Microphase Separation Engineering toward 3D Porous Carbon Assembled from Nanosheets for Flexible All-Solid-State Supercapacitors

Phosphorescent Elastomer through Carbon Nanodots Microphase Engineering for Diverse Applications

Stretchable phosphorescent elastomers possess great potential in flexible devices and wearable electronics. However, traditional room-temperature phosphorescent (RTP) materials exhibit poor stretchability, thereby presenting a challenge in reconciling the contradiction between RTP performance and stretchability. Here, we present carbon nanodots (CNDs) microphase engineering strategy that integrates CNDs with rigid microconfinement within a flexible matrix, demonstrating phosphorescent elastomers with high performance. The resultant elastomers exhibit a maximum stretchability of up to 97% and a phosphorescence lifetime of up to 1119 ms. Subsequently, the universality of this approach is further demonstrated by tuning the phosphorescence wavelength across the visible-light range. These elastomers maintain stable optical properties under diverse and complex conditions. Potential applications, including 3D art, anticounterfeiting, and flexible displays, showcase the versatility of this design. This work provides a new pathway for designing stretchable phosphorescent elastomers and expands the application potential of phosphorescent materials.

Recent Progress of Flexible Solid-State Supercapacitors: Electrodes, Electrolytes and Practical Application

Flexible solid-state supercapacitors (FSSCs) have garnered significant attention due to their advantages, including lightness, adaptability, enhanced safety, and extensive operational potential windows. These features make them highly suitable as energy storage devices for the next generation of portable and flexible electronics. The recent surge in the development and remarkable breakthroughs in novel wearable electronics have further propelled research into FSSCs. Nevertheless, several pressing issues need to be addressed in this field, including synthesizing flexible electrode materials with superior electrochemical energy storage capabilities, enhancing the physicochemical properties of solid gel polymer electrolytes, particularly in extreme environments, and ensuring effective contact between electrodes and gel electrolytes. This paper presents an overview of the latest advancements in FSSCs, focusing on electrode materials and electrolytes. Additionally, it delves into the current challenges and future prospects of FSSCs.

Chitosan-based high-performance flexible supercapacitor via "in-situ co-doping/self-regulation-activation" strategy

The construction of N, P co-doped hierarchically porous carbons (NPHPC) by a facile and green approach is crucial for high-performance energy storage but still an enormous challenge. Herein, an environment-friendly "in-situ co-doping, self-regulation-activation" strategy is presented to one-pot synthesize NPHPC using a phytic acid-induced polyethyleneimine/chitosan gel (PEI-PA-CS) as single precursor. NPHPC displayed a specific surface area of up to 1494 m2 g-1, high specific capacitance of 449 F g-1 at 1 A g-1, outstanding rate capability and cycling durability in a wide temperature range (-20 to 60 °C). NPHPC and PEI-PA-CS electrolyte assembled symmetric quasi-solid-state flexible supercapacitor presents superb energy outputs of 27.06 Wh kg-1 at power density of 225 W kg-1. For capacitive deionization (CDI), NPHPC also exhibit an excellent salt adsorption capacity of 16.54 mg g-1 in 500 mg L-1 NaCl solution at a voltage of 1.4 V, and regeneration performance. This study provides a valuable reference for the rational design and synthesis of novel biomass-derived energy-storage materials by integrating phytic acid induced heteroatom doping and pore engineering.

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.

Ammonium Folate-Reinforced Self-Assembly of Gelatin into N/B/O-Enriched Hierarchical Porous Carbons with Loosely Layered Structure for Anti-Freezing Flexible Supercapacitors

Heteroatom-doped layered porous carbons are recently regarded as promising electrode materials for high energy density supercapacitors because they can integrate high-level heteroatom-doping and layered nano-space together to provide huge pseudocapacitive reaction areas and accelerate ion diffusion/transport. Herein, an innovative strategy is reported to prepare N/B/O co-doped layered porous carbons via ammonium folate-reinforced self-assembly of gelatin and boric acid followed by carbonization. Biomass-derived ammonium folate not only acts as an N-riched precursor but also can fasten in the process of self-assembly via boric acid-assisted electrostatic adsorption and hydrogen bonding to promote the formation of stable 3D cross-linked networks, resulting in the obtained N/B/O co-doped layered porous carbon (BNLC-850) has a large specific surface area (1822 m2 g-1 ), hierarchical porous structure and super-high heteroatom contents (N, 12.65; B, 5.67; and O, 13.84 at.%). The BNLC-850 achieves an ultrahigh specific capacitance of 525.2 F g-1 in the alkaline electrolyte at 0.5 A g-1 , meanwhile, DFT calculations reveal that the high-level N/B/O-doping can effectively weaken the adsorption barriers of K-ions. Moreover, the BNLC-850 assembles anti-freezing flexible solid-state supercapacitors in MPEI-TF-IL gel polymer electrolyte deliver a high energy density of 41.2 Wh kg-1 , excellent flexibility, and long cycle-life at -20 °C.

Amorphous carbon nanosheets suitable for deep eutectic solvent electrolyte toward cryogenic energy storage

The emerging deep eutectic solvent (DES) electrolyte has great potential in realizing commercial-scale application of electric double-layer capacitors (EDLCs) served in low temperature environment. That goal, however, rests with how to design the interface structure of electrode materials for well-matching with DES electrolyte. Herein, porous carbon nanosheets (PCNs) were obtained from coal tar pitch through Friedel-Crafts acylation reaction and melting salt intercalation process. The morphology, specific surface area and porosity of porous carbon nanosheets were regulated by tailoring the abundance of the dangling-bonds grafted on the CTP molecules. Profiting from the large specific surface area, suitable pore structure and good two-dimensional structure to provide more active sites and enhance ion transport capacity, the PCNs-0.10 delivers a maximal specific capacitance of 504F g-1 at 0.1 A g-1, which is overmatch than most of previously reported for other carbon materials. As-assembled symmetrical EDLCs using K+ DES electrolyte, can be assembled to work at -40 °C to 75 °C and exhibit satisfactory energy density. The strategy proposed here has opened a new way for exploring the large-scale preparation of electrode materials suitable for ultra-low temperature capacitors.

Evaluation of Polymer Gel Electrolytes for Use in MnO2 Symmetric Flexible Electrochemical Supercapacitors

Flexible electrochemical supercapacitors (FESCs) are emerging as innovative energy storage systems, characterized by their stable performance, long cycle life, and portability/foldability. Crucial components of FESCs, such as electrodes and efficient electrolytes, have become the focus of extensive research. Herein, we examine deep eutectic solvent (DES)-based polymer gel systems for their cost-effective accessibility, simple synthesis, excellent biocompatibility, and exceptional thermal and electrochemical stability. We used a mixture a DES, LiClO4-2-Oxazolidinone as the electroactive species, and a polymer, either polyvinyl alcohol (PVA) or polyacrylamide (PAAM) as a redox additive/plasticizer. This combination facilitates a unique ion-transport process, enhancing the overall electrochemical performance of the polymer gel electrolyte. We manufactured and used LiClO4-2-Oxazolidinone (LO), polyvinyl alcohol-LiClO4-2-Oxazolidinone (PVA-LO), and polyacrylamide-LiClO4-2-Oxazolidinone (PAAM-LO) electrolytes to synthesize an MnO2 symmetric FESC. To evaluate their performance, we analyzed the MnO2 symmetric FESC using various electrolytes with cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). The FESC featuring the PVA-LO electrolyte demonstrated superior electrochemical and mechanical performances. This solid-state MnO2 symmetric FESC exhibited a specific capacitance of 121.6 F/g within a potential window of 2.4 V. Due to the excellent ionic conductivity and the wide electrochemical operating voltage range of the PVA-LO electrolyte, a high energy density of 97.3 Wh/kg at 1200 W/kg, and a long-lasting energy storage system (89.7% capacitance retention after 5000 cycles of GCD at 2 A/g) are feasibly achieved. For practical applications, we employed the MnO2 symmetric FESCs with the PVA-LO electrolyte to power a digital watch and a light-emitting diode, further demonstrating their real-world utility.

Recent Advances in Porous Carbon Materials as Electrodes for Supercapacitors

Porous carbon materials have demonstrated exceptional performance in various energy and environment-related applications. Recently, research on supercapacitors has been steadily increasing, and porous carbon materials have emerged as the most significant electrode material for supercapacitors. Nonetheless, the high cost and potential for environmental pollution associated with the preparation process of porous carbon materials remain significant issues. This paper presents an overview of common methods for preparing porous carbon materials, including the carbon-activation method, hard-templating method, soft-templating method, sacrificial-templating method, and self-templating method. Additionally, we also review several emerging methods for the preparation of porous carbon materials, such as copolymer pyrolysis, carbohydrate self-activation, and laser scribing. We then categorise porous carbons based on their pore sizes and the presence or absence of heteroatom doping. Finally, we provide an overview of recent applications of porous carbon materials as electrodes for supercapacitors.

Oxygen-enriched lignin-derived porous carbon nanosheets promote Zn2+ storage

Carbon-based zinc-ion capacitors (ZICs) have sparked intense research enthusiasm because of large power density, good rate capability and cycling stability. However, there is still a long way to go before they achieve commercial applications. Herein, oxygen-enriched lignin-derived porous carbon nanosheets (OLCKs) were prepared by one-step carbonization-activation method, and more O-containing functional groups were generated on the surface of the porous carbon by post-surface functionalization strategy. The self-doped N can change the electron distribution of carbon skeleton and decrease energy barrier of chemical absorption of Zn²⁺/H⁺. Meanwhile, the carbonyl group can significantly enhance the wettability of OLCKs. Furthermore, the diffusion-controlled reactions mainly exist at high and low potential ranges in CV curves, which demonstrates the occurred Faradaic reaction. Consequently, the assembled aqueous ZICs based on OLCKs demonstrate a capacity of 121.7 mAh/g at 0.3 A/g, energy density of 94.3 Wh kg^-1 and good cyclic stability. Besides, the assembled Zn//PVA/LiCl/ZnCl₂(gel)//OLCK4 ZIC can also achieve energy density of 134.4 Wh kg^-1 at 0.1 A/g. This work provides a novel design strategy by incorporating abundant O and N-containing functional groups to enhance energy density.

Spatial Confinement Strategy for Micelle-Size-Mediated Modulation of Mesopores in Hierarchical Porous Carbon Nanosheets with an Efficient Capacitive Response

Commercial supercapacitors using available carbon products have long been criticized for the under-utilization of their prominent specific surface area (SSA). In terms of carbonaceous electrode optimization, excessive improvement in SSA observed in the gaseous atmosphere might have little effect on the final performance because cracked/inaccessible pore alleys considerably block the direct electrolyte ion transport in a practical electrochemical environment. Herein, mesopore-adjustable hierarchically porous carbon nanosheets are fabricated based on a micelle-size-mediated spatial confinement strategy. In this strategy, hydrophobic trimethylbenzene in different volumes of the solvent can mediate the interfacial assembly with a carbon precursor and porogen segment through π-π bonding and van der Waals interaction to yield micelles with good dispersity and the diameter varying from 119 to 30 nm. With an increasing solvent volume, the corresponding diffusion coefficient (3.1-14.3 m2 s-1) of as-obtained smaller micelles increases, which makes adjacent micelles gather rapidly and then grow along the radial direction of oligomer aggregates to eventually form mesopores on hierarchically porous carbon nanosheets (MNC150-4.5). Thanks to the pore-expansion effect of trimethylbenzene, the mesoporous volume can be adjusted from 28.8 to 40.0%. Mesopores on hierarchically porous carbon nanosheets endow MNC150-4.5 with an enhanced electrochemically active surface area of 819.5 m2 g-1, which gives rise to quick electrolyte accessibility and a correspondingly immediate capacitive response of 338 F g-1 at 0.5 A g-1 in a three-electrode system. Electrolyte transport through pathways within MNC150-4.5 ultimately enables the symmetric cell to deliver a high energy output of 50.4 Wh kg-1 at 625 W kg-1 in a 14 m LiOTF electrolyte and 95% capacitance retention after 100,000 cycles, which show its superior electrochemical performance over representative carbon-based supercapacitors with aqueous electrolytes in recent literature.