Extraordinary Thickness-Independent Electrochemical Energy Storage Enabled by Cross-Linked Microporous Carbon Nanosheets

Friendly Environmental Strategies to Recycle Zinc-Carbon Batteries for Excellent Gel Polymer Electrolyte (PVA-ZnSO4-H2SO4) and Carbon Materials for Symmetrical Solid-State Supercapacitors

In this report, we introduce a novel idea to prepare a redox additive in a gel polymer electrolyte system of PVA-ZnSO4-H2SO4 based on zinc-carbon battery recycling. Here, zinc cans from spent zinc-carbon batteries are dissolved completely in 1 M H2SO4 to obtain a redox additive in an aqueous electrolyte of ZnSO4-H2SO4. Moreover, carbon nanoparticles and graphene nanosheets were synthesized from carbon rod and carbon powder from spent zinc-carbon batteries by only one step of washing and electrochemical exfoliation, respectively, which have good electrochemical capability. The three-electrode system using a ZnSO4-H2SO4 electrolyte with carbon nanoparticles and graphene nanosheets as working electrodes shows high electrochemical adaptability, which points out its promising application in supercapacitor devices. Thus, the symmetrical solid-state supercapacitor devices based on the sandwich structure of graphene nanosheets/PVA-ZnSO4-H2SO4/graphene nanosheets illustrated the highest energy density of 39.17 W h kg-1 at a power density of 1700 W kg-1. While symmetrical devices based on carbon nanoparticles/PVA-ZnSO4-H2SO4/carbon nanoparticles exhibited a maximum energy density of 35.65 W h kg-1 at a power density of 1700 W kg-1. Moreover, these devices illustrate strong durability after 5000 cycles, with approximately 90.2% and 73.1% remaining, respectively. These results provide a promising strategy for almost completely recycling zinc-carbon batteries, one of the most popular dry batteries.

Zinc-Carbon Battery Recycling for Investigating Carbon Materials for Supercapacitor Applications

In this paper, carbon materials, including graphene nanosheets and carbon nanoparticles, were prepared from spent zinc-carbon batteries by the following two simple methods: electrochemical exfoliation and ultrasonication. Here, graphene nanosheets were synthesized by electrochemical exfoliation in 0.5 M H2SO4 by using a direct current power supply with two carbon rods from spent zinc-carbon batteries. Carbon nanoparticles were prepared by fast ultrasonication in a low-cost, green solution of DI water and ethanol. Graphene nanosheets in this study have high quality, large scale, and good electrochemical ability, while carbon nanoparticles have a unique nanosize and a good specific surface area. These carbon materials were applied for electrochemical measurements for supercapacitor studies and showed excellent stability at different temperatures. Moreover, electric double-layer capacitor devices based on graphene nanosheets and carbon nanoparticles were also used in electrochemical studies with strong stability and good electrochemical capability.

Utilization of carbon-based nanomaterials for wastewater treatment and biogas enhancement: A state-of-the-art review

The management of environmental pollution and carbon dioxide (CO2) emissions is a challenge that has spurred increased research interest in determining sustainable alternatives to decrease biowaste. This state-of-the-art review aimed to describe the preparation and utilization of carbon-based nanomaterials (CNM) for biogas enhancement and wastewater contaminant (dyes, color, and dust particles) removal. The novelty of this review is that we elucidated that the performance of CNMs in the anaerobic digestion (AD) varies from one system to another. In addition, this review revealed that increasing the pyrolysis temperature can facilitate the transition from one CNM type to another and outlined the methods that can be used to develop CNMs, including arc discharge, chemical exfoliation, and laser ablation. In addition, this study showed that methane (CH4) yield can be slightly increased (e.g. from 33.6% to 60.89%) depending on certain CNM factors, including its type, concentration, and feedstock. Temperature is a fundamental factor involved in the method and carbon sources used for CNM synthesis. This review determined that graphene oxide is not a good additive for biogas and CH4 yield improvement compared with other types of CNM, such as graphene and carbon nanotubes. The efficacy of CNMs in wastewater treatment depends on the temperature and pH of the solution. Therefore, CNMs are good adsorbents for wastewater contaminant removal and are a promising alternative for CO2 emissions reduction. Further research is necessary to determine the relationship between CNM synthesis and preparation costs while accounting for other factors such as gas flow, feedstock, consumption time, and energy consumption.

High Mass-Loading Biomass-Based Porous Carbon Electrodes for Supercapacitors: Review and Perspectives

Biomass-based porous carbon (BPC) with renewability and flexible nano/microstructure tunability has attracted increasing attention as efficient and cheap electrode materials for supercapacitors. To meet commercial needs, high mass-loading electrodes with high areal capacitance are preferred when designing supercapacitors. The increased mass percentage of active materials can effectively improve the energy density of supercapacitors. However, as the thickness of the electrode increases, it will face the following challenges including severely blocked ion transport channels, poor charging dynamics, poor electrode structural stability, and complex preparation processes. A bridge between theoretical research and practical applications of BPC electrodes for supercapacitors needs to be established. In this review, the advances of high mass-loading BPC electrodes for supercapacitors are summarized based on different biomass precursors. The key performance evaluation parameters of the high mass-loading electrodes are analyzed, and the performance influencing factors are systematically discussed, including specific surface area, pore structure, electrical conductivity, and surface functional groups. Subsequently, the promising optimization strategies for high mass-loading electrodes are summarized, including the structure regulation of electrode materials and the optimization of other supercapacitor components. Finally, the major challenges and opportunities of high mass-loading BPC electrodes in the future are discussed and outlined.

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.

Boosting capacitive performance of N, S co-doped hierarchical porous lignin-derived carbon via self-assembly assisted template-coupled activation

Heteroatom-doped porous carbon materials show promise for use as supercapacitor electrodes, but the tradeoff between surface area and the heteroatom dopant levels limits the supercapacitive performance. Here, we modulated the pore structure and surface dopants of N, S co-doped hierarchical porous lignin-derived carbon (NS-HPLC-K) via self-assembly assisted template-coupled activation. The ingenious assembly of lignin micelles and sulfomethylated melamine into a magnesium carbonate basic template greatly promoted the KOH activation process, which endowed the NS-HPLC-K with uniform distributions of activated N/S dopants and highly accessible nanosized pores. The optimized NS-HPLC-K exhibited a three-dimensional hierarchically porous architecture composed of wrinkled nanosheets and a high specific surface area of 2538.3 ± 9.5 m²/g with a rational N content of 3.19 ± 0.01 at.%, which boosted the electrical double-layer capacitance and pseudocapacitance. Consequently, the NS-HPLC-K supercapacitor electrode delivered a superior gravimetric capacitance of 393 F/g at 0.5 A/g. Furthermore, the assembled coin-type supercapacitor showed good energy-power characteristics and cycling stability. This work provides a novel idea for designing eco-friendly porous carbons for use in advanced supercapacitors.

A hierarchical integrated 3D carbon electrode derived from gingko leaves via hydrothermal carbonization of H3PO4 for high-performance supercapacitors

Electrochemical ultracapacitors derived from green and sustainable materials could demonstrate superior energy output and an ultra-long cycle life owing to large accessible surface area and obviously shortened ion diffusion pathways. Herein, we have established an efficient strategy to fabricate porous carbon (GLAC) from sustainable gingko leaf precursors by a facile hydrothermal activation of H3PO4 and low-cost pyrolysis. In this way, GLAC with a hierarchically porous structure exhibits extraordinary adaptability toward a high energy/power supercapacitor (∼709 F g-1 at 1 A g-1) in an aqueous electrolyte (1 M KOH). Notably, the GLAC-2-based supercapacitor displays an ultra-high stability of ∼98.24% even after 10 000 cycles (10 A g-1) and an impressive energy density as large as ∼71 W h kg-1 at a power density of 1.2 kW kg-1. The results provide new insights that the facile synthetic procedure coupled with the excellent performance contributes to great potential for future application in the electrochemical energy storage field.

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.

Multifunctional applications for waste zinc-carbon battery to synthesize carbon dots and symmetrical solid-state supercapacitors

In this study, we provide a simple and green approach to recycle waste zinc carbon batteries for making carbon dots and porous carbon material. The carbon dots are easily synthesized by one green step, the hydrothermal treatment of a carbon rod in a mixture of DI water and pure ethanol to obtain a blue fluorescence under UV light, which can be used directly as a fluorescence ink. The as-prepared carbon dot process give typical dots with a uniform diameter from 3 to 8 nm with a strong slight blue fluorescent. The porous carbon material is also recycled from carbon powder in a waste battery via one green step annealing process without any chemical activation and with a hierarchically porous structure. This porous carbon material is demonstrated as an electrode for symmetrical solid state supercapacitors (SSCs) in a sandwich structure: porous carbon/PVA-KOH/porous carbon. The SSCs using recycled porous carbon electrodes exhibit a good energy density of 4.58 W h kg-1 at a power density of 375 W kg-1 and 97.6% retention after 2000 cycles. The facile one green step of hydrothermal and also that of calcination provide a promising strategy to recycle waste zinc carbon batteries, which transfers the excellent applications.

Demulsification of water-in-crude oil emulsion driven by a carbonaceous demulsifier from natural rice husks

Removing emulsified water from a water-in-crude oil (W/O) emulsion is critically required prior to downstream processing in the petroleum industry. In this work, environmentally friendly and amphipathic rice husk carbon (RHC) demulsifier was prepared by a simple carbonization process in a muffle furnace using rice husks as starting materials. RHC was characterized by field-emission scanning electron microscope, energy dispersive spectrometer, Fourier transform infrared spectrometer, ultraviolet-visible spectrometer, powder X-ray diffraction, zeta potential and synchronal thermal analyzer. The factors such as dosage, temperature, settling time, pH value and salinity were systematically investigated. The results indicated that the dehydration efficiency (DE) reached as high as 96.99% with 600 mg/L of RHC for 80 min at 70 °C. RHC exhibited an optimal DE under neutral condition, but it was also effective under acidic and alkaline conditions. Also, it had an excellent salt tolerance. The possible demulsification mechanism was explored by interfacial properties, different treatment methods for RHC and microexamination. The demulsification of RHC is attributed to its high interfacial activity, oxygen-containing groups and content of silica. It indicates that RHC is an effective demulsifier for the treatment of the W/O emulsion.

A Low-Temperature Dehydration Carbon-Fixation Strategy for Lignocellulose-Based Hierarchical Porous Carbon for Supercapacitors

Lignocellulose-based hierarchical porous carbon is a very promising electrode material for supercapacitors, but lower volumetric energy density and yield have hindered its practical applications. Herein, a low-temperature dehydration carbon-fixation method using NH₄ Cl as modification reagent was developed to prepare rice husk-based hierarchical porous carbon (RHPC) with high volumetric performance and yield. The RHPC-N electrode exhibited a higher volumetric specific capacitance of 134.4 F cm^-3 than that of the RHPC electrode (98.4 F cm^-3 ) in 1 m Et₄ NBF₄ /propylene carbonate electrolyte. The volumetric energy density (28.8 Wh L^-1 ) of the RHPC-N electrode was 37.1 % higher than that of the RHPC electrode (21.0 Wh L^-1 ), which greatly enhanced the practical application potential of RHPC in supercapacitors. Moreover, the yield of RHPC increased 1.2 times by this method, which greatly improved the production capacity and reduced the cost. This research establishes a simple and highly efficient method to improve the volumetric energy density and the yield of lignocellulose-based hierarchical porous carbon.

High performance supercapacitors based on wood-derived thick carbon electrodes synthesized via green activation process

A green, versatile, and universal H2O2 activation method is proposed to improve the capacitive properties of high-mass loading wood-based supercapacitors.

TiO2/Chlorophyll S-Scheme Composite Photocatalyst with Improved Photocatalytic Bactericidal Performance

Step-scheme (S-scheme) photocatalysts have been proposed for highly efficient charge separation and strong redox activity in the photocatalysis field. Here, we reported a facile strategy to obtain the S-scheme heterojunction composite TiO₂/chlorophyll (Chl). The S-scheme heterojunction enables the significant improvement of electron transfer efficiency at the interfacial heterojunction of TiO₂/Chl. Also, the lifted conduction band and valence band of TiO₂/Chl resulted in more than 1.61 times generation of reactive oxidizing species, compared to that of bare TiO₂. In addition, TiO₂/Chl was applied as a photocatalytic bactericidal material to fabricate commercial masks for prolonged life span of the mask. The TiO₂/Chl-coated mask filter exhibited excellent bactericidal effect on Escherichia coli under light illumination (2.94 × 10⁷ cfu E. coli were killed by 1 cm^-2 coated mask filters within illumination of 3 h), while commercial mask filters showed no bactericidal effect. After three circulation-sterilization tests, the TiO₂/Chl-made mask filter maintained the initial bactericidal effect, which greatly extended the life span of the mask that presents a promising strategy to alleviate the supply stress of masks.

Multilayer graphene in situ formed in carbonized waste paper with the synergism of nickel and sodium

MLG is in situ formed with the synergism of nickel and sodium. The porous structure of amorphous carbon is effectively optimized with the formation of MLG and its capacitive performance is clearly improved.

Non-tubular-biomass-derived nitrogen-doped carbon microtubes for ultrahigh-area-capacity lithium-ion batteries

The ever-increasing electric vehicles and portable electronics make lithium-ion barreries (LIBs) toward high energy density, resulting in long driving range and standby times. Generally, excellent electrochemical performance can be obtained in thin electrode materials with low mass loadings (<1 mg cm^-2), but it is difficult to be achieved in commercial electrodes with high mass loadings (>10 mg cm^-2). In this work, we report a facile method for fabricating nitrogen doped carbon microtubes (N-CMTs) consisted of crumped carbon nanosheets for high-performance LIBs with ultrahigh mass loading, where non-tubular biomass waste (i.e., peanut dregs) is employed as the precursor. Benefiting from the hollow tubular conductive network, high graphitization, and hierarchical structure, the as-synthesized N-CMTs exhibit ultrahigh area capacity of 6.27 mAh cm^-2 at a current density of 1.5 mA cm^-2 with a high mass loading of 15 mg cm^-2 and superior cycling stability for LIBs. Our approach provides an effective strategy for the preparation of nitrogen-doped carbon microtubes to develope high energy LIBs with high mass loading electrodes.

Facile self-templating synthesis of heteroatom-doped 3D porous carbon materials from waste biomass for supercapacitors

Heteroatom-doped 3D porous carbon has been synthesized by utilizing hydroxyapatite in pig bones as a self-template and used in symmetric supercapacitors exhibiting ultra-high energy density both in an aqueous electrolyte and organic electrolyte.