Ginkgo Leaf-Derived Carbon Supports for the Immobilization of Iron/Iron Phosphide Nanospheres for Electrocatalytic Hydrogen Evolution

Iron/iron phosphide nanospheres supported on ginkgo leaf-derived carbon (Fe&FeP@gl-C) are prepared using a post-phosphidation approach, with varying amounts of iron (Fe). The activity of the catalysts in the hydrogen evolution reaction (HER) outperforms iron/iron carbide nanospheres supported on ginkgo leaf-derived carbon (Fe&FexC@gl-C), due to enhanced work function, electron transfer, and Volmer processes. The d-band centers of Fe&FeP@gl-C-15 move away from the Fermi level, lowering the H2 desorption energy and accelerating the Heyrovsky reaction. Density functional theory (DFT) calculations reveal that the hydrogen-binding free energy |ΔGH*| value is close to zero for the Fe&FeP@gl-C-15 catalyst, showing a good balance between Volmer and Heyrovsky processes. The Fe&FeP@gl-C-15 catalyst shows excellent hydrogen evolution performance in 0.5 m H2SO4, driving a current density of 10 mA cm-2 at an overpotential of 92 mV. Notably, the Fe&FeP@gl-C-15 catalyst outperforms a 20 wt% Pt/C catalyst, with a smaller overpotential required to drive a higher current density above 375 mA cm-2.

Designed Synthesis and Electrochemical Performance Regulation of the Hierarchical Hollow Structure Cu2S/Cu7S4/NC Anode for Hybrid Supercapacitors

Copper-based compounds have attracted increasing attention as electrode materials for rechargeable devices, but their poor conductivity and insufficient stability inhibit their further development. Herein, an effective method has been proposed to improve the electrochemical properties of the copper-based electrodes by coating carbon materials and generating unique micro/nanostructures. The prepared Cu2S/Cu7S4/NC with hierarchical hollow structure possesses excellent electrochemical performance, attributing to the composition and structure optimization. The superior charge storage performance has been assessed by theoretical and experimental research. Specifically, the Cu2S/Cu7S4/NC exhibits remarkably higher electrical conductivity and lower adsorption-free energy for O* and OH* than those of Cu2O. Moreover, the Cu2S/Cu7S4/NC delivers a high specific capacitance of 1261.3 F·g-1 at the current density of 1 A·g-1 and also has great rate performance at higher current densities, which are much better than those of the Cu2O nanocubes. In addition, the assembled hybrid supercapacitor using Cu2S/Cu7S4/NC as the anode exhibits great energy density, power density, and cycling stability. This study has proposed a novel and feasible method for the synthesis of high-performance copper-based electrodes and their electrochemical performance regulation, which is of great significance for the advancement of high-quality electrode materials and rechargeable devices.

Waste Tire Heat Treatment to Prepare Sulfur Self-Doped Char: Operando Insight into Activation Mechanisms Based on the Char Structures Evolution

Waste tire (WT) can be heat-treated to be high-quality sulfur self-doped char via pyrolysis and K2FeO4-assisted activation processes. This work aimed at further studying the activation mechanisms based on the char structures evolution by operando experimental method. Activation treatment process (from 50 °C to 800 °C and then held for 3 h) was divided into six typical stages (S1–S6) and consisted of carbonization process (S1–S4) and effective activation process (S4–S6). During the carbonization process, the specific capacitance only increased from 0.2 F/g to 12.4 F/g, aromatic ring systems and alkyl-aryl C-C bonds generated, S 2p3/2 (sulphide bridge) was mainly gradually consumed. During the effective activation process, the specific capacitance hugely increased from 12.4 F/g to 112.5 F/g, aromatic ring systems and alkyl-aryl C-C bonds turned to ordered graphitic char. The pores massively generated from S4 to S5, while micropores partly formed to larger and mesopores+macropores fractionally converting to smaller from S5 to S6. Besides, both S 2p3/2 and S 2p5/2 (sulphone bridge) were enriched after S5. Furthermore, the key structural parameters for huge improvement of specific capacitance were found and it further revealed that mesopores+macropores possessed stronger promotion effect than micropores and S 2p3/2 was more beneficial than S 2p5/2.

Vitreum Etching-Assisted Fabrication of Porous Hollow Carbon Architectures for Enhanced Capacitive Sodium and Potassium-Ion Storage

Carbonaceous materials exhibit promising application in electrochemical energy storage especially for hollow or porous structure due to the fascinating and outstanding properties. Although there has been achieved good progress, controllable synthesis of hollow or porous carbons with uniform morphology by a green and easy way is still a challenge. Herein, a new artful and green approach is designed to controllably prepare hollow porous carbon materials with the assistance of boron oxide vitreum under a relatively low temperature of 500 °C. The vitreous B₂ O₃ provides a flowing carbonization environment and acts as etching agent accompanying with boron doping. By this general strategy, hollow and porous carbon architectures with various morphology of spheres and hollow polyhedrons are successfully fabricated by metal organic framework (MOF) precursors. Furthermore, such hollow carbon materials exhibit considerably excellent Na⁺ /K⁺ storage properties through enhanced capacitive behavior due to due to the highly porous structure and large surface area. It is notable that hollow carbon spheres display nearly 90% initial Coulombic efficiency, outstanding rate capability with 130 mAh g^-1 at 30 A g^-1 and long cycling life for sodium ion storage.

Waste tire heat treatment to prepare sulfur self-doped char via pyrolysis and K2FeO4-assisted activation methods

Waste tire was heat-treated to prepare sulfur self-doped chars via pyrolysis and activation processes. Pyrolytic waste tire chars were activated at different temperatures (600 °C, 800 °C, 1000 °C, and 1200 °C) with K₂FeO₄ additive ratios (mass ratio of K₂FeO₄ to char) being 0.5, 1, 2, and 3, respectively. The effective activation occurred over 600 °C with K₂FeO₄ additive ratios over 0.5. The strongest activation occurred at 1000 °C with K₂FeO₄ additive ratio of 3, and the specific capacitance increased to 129.5 F/g at 1 A/g, which was six times higher than that without K₂FeO₄. The activation mechanism revealed that higher K₂FeO₄ additive ratio promoted the transformation of large aromatic ring systems (≥6 rings) to small ones and smaller pores formation. When K₂FeO₄ additive ratio was less than 2, high ratio not only promoted alkyl-aryl C-C bonds formation, but also inhibited sulfur enrichment with S 2p_3/2 (sulphide bridge) converting to S 2p_5/2 (sulphone bridge). But when the ratio was further increased, slight decomposition of alkyl-aryl C-C bonds with the promoted conversion of S 2p_5/2 to S 2p_3/2 was witnessed. Furthermore, higher activation temperature promoted the conversion of aromatic ring systems and alkyl-aryl C-C bonds to form ordered graphitic structures. S 2p_3/2 was enriched before 800 °C, but both S 2p_3/2 and S 2p_5/2 were released at higher temperature. Formation of smaller pores was promoted before 1000 °C, but the char structure was then destroyed to form larger pores when temperature was further increased.

In situ activation graphitization to fabricate hierarchical porous graphitic carbon for supercapacitor

In situ activation–graphitization method based on the atomically dispersed K and Fe in organic salts is developed to synthesize hierarchical porous graphitic carbon by directly pyrolysis potassium citrate and iron citrate. Moreover, (NH₄)₂C₂O₄ is also employed as both N dopant and porogen to open up internal structure and regulate pore structure. The inside-out activation leads to the homogeneous reaction and interconnected hierarchical porous structure with few dead pores. Accompanied by high specific surface area, appropriate pore distribution, good conductivity, and N/O functional groups, the sample exhibits high capacitance of 322.6 F g⁻¹ at 0.5 A g⁻¹, good rate capability, and excellent cycling stability with 101.5% capacitance retention after 15,000 cycles. The supercapacitor shows an energy density of 21.3 W h kg⁻¹ at 456.7 W kg⁻¹ in 1 M Na₂SO₄. Easy synthesis, cost-effective, and environmentally benign, the work provides a promising strategy to produce hierarchical porous graphitic carbon applied in energy storage.

Production of novel carbon nanostructures by electrochemical reduction of polychlorinated organic rings under mild conditions for supercapacitors

Here, new carbon-based nanostructures were prepared via a one-step electrochemical method using hexagonal and pentagonal polychlorinated organic rings as the carbon source.

Activation of persulfate by nanoscale zero-valent iron loaded porous graphitized biochar for the removal of 17β-estradiol: Synthesis, performance and mechanism

In this work, the porosity, graphitization and iron doping of biochar were realized simultaneously by the pyrolysis of biomass and potassium ferrate (K₂FeO₄), then the iron-doped graphitized biochar was reduced to synthesize nanoscale zero-valent iron loaded porous graphitized biochar (nZVI/PGBC). 17β-estradiol (E2) is an environmental endocrine disruptor that can cause great harm to the environment in small doses. Experiments illustrated that nZVI/PGBC (100 mg/L) could completely remove E2 (3 mg/L) within 45 min by activating sodium persulfate (PS, 400 mg/L). The E2 removal efficiency of nZVI/PGBC was obviously superior to that of pristine biochar (BC), iron-doped graphitized biochar (Fe/GBC), nanoscale zero-valent iron (nZVI) and porous graphitized biochar (PGBC). The removal efficiency could be affected by reaction conditions, including reaction temperature, acidity, dosage of catalyst and oxidant and water matrix. Quenching experiments and electron spin resonance (ESR) demonstrated that SO₄^-· and HO were both responsible for E2 degradation. This study indicated that Fe⁰ and Fe²⁺ were the main catalytic active substances, while the catalytic ability of PGBC was not obvious. The reaction mechanism was proposed, that is, PS was activated by electrons provided by the redox reaction between Fe²⁺ and Fe³⁺, and PGBC acted as the carrier of nZVI, the adsorbent of E2 and the mediator of electron-transfer. This study demonstrates that nZVI/PGBC can be used as an effective activator for PS to remove organic pollutants in water.

Sulfur self-doped char with high specific capacitance derived from waste tire: Effects of pyrolysis temperature

Preparation of sulfur self-doped char derived from waste tire (WT) was realized via two successively processes of pyrolysis and activation treatment. WT was firstly pyrolyzed at 400 °C, 600 °C, 800 °C, and 1000 °C to collect waste tire chars (WTCs) and they were subsequently activated at 800 °C with potassium ferrate (K₂FeO₄). The specific capacitance of activated waste tire chars at different pyrolysis temperatures (AWTCs-x-800) decreased from 92.60 F/g to 54.05 F/g at 1 A/g with pyrolysis temperature rising from 400 °C to 1000 °C. As for AWTCs-x-800, higher pyrolysis temperature promoted pore-forming process before 800 °C, and higher pyrolysis temperature enlarged pores after 800 °C. Increase of pyrolysis temperature promoted decomposition of alkyl-aryl CC bonds, transformation of relative small to large aromatic ring system, ordered arrangement of carbon atoms. Besides, it was found that sulfur doping content dominated in specific capacitance performance before 800 °C while surface area dominated after 800 °C. The large surface area and high S 2p_3/2 (-C-S-C-, sulphide bridge) content were beneficial for the larger specific capacitance while more S 2p_5/2 (-C-SOx-C- (x = 2-4, sulphone bridge) had the negative effect. Pyrolysis mainly affected sulfur doping properties, lower pyrolysis temperature promoted sulfur enrichment and S 2p_3/2 generation. Activation promoted surface area improvement and sulfur conversion, higher pyrolysis temperature promoted surface area improvement and sulfur release before 800 °C while the promotion effects weakened after 800 °C, and sulfur transformation of S 2p_3/2 converting to S 2p_5/2 strengthened at higher pyrolysis temperature.

Microwave-Assisted Hydrothermal Preparation of Corn Straw Hydrochar as Supercapacitor Electrode Materials

In this work, we propose the microwave-assisted hydrothermal activation method to synthesize supercapacitor electrode materials from corn straw under a small amount of the potassium catalyst (30 wt %), which can meet the environmental protection and low-cost requirement. With the extension of radiation time from 40 to 100 min, the pore structure of hydrochar expands from the micropore to hierarchical pore, and the microstructure evolves from an amorphous structure to graphene-like sheets. Microwave-assisted hydrothermal activation can control the synergistic development of hierarchical pore and graphene-like sheets of hydrochar under the condition of using a lesser amount of the catalyst. The as-obtained HTC-40/70/100 shows an excellent graphitization degree and the developed hierarchical pores. By comparing the electrochemical performance of the symmetrical capacitor devices composed of corn straw hydrochar and pyrochar in organic electrolytes, we have found that the hydrochar is suitable for organic system symmetric capacitance, and the pore structure and graphitization degree are closely related to the transmission of ions and electrons in the electrolyte. Therefore, HTC-100 with a high specific surface area (1781 m²/g) and highly ordered microstructure has the best electrochemical performance.

Preparation of Highly Porous Graphitic Activated Carbon as Electrode Materials for Supercapacitors by Hydrothermal Pretreatment-Assisted Chemical Activation

The obstruction of traditional chemical activation lies in the addition of excessive catalysts to prepare the highly porous graphitic activated carbon (HPGAC), we propose the hydrothermal pretreatment-assisted chemical activation method to synthesize HPGAC as electrode materials using a small amount of Na-based catalysts (20 wt %). Hydrolysis accompanied by the strong depolymerization and reorganization of the coal framework is beneficial to the removal of different kinds of oxygen-containing structures (including cross-linking bonds, functional groups, and heterocycles) from lignite; thus, the deoxidization effect of hydrothermal carbonization (HTC) on hydrochar gradually strengthens with the increase in pretreatment temperature from 180 to 300 °C, resulting in the formation of a lot of disordered nanostructures and a smooth and compact surface. In the subsequent chemical activation stage, the microstructure of hydrochar is beneficial to the formation of a lot of graphene-like sheets and developed micropores even under a small amount of Na-based catalysts (20 wt %). The as-obtained C-HTC-300 with a highly ordered microstructure and a high specific surface area (S BET) of 1945.33 m2/g has an excellent electrochemical performance. Compared with a large consumption of catalyst for synthesizing HPGAC in traditional chemical activation, the hydrothermal pretreatment-assisted method meets the environmental protection and low-cost preparation requirements.

Coal-based 3D hierarchical porous carbon aerogels for high performance and super-long life supercapacitors

Coal-based 3D hierarchical porous carbon aerogels (3D HPCAs) has been successfully fabricated from a freeze-drying method and with subsequent of calcination process, using coal oxide as carbon precursors, and PVA as both cross-linking agent and sacrifice template. The 3D HPCAs, using as electrode materials for supercapacitors, display outstanding electrochemical performance. The optimal sample (HPCAs-0.4-800) presents a high specific capacitance of 260 F g-1 at 1 A g-1, and exhibits considerable rate capability with the retention of 81% at 10 A g-1. Notably, HPCAs-0.4-800 shows an excellent cycling stability with 105% of the capacitance retention after 50000 cycles at 10 A g-1, attributing to its unique hierarchical porosity, high surface area up to 1303 m2 g-1, and improved conductivity. This work offers a promising route to synthesize coal-based porous carbon aerogels electrode materials for supercapacitors.

Biomass-based Hierarchical Porous Carbon for Supercapacitors: Effect of Aqueous and Organic Electrolytes on the Electrochemical Performance

Biomass-based hierarchical porous carbon (SCPC) exhibits excellent electrochemical performance in electric double layer capacitors, prepared by carbonization and activation of straw cellulose. To investigate the potential applications of SCPC in supercapacitors, the effect of aqueous and organic electrolytes on the electrochemical performance of SCPC was studied in detail. In H₂ SO₄ , the SCPC electrode exhibits higher specific capacitance (358 F g^-1 ) and outstanding cycling stability with 95.6 % capacitance retention over 10 000 cycles. The SCPC electrode shows superior rate capability with 90.7 % capacitance retention in KOH, and higher energy density of 17.9 Wh kg^-1 in Na₂ SO₄ . The SCPC electrode exhibits ideal capacitance characteristics, superior rate capability with capacitance retention of 95.8 %, and high energy density of 36.0 Wh kg^-1 in tetraethylammonium tetrafluoroborate/propylene carbonate (Et₄ NBF₄ /PC). The significant difference of capacitive performance of SCPC electrode in various electrolytes is mainly attributed to the difference in the electrolyte ion size, ionic conductivity, matching between the electrolyte ions and pore structure, and matching between anions and cations adsorbed on the positive and negative electrodes. This work not only establishes the relationship between the structure of SCPC and its electrochemical performance in different electrolytes, but also provides a reference for the high value-added utilization of SCPC.

Highly Porous Graphitic Activated Carbons from Lignite via Microwave Pretreatment and Iron-Catalyzed Graphitization at Low-Temperature for Supercapacitor Electrode Materials

At present, the preparation of highly porous graphitic activated carbons (HPGACs) using the usual physical and chemical activation methods has met a bottleneck. In this study, HPGACs are directly synthesized from lignite at 900 °C. The whole process is completed by a microwave pretreatment, a graphitization conversion of the carbon framework at a low temperature using a small amount of FeCl3 (10–30 wt%), and a subsequent physical activation using CO2. Consequently, the dispersed and mobile iron species, in the absence of oxygen functional groups (removed during the microwave pretreatment), can greatly promote catalytic graphitization during pyrolysis, and, as an activating catalyst, can further facilitate the porosity development during activation. The as-obtained AC-2FeHLH-5-41.4(H) presents a low defect density, high purity, and specific surface area of 1852.43 m2 g−1, which is far greater than the AC-HLH-5-55.6(H) obtained solely by physical activation. AC-2FeHLH-5-41.4(H) as a supercapacitor electrode presents an excellent performance in the further electrochemical measurements. Such a convenient and practical method with low cost proves a scalable method to prepare HPGACs from a wide range of coal/biomass materials for industrial scale-up and applications.

Biomass-Derived Porous Carbon-Based Nanostructures for Microwave Absorption

Currently, electromagnetic (EM) pollution poses severe complication toward the operation of electronic devices and biological systems. To this end, it is pertinent to develop novel microwave absorbers through compositional and structural design. Porous carbon (PC) materials demonstrate great potential in EM wave absorption due to their ultralow density, large surface area, and excellent dielectric loss ability. However, the large-scale production of PC materials through low-cost and simple synthetic route is a challenge. Deriving PC materials through biomass sources is a sustainable, ubiquitous, and low-cost method, which comes with many desired features, such as hierarchical texture, periodic pattern, and some unique nanoarchitecture. Using the bio-inspired microstructure to manufacture PC materials in mild condition is desirable. In this review, we summarize the EM wave absorption application of biomass-derived PC materials from optimizing structure and designing composition. The corresponding synthetic mechanisms and development prospects are discussed as well. The perspective in this field is given at the end of the article.

Rapid microwave activation of waste palm into hierarchical porous carbons for supercapacitors using biochars from different carbonization temperatures as catalysts

A rapid, simple and cost-effective approach to prepare hierarchical porous carbons (PCs) for supercapacitors is reported by microwave activation of abundant and low-cost waste palm, biochar (BC) and KOH. BCs from waste palm at different carbonization temperatures (300–700 °C), as catalysts and microwave receptors, were used here for the first time to facilitate the conversion of waste palm into hierarchical PCs. As a result, the high-graphitization PC obtained at a BC carbonization temperature of 300 °C (PC-300) possessed a high surface area (1755 m² g⁻¹), a high pore volume (0.942 cm³ g⁻¹) and a moderate mesoporosity (37.79%). Besides their high-graphitization and hierarchical porous structure, the oxygen doping in PC-300 can also promote the rapid transport of electrolyte ions. The symmetric supercapacitor based on the PC-300 even in PVA/LiCl gel electrolyte exhibited a high specific capacitance of 164.8 F g⁻¹ at a current density of 0.5 A g⁻¹ and retained a specific capacitance of 121.3 F g⁻¹ at 10 A g⁻¹, demonstrating a superior rate capacity of 73.6%. Additionally, the PC-300 supercapacitor delivered a high energy density of 14.6 W h kg⁻¹ at a power density of 398.9 W kg⁻¹ and maintained an energy density of 10.8 W h kg⁻¹ at a high power density of 8016.5 W kg⁻¹, as well as an excellent cycling stability after 2000 cycles with a capacitance retention of 92.06%.

A rapid, simple and cost-effective approach to prepare hierarchical porous carbons (PCs) for supercapacitors is reported by microwave activation of abundant and low-cost waste palm, biochar (BC) and KOH.

One-Pot Template-Free Strategy toward 3D Hierarchical Porous Nitrogen-Doped Carbon Framework in Situ Armored Homogeneous NiO Nanoparticles for High-Performance Asymmetric Supercapacitors

The composites based on graphitic carbon and transitional metal oxides are regarded as one of the most promising electrochemical materials owing to the synergistic combination of the advantages of both superior electrical conductivity and high pseudocapacitance. In this work, a simple one-pot template-free strategy for the preparation of three-dimensional hierarchical porous nitrogen-doped carbon framework in situ armored NiO nanograins (NCF/NiO) by an ammonia-induced method assisted by the pyrolysis of a decomposable salt is reported. Due to such unique architecture and homogeneously dispersed nanoparticles, the as-prepared NCF/NiO-2 hybrid exhibits a large specific surface area (412.3 m² g^-1), a high specific capacitance (1074 F g^-1 at 1 A g^-1), good rate capability (820 F g^-1 at 20 A g^-1), and outstanding cycling performance (almost no decay after 5000 cycles). Moreover, the solid-state asymmetric supercapacitor, assembled with NCF/NiO-2 and NCS electrodes, can achieve a high cell potential of 1.6 V and deliver a superior specific capacitance of 113 F g^-1 at 1 A g^-1 with a maximum energy density of 40.18 W h kg^-1 at a power density of 800 W kg^-1, consequently, giving rise to stable cycling performance (94.3% retention over 5000 cycles). The prepared devices are shown to power 20 green light-emitting diodes efficiently. These encouraging results open up a wide horizon for developing novel carbon-supported metal oxide electrode materials for high rate energy conversion and storage devices.

Chemical Foaming Coupled Self-Etching: A Multiscale Processing Strategy for Ultrahigh-Surface-Area Carbon Aerogels

Due to the unique structure, carbon aerogels have always shown great potential for multifunctional applications. At present, it is highly desirable but remains challenging to tailor the microstructures with respect to porosity and specific surface area to further expand its significance. A facile chemical foaming coupled self-etching strategy is developed for multiscale processing of carbon aerogels. The strategy is directly realized via the pyrolysis of a multifunctional precursor (pentaerythritol melamine phosphate) without any special drying process and multiple steps. In the micrometer scale, the macroporous scaffold structures with interconnected and strutted carbon nanosheets are built up by chemical foaming from decomposition of melamine, whereas the meso/microporous nanosheets are formed via self-etching by phosphorus-containing species. The delicately hierarchical structures and record-breaking specific surface area of 2668.4 m² g^-1 render the obtained carbon aerogels great potentials for absorption (324.1-593.6 g g^-1 of absorption capacities for varied organic solvents) and energy storage (338 F g^-1 of specific capacitance). The construction of such novel carbon nanoarchitecture will also shed light on the design and synthesis of multifunctional materials.

Extraordinary Porous Few-Layer Carbons of High Capacitance from Pechini Combustion of Magnesium Nitrate Gel

Highly capacitive carbons are viewed as promising commercial materials for supercapacitors, but few species satisfy the requirements of high capacitance and low cost. Here, we demonstrate an extraordinary porous few-layer carbon by facile Pechini combustion of magnesium nitrate gel, which combined salicylic acid as a complexing agent with magnesium nitrate as an inorganic metal salt. The as-synthesized carbon material delivers a capacitance of 415 F g^-1, mostly stemming from a large specific surface area (∼1312 m² g^-1), a fluent channel for transport of the electrolyte, as well as electrochemical redox reactions at O,N-associated active sites. Such porous few-layer carbons may accelerate the adoption of carbon-based supercapacitors for commercial high-power energy storage applications.

Graphitic porous carbon: efficient synthesis by a combustion method and application as a highly selective biosensor

Efficient synthesis of graphitic porous carbon by combustion method for the simultaneous determination of uric acid and dopamine.

Monolithic Cu/C hybrid beads with well-developed porosity for the reduction of 4-nitrophenol to 4-aminophenol

Cu/C hybrid beads with well-developed porosity, offering potential advantages of low cost, an environmentally friendly fabrication process, easy processing and durable activity, were successfully fabricated.