reactions. Rarely has the ability for PANI of storing energy without protonation been investigated, and it remains uncertain whether PANI has pseudocapacitive charge storage properties in an alkaline electrolyte. Here, this work first demonstrates the pseudocapacitive energy storage for PANI without protonation using a PANI/graphene composite as a model material in an alkaline electrolyte. Using in situ Raman spectroscopy coupled with electrochemical quartz crystal microbalance (EQCM) measurements, this work determines the formation of -N= group over potential on a PANI chain and demonstrates the direct contribution of OH- in the nonprotonation type of oxidation reactions. This work finds that the PANI/graphene composite in an alkaline electrolyte has excellent cycling stability with a wider operation voltage of 1 V as well as a slightly higher specific capacitance than that in an acidic electrolyte. The findings provide a new perspective on pseudocapacitive energy storage of PANI-based composites, which will influence the selection of electrolytes for PANI materials and expand their application in energy storage fields.

High Capacitance Porous Ruthenium Nitride Films with High Rate Capability for Micro-Supercapacitors.

The demand for high-performance energy storage devices to power Internet of Things applications has driven intensive research on micro-supercapacitors (MSCs). In this study, RuN films made by magnetron sputtering as an efficient electrode material for MSCs are investigated. The sputtering parameters are carefully studied in order to maximize film porosity while maintaining high electrical conductivity, enabling a fast charging process. Using a combination of advanced techniques, the relationships among the morphology, structure, and electrochemical properties of the RuN films are investigated. The films are shown to have a complex structure containing a mixture of crystallized Ru and RuN phases with an amorphous oxide layer. The combination of high electrical conductivity and pseudocapacitive charge storage properties enabled a 16 µm-thick RuN film to achieve a capacitance value of 0.8 F cm-2 in 1 m KOH with ultra-high rate capability.

Morphology Control of Mixed Metallic Organic Framework for High-Performance Hybrid Supercapacitors.

The study presents the binder-free synthesis of mixed metallic organic frameworks (MMOFs) supported on a ternary metal oxide (TMO) core as an innovative three-dimensional (3D) approach to enhance electron transport and mass transfer during the electrochemical charge-discharge process, resulting in high-performance hybrid supercapacitors. The research demonstrates that the choice of organic linkers can be used to tailor the morphology of these MMOFs, thus optimizing their electrochemical efficiency. Specifically, a NiCo-MOF@NiCoO2@Ni electrode, based on terephthalic linkers, exhibits highly ordered porosity and a vast internal surface area, achieving a maximum specific capacity of 2320 mC cm-2, while maintaining excellent rate capability and cycle stability. With these performances, the hybrid supercapacitor (HSC) achieves a maximum specific capacitance of 424.6 mF cm-2 (specific capacity 653.8 mC cm-2) and 30.7 F cm-3 with energy density values of 10.1 mWh cm-3 at 167.4 mW cm-3 (139.8 µWh cm-2 at 2310 µW cm-2), which are higher than those of previously reported MMOFs based electrodes. This research introduces a novel approach for metal organic framework based HSC electrodes, diverging from the traditional emphasis on metal ions, in order to achieve the desired electrochemical performance.

Leaf-Inspired Hetero-Structure WS2/WO3 In Situ Embedded on Pomelo Peel Derived Carbon for Supercapacitor and Capacitive Deionization.

Composite materials have occupied a reliable position in electrochemical energy storage and conversion due to their double electric layer and pseudocapacitance. In this work, a leaf-like heterostructure composite, obtained by peeling - carbonizing - in situ sulfuration/oxidation approach for the first time, is investigated as electrode material for electrochemical capacitance behavior. The thin and highly active transition metal WS2 acts as an energetic "blade" to trap free ions, which are then transported across the material through a strong "tendon skeleton" WO3. The derived carbon PPC with a large aspect ratio holds up the overall leaf structure, also as a "warehouse" for ion storage, thus enhancing the conductivity and wettability of the material. The above three (WS2+WO3+PPC) synergistically provide outstanding double-layer capacitance and pseudocapacitance. In particular, the vacancy defects, constructed at the heterogenous interface from WS2-WO3 in situ growth, can still achieve superior ion absorption/desorption ability even under large current density and high concentration brackish solution.

Microwave Doping of Sulfur and Iron in ß12 Borophene.

Borophene, a 2D material exhibiting unique crystallographic phases like the anisotropic atomic lattices of ß12 and X3 phases, has attracted considerable attention due to its intriguing Dirac nature and metallic attributes. Despite surpassing graphene in electronic mobility, borophene's potential in energy storage and catalysis remains untapped due to its inherent electrochemical and catalytic limitations. Elemental doping emerges as a promising strategy to introduce charge carriers, enabling localized electrochemical and catalytic functionalities. However, effective doping of borophene has been a complex and underexplored challenge. Here, an innovative, one-pot microwave-assisted doping method, tailored for the ß12 phase of borophene is introduced. By subjecting dispersed ß12 borophene in dimethylformamide to controlled microwave exposure with sulfur powder and FeCl3 as doping precursors, S- and Fe doping in borophene can be controlled. Employing advanced techniques including high-resolution transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, confirm successful sulfur and iron dopant incorporation onto ß12 borophene is confirmed, achieving doping levels of up to 11 % and 13 %, respectively. Remarkably, S- and Fe-doped borophene exhibit exceptional supercapacitive behavior, with specific capacitances of 202 and 120 F g-1 , respectively, at a moderate current density of 0.25 A g-1 .

Hierarchical Hollow Carbon Particles with Encapsulation of Carbon Nanotubes for High Performance Supercapacitors.

A novel and sustainable carbon-based material, referred to as hollow porous carbon particles encapsulating multi-wall carbon nanotubes (MWCNTs) (CNTs@HPC), is synthesized for use in supercapacitors. The synthesis process involves utilizing LTA zeolite as a rigid template and dopamine hydrochloride (DA) as the carbon source, along with catalytic decomposition of methane (CDM) to simultaneously produce MWCNTs and COx -free H2 . The findings reveal a distinctive hierarchical porous structure, comprising macropores, mesopores, and micropores, resulting in a total specific surface area (SSA) of 913 m2  g-1 . The optimal CNTs@HPC demonstrates a specific capacitance of 306 F g-1 at a current density of 1 A g-1 . Moreover, this material demonstrates an electric double-layer capacitor (EDLC) that surpasses conventional capabilities by exhibiting additional pseudocapacitance characteristics. These properties are attributed to redox reactions facilitated by the increased charge density resulting from the attraction of ions to nickel oxides, which is made possible by the material's enhanced hydrophilicity. The heightened hydrophilicity can be attributed to the presence of residual silicon-aluminum elements in CNTs@HPC, a direct outcome of the unique synthesis approach involving nickel phyllosilicate in CDM. As a result of this synthesis strategy, the material possesses excellent conductivity, enabling rapid transportation of electrolyte ions and delivering outstanding capacitive performance.

Unlocking the Effect of Chain Length and Terminal Group on Ethylene Glycol Ether Family Toward Advanced Aqueous Electrolytes.

Constructing high-performance hybrid electrolyte is important to advanced aqueous electrochemical energy storage devices. However, due to the lack of in-depth understanding of how the molecule structures of cosolvent additives influence the properties of electrolytes significantly impeded the development of hybrid electrolytes. Herein, a series of hybrid electrolytes are prepared by using ethylene glycol ether with different chain lengths and terminal groups as additives. The optimized 2 m LiTFSI-90%DDm hybrid electrolyte prepared from diethylene glycol dimethyl ether (DDm) molecule showcases excellent comprehensive performance and significantly enhances the operating voltage of supercapacitors (SCs) to 2.5 V by suppressing the activity of water. Moreover, the SC with 2 m LiTFSI-90%DDm hybrid electrolyte supplies a long-term cycling life of 50 000 cycles at 1 A g-1 with 92.3% capacitance retention as well as excellent low temperature (-40 ºC) cycling performance (10 000 times at 0.2 A g-1). Universally, Zn//polyaniline full cell with 2 m Zn(OTf)2-90%DDm electrolyte manifests outstanding cycling performance in terms of 77.9% capacity retention after 2,000 cycles and a dendrite-free Zn anode. This work inspires new thinking of developing advanced hybrid electrolytes by cosolvent molecule design toward high-performance energy storage devices.

Gas Phase-Heat Absorption-Condensate Phase Stepwise Flame Retardant Strategy to Prepare Coal Tar Pitch-Based Porous Carbon for Supercapacitor.

Porous carbon is widely used in energy storage-conversion systems, and the question of how to explore an efficient strategy for preparation is very significant. Herein, the flame retardant capability of (NH4 )2 SO4 /Mg(OH)2 that contains gas phase-heat absorption-condensate phase components is assisted to carbonize coal tar pitch in air and obtain the porous carbon. The mechanism of stepwise inflaming retarding is systematically investigated. In the carbonization process in a muffle furnace, (NH4 )2 SO4 decomposes releasing gases at below 400 °C to act as the role of gas phase flame retardant. Mg(OH)2 starts to decompose at ≥ 400 °C, and it has the effect of heat absorption and condensed phase flame retardation (MgSO4 and MgO). What's more, the flame retardant also serves as an N, S source and template. The obtained porous carbon possesses an ultrahigh carbon yield of 56.9 wt.%, hierarchical pore structure, and multi-heteroatoms doping. It can still reach up to 244.7 F g-1 even loaded 20 mg of active material. In addition, the (NH4 )2 SO4 /agar gel electrolyte is synthesized, and the fabricated flexible ammonium ion capacitor exhibits a superior energy density of 40.8 Wh kg-1 . This work uncovers a new way to construct porous carbon, which is expected to synthesize more carbon materials using other carbon sources.

Flexible Aqueous Supercapacitors for Long Cycle-Life Using Electrode with Multiple Active C═S Sites.

Even though a few organic materials have attracted considerable attention for energy storage applications, their dissolution in the electrolyte during the charging-discharging processes presents a formidable challenge to their long-term performance. In this work, according to the principle of like dissolves like, non-polar trithiocyanuric acid (TCA) can effectively inhibit dissolution in an aqueous electrolyte, hence prolonging the cycle life. Moreover, theoretical calculations suggest that TCA lowers lowest unoccupied molecular orbital (LUMO) energy level, thereby promoting reaction kinetics. The CV curves of TCA maintain a rectangular structure even at a high scan rate of 1000 mV s‒1 and exhibit a remarkable capacitance retention rate of 93.1% after 50,000 cycles. Asymmetric flexible supercapacitors utilizing the TCA exhibit an impressive energy density. Moreover, they maintain 94.2% of their capacitance after undergoing 80,000 cycles. Their integration with perovskite solar cells to facilitate the rapid storage of photogenerated charges enables efficient solar energy utilization, providing a practical solution for capturing and storing renewable energy.

Large-Area Fabrication of Porous Graphene Networks on Carbon Fabric via Millisecond Photothermal Processing of Polyaniline for Supercapacitors.

Supercapacitors demonstrate promising potential for flexible, multi-functional energy storage devices; however, their widespread adoption is confronted by fabrication challenges. To access a combination of desirable device qualities such as flexibility, lightweight, structural stability, and enhanced electrochemical performance, carbon fiber (CF) can be utilized as a current collector, alongside graphene as an electrochemically active material. Yet achieving a cost-effective, large-scale graphene production, particularly on CF, remains challenging. Here, a rapid (<1 min) photothermal approach is developed for the large-scale production of graphene directly onto CF, utilizing polyaniline (PANI) as a polymer precursor. The in situ electropolymerization of PANI on CF facilitates its rapid synthesis on large areas, followed by conversion into graphene networks, enabling the binder-free fabrication of supercapacitor devices. These devices exhibit an areal capacitance of 180 mF cm-2 (at 2 mA cm-2 in 1 m H2SO4), an order of magnitude higher than other fabric-based devices. Moreover, the devised photothermal strategy allows for one-step preparation of supercapacitor devices on areas exceeding 100 cm-2, yielding an absolute areal capacitance of 4.5 F. The proportional increase in capacitance with device area facilitates scaling and indicates the commercial viability of this approach for low-cost, energy-efficient, and high-throughput production of lightweight, high-performance graphene-based multi-functional supercapacitor devices.

Modulating Electrochemical Energy Storage and Multi-Spectra Defense of MXenes by Interfacial Dual-Filler Engineering.

MXenes have attracted growing interest in electrochemical energy storage owing to their high electronic conductivity and editable surface chemistry. Besides, rendering MXenes with spectrum defense properties further broadens their versatile applications. However, the development of MXenes suffers from weak van der Waal interaction-driven self-restacking that leads to random alignment and inferior interface microenvironments. Herein, a nacre-inspired MXene film is tailored by dual-filling of 2-ureido-4[1H]-pyrimidinone (UPy)-modified polyvinyl alcohol (PVA-UPy) and carbon nanotubes (CNTs). The dual-nanofillers engineering endows the nanocomposite film with a highly ordered structure (a Herman's order value of 0.838), a high mechanical strength (139.5 MPa), and continuous conductive pathways of both the ab plane and c-axis. As a proof-of-concept, the tailored nanocomposite film achieves a considerable capacitance of 508.2 F cm-3 and long-term cycling stability without performance degradation for 10 000 cycles. It is efficient for spectra defense in radar and infrared bands, displaying a high electromagnetic shielding capacity (19186 dB cm2 g-1) and a super-low infrared (IR) emissivity (0.16), with negligible performance decay after saving in the air for 1 year, responsible for the applications in specific and complex conditions. This interfacial dual-filler engineering concept showcases effective nanotechnology toward sustainable energy applications with a long lifetime and safety.

In Situ Polymerization of Hydrogel Electrolyte on Electrodes Enabling the Flexible All-Hydrogel Supercapacitors with Low-Temperature Adaptability.

All-hydrogel supercapacitors are emerging as promising power sources for next-generation wearable electronics due to their intrinsic mechanical flexibility, eco-friendliness, and enhanced safety. However, the insufficient interfacial adhesion between the electrode and electrolyte and the frozen hydrogel matrices at subzero temperatures largely limit the practical applications of all-hydrogel supercapacitors. Here, an all-hydrogel supercapacitor is reported with robust interfacial contact and anti-freezing property, fabricated by in situ polymerizing hydrogel electrolyte onto hydrogel electrodes. The robust interfacial adhesion is developed by the synergistic effect of a tough hydrogel matrix and topological entanglements. Meanwhile, the incorporation of zinc chloride (ZnCl2) in the hydrogel electrolyte prevents the freezing of water solvents and endows the all-hydrogel supercapacitor with mechanical flexibility and fatigue resistance across a wide temperature range of 20 °C to -60 °C. Such all-hydrogel supercapacitor demonstrates satisfactory low-temperature electrochemical performance, delivering a high energy density of 11 mWh cm-2 and excellent cycling stability with a capacitance retention of 90% over 10000 cycles at -40 °C. Notably, the fabricated all-hydrogel supercapacitor can endure dynamic deformations and operate well under 2000 tension cycles even at -40 °C, without experiencing delamination and electrochemical failure. This work offers a promising strategy for flexible energy storage devices with low-temperature adaptability.

In Situ Construction of NiCoMn-LDH Derived from Zeolitic Imidazolate Framework on Eggshell-Like Carbon Skeleton for High-Performance Flexible Supercapacitors.

Active compounds based on LDH (ternary layered double hydroxide) are considered the perfect supercapacitor electrode materials on account of their superior electrochemical qualities and distinct structural characteristics, and flexible supercapacitors are an ideal option as an energy source for wearable electronics. However, the prevalent aggregation effect of LDH materials results in significantly compromised actual specific capacitance, which limits its broad practical applications. In this research, a 3D eggshell-like interconnected porous carbon (IPC) framework with confinement and isolation capability is designed and synthesized by using glucose as the carbon source to disperse the LDH active material and enhance the conductivity of the composite material. Second, by constructing NiCoMn-LDH nanocage structure based on ZIF-67 (zeolitic imidazolate framework-67) at the nanometer scale the obtained IPC/NiCoMn-LDH electrode material can expose more active sites, which allows to achieve excellent specific capacitance (2236 F g-1/ 310.6 mAh g-1 at 1 A g-1), good rate as well as the desired cycle stability (85.9% of the initial capacitance upon 5000 cycles test). The constructed IPC/NiCoMn-LDH//IPC ASC (asymmetric supercapacitor) exhibits superior capacitive property (135 F g-1/60.1 mAh g-1 at 0.5 A g-1) as well as desired energy density (40 Wh kg-1 at 800 W kg-1).

Super-Elastic and Temperature-Tolerant Hydrogel Electrodes for Supercapacitors via MXene Enhanced Ice-Templating Synthesis.

Developing flexible energy storage devices with good deformation resistance under extreme operating conditions is highly desirable yet remains very challenging. Super-elastic MXene-enhanced polyvinyl alcohol/polyaniline (AMPH) hydrogel electrodes are designed and synthesized through vertical gradient ice templating-induced polymerization. This approach allows for the unidirectional growth of polyaniline (PANI) and 2D MXene layers along the elongated arrayed ice crystals in a controlled manner. The resulting 3D unidirectional AMPH hydrogel exhibits inherent stretchability and electronic conductivity, with the ability to completely recover its shape even under extreme conditions, such as 500% tensile strain, 50% compressive strain. The presence of MXene in the hydrogel electrode enhances its resilience to mechanical compression and stretching, resulting in less variation in resistance. AMPH has a specific capacitance of 130.68 and 88.02 mF cm-2 at a current density of 0.2 and 2 mA cm-2, respectively, and retains 90% and 70% of its original capacitance at elongation of 100% and 200%, respectively. AMPH-based supercapacitors demonstrate exceptional performance in high salinity environments and wide temperature ranges (-30-80 °C). The high electrochemical activity, temperature tolerance, and mechanical robustness of AMPH-based supercapacitor endow it promising as the power supply for flexible and wearable electronic devices.

Conductive MXene/Polymer Composites for Transparent Flexible Supercapacitors.

Transparent flexible energy storage devices are limited by the trade-off among flexibility, transparency, and charge storage capability of their electrode materials. Conductive polymers are intrinsically flexible, but limited by small capacitance. Pseudocapacitive MXene provides high capacitance, yet their opaque and brittle nature hinders their flexibility and transparency. Herein, the development of synergistically interacting conductive polymer Ti3C2Tx MXene/PEDOT:PSS composites is reported for transparent flexible all-solid-state supercapacitors, with an outstanding areal capacitance of 3.1 mF cm-2, a high optical transparency of 61.6%, and excellent flexibility and durability. The high capacitance and high transparency of the devices stem from the uniform and thorough blending of PEDOT:PSS and Ti3C2Tx, which is associated with the formation of O─H…O H-bonds in the composites. The conductive MXene/polymer composite electrodes demonstrate a rational means to achieve high-capacity, transparent and flexible supercapacitors in an easy and scalable manner.