Synthesis of porous carbon material based on biomass derived from hibiscus sabdariffa fruits as active electrodes for high-performance symmetric supercapacitors

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.

Screen-Printed Stretchable Supercapacitors Based on Tin Sulfide-Decorated Face-Mask-Derived Activated Carbon Electrodes with High Areal Energy Density

In this work, tin sulfide nanosheets decorated on face-mask-derived activated carbon have been explored as electrode material for electrochemical supercapacitors. A hydrothermal route was employed to grow tin sulfide on the surface and inside of high-surface-area face-mask-derived activated carbon, activated at 850 °C, to produce a hierarchical interconnected porous composite (ACFM-850/TS) structure. The presence of tin sulfide in the porous carbon framework exposed the surface active sites for rapid adsorption/desorption of electrolyte ions and ensured high utilization of the porous carbon surface. Furthermore, the porous ACFM-850 framework prevented the stacking/agglomeration of tin sulfide sheets, thereby enhancing the charge-transport kinetics in the composite electrodes. Benefiting from the synergistic effect of tin sulfide and ACFM-850, the resulting ACFM-850/TS composite exhibited an attractive specific capacitance of 423 F g-1 at a 0.5 A g-1 current density and superior rate capability (71.3% at a 30 A g-1 current density) in a 1.0 M Na2SO4 electrolyte. In addition, we fabricated a planar symmetric interdigitated supercapacitor on a stretchable Spandex fabric using an ACFM-850/TS composite electrode and carboxymethyl cellulose/NaClO4 as a solid-state gel electrolyte employing a scalable screen-printing process. The as-prepared stretchable supercapacitors displayed an ultrahigh energy density of 9.2 μWh cm-2 at a power density of 0.13 mW cm-2. In addition, they exhibited an excellent cyclic stability of 64% even after 10,000 charge-discharge cycles and 42% after 1000 continuous stretch (at 25% stretching)/release cycles. Such screen-printed interdigitated planar supercapacitors with activated carbon composite electrodes and a solid-state gel electrolyte act as promising low-cost energy-storage devices for wearable and flexible integrated electronic devices.

Scalable slot-die coated flexible supercapacitors from upcycled PET face shields

Upcycling Covid19 plastic waste into valuable carbonaceous materials for energy storage applications is a sustainable and green approach to minimize the burden of waste plastic on the environment. Herein, we developed a facile single step activation technique for producing activated carbon consisting of spherical flower like carbon nanosheets and amorphous porous flakes from used PET [poly(ethylene terephthalate)] face shields for supercapacitor applications. The as-obtained activated carbon exhibited a high specific surface area of 1571 m2 g-1 and pore volume of 1.64 cm3 g-1. The specific capacitance of these carbon nanostructure-coated stainless steel electrodes reached 228.2 F g-1 at 1 A g-1 current density with excellent charge transport features and good rate capability in 1 M Na2SO4 aqueous electrolyte. We explored the slot-die coating technique for large-area coatings of flexible high-performance activated carbon electrodes with special emphasis on optimizing binder concentration. Significant improvement in electrochemical performance was achieved for the electrodes with 15 wt% Nafion concentration. The flexible supercapacitors fabricated using these electrodes showed high energy and power density of 21.8 W h kg-1 and 20 600 W kg-1 respectively, and retained 96.2% of the initial capacitance after 10 000 cycles at 2 A g-1 current density. The present study provides a promising sustainable approach for upcycling PET plastic waste for large area printable supercapacitors.

Preparation and Electrochemical Performance of Bio-Oil-Derived Hydrochar as a Supercapacitor Electrode Material

The rapid consumption of fossil energy and the urgent demand for sustainable development have significantly promoted worldwide efforts to explore new technology for energy conversion and storage. Carbon-based supercapacitors have received increasing attention. The use of biomass and waste as a carbon precursor is environmentally friendly and economical. In this study, hydrothermal pretreatment was used to synthetize coke from bio-oil, which can create a honeycomb-like structure that is advantageous for electrolyte transport. Furthermore, hydrothermal pretreatment, which is low in temperature, can create a low graphitization degree which can make heteroatom introduction and activation easier. Then, urea and KOH were used for doping and activation, which can improve conductivity and capacitance. Compared with no heteroatom and activation hydrothermal char (HC) (58.3 F/g at 1 A/g), the prepared carbon material nitrogen doping activated hydrothermal carbon (NAHC1) had a good electrochemical performance of 225.4 F/g at 1 A/g. The specific capacitance of the prepared NAHC1 was improved by 3.8 times compared with that of HC.

Three‐dimensional nanoporous activated carbon electrode derived from acacia wood for high‐performance supercapacitor

Herein, the novel acacia wood based hierarchical porous activated carbons (AWCs) are easily prepared, low cost and have excellent characterization, such as special biomass nanopores via structural stability and large specific surface areas. Activating agents such as KOH, ZnCl2, and H3PO4 have been used to convert acacia wood carbon into active carbons such as AWC-K, AWC-Z, and AWC-P, respectively, which are named after the activating agent. As a supercapacitor electrode, the AWC-K sample has a high yield was 69.8%, significant specific surface area of 1563.43 m2g−1 and layer thickness of 4.6 mm. Besides that, it showed specific capacitance of 224.92 F g−1 at 0.5 A g−1 in 2 M KOH as electrolyte. In addition, the AWC-K//AWC-K symmetrical supercapacitor device displays high energy density of 23.98 Wh kg−1 at 450 W kg−1 power density with excellent cycling number stability was 93.2% long lifetime of 10,000 cycles using 0.5 M Na2SO4 as electrolyte. The high electrochemistry performance mainly contributed the special biomass pores structure. Therefore, the presented approach opens new avenues in supercapacitor applications to meet energy storage.

Carboxylated graphene oxide nanosheets as efficient electrodes for high-performance supercapacitors

In the presence of dry ice, a series of graphitic materials with carboxylated edges (ECGs) were synthesized by ball milling graphite for varied times (24, 36, and 46 h). The influence of carboxylation on the physiochemical characteristics and electrochemical performance as effective electrodes for supercapacitors were assessed and compared with pure graphite. Several characterization techniques were employed to investigate into the morphology, texture, microstructure, and modification of the materials. Due to its interconnected micro-mesoporous carbon network, which is vital for fast charge-discharge at high current densities, storing static charges, facilitating electrolyte transport and diffusion, and having excellent rate performance, the ECG-46 electrode among the investigated samples achieved the highest specific capacitance of 223 F g−1 at 0.25 A g−1 current density and an outstanding cycle stability, with capacitance retention of 90.8% for up to 10,000 cycles. Furthermore, the symmetric supercapacitor device based on the ECG-46 showed a high energy density of 19.20 W h kg−1 at 450.00 W kg−1 power density. With these unique features, ball milling of graphitic material in dry ice represents a promising approach to realize porous graphitic material with oxygen functionalities as active electrodes.

Highly active N, S Co-Doped Ultramicroporous Carbon for High-Performance Supercapacitor Electrodes

N, S-doped ultramicroporous carbons (NSUC-x) with a high nitrogen/sulfur content and a narrow pore-size distribution of around 0.55 nm were firstly prepared using L-cysteine as a nitrogen and sulfur source. The phase, graphitization degree, morphology, specific surface area, pore structure and surface condition of NSUC-x are investigated to analyze the key role in electrochemical performance. Such an ultramicroporous structure and N, S doping not merely provide a high-specific surface area and a suitable pore size, but also induce a good wettability for the fast transport and adsorption of electrolyte ions. Due to the above strategies, the typical NSUC-0.4 exhibits a high gravimetric capacitance of 339 F g⁻¹ at 0.5 A g⁻¹ as well as a capacity retention of 91.6% after 10,000 cycles in a three-electrode system using a 6 M KOH electrolyte. More attractively, a NSUC-0.4-assembled symmetrical supercapacitor delivers an energy output of 7.4 Wh kg⁻¹ at 100 W kg⁻¹ in 6 M KOH as well as a capacity retention of 92.4% after 10,000 cycles, indicating its practical application prospect. Our findings open up new prospects for the design and electrochemical application of N, S-doped ultramicroporous carbons.

Highly dispersed RuO2-biomass carbon composite made by immobilization of ruthenium and dissolution of coconut meat with octyl ammonium salicylate ionic liquid for high performance flexible supercapacitor

Poor dispersion of metal oxide-biomass carbon composite limits its further improvement in electrochemical properties. The study reports synthesis of highly dispersed RuO₂-biomass carbon nanocomposite (HD-RuO₂-BC). Octyl ammonium salicylate ionic liquid was combined with Ru³⁺ ion to form Ru-based ionic liquid. Followed by addition of coconut meat, microwave treatment to form homogeneous solution, thermal reduction in N₂ and oxidation in air in sequence. The resulting HD-RuO₂-BC shows three-dimensional architecture and high Ru loading of 9.2%. RuO₂ nanoparticles of 6.2 nm were uniformly dispersed in biomass carbon sheets. Excellent dispersion and small size of RuO₂ nanoparticles achieve to a significant synergy between RuO₂ and biomass carbon. HD-RuO₂-BC electrode gives high capacitance of 907.7 F g^-1 at 1 A g^-1. The value is more than that of BC (150.6 F g^-1) and RuO₂ electrodes (584.7 F g^-1), verifying that introduction of RuO₂ achieves to an obviously enhanced capacitance. The symmetrical flexible supercapacitor exhibits excellent supercapacitor performances, including high capacitance (403.8 F g^-1 at 1.0 A g^-1), rate-capacity (223.1 F g^-1 at 50 A g^-1), cycling stability (98.2% capacity retention after 10,000 cycles at 50 A g^-1) and energy density (378.7 Wh Kg^-1at power density of 5199.2 W kg^-1).

Functional utilization of biochar derived from Tenebrio molitor feces for CO2 capture and supercapacitor applications

Biochar has attracted great interest in both CO2 capture and supercapacitor applications due to its unique physicochemical properties and low cost.

Low content Ru-incorporated Pd nanowires for bifunctional electrocatalysis

This paper reports the facile synthesis and characterization of carbon supported Pd nanowires with low Ru contents (nRuPd/C). An anti-galvanic replacement reaction involving the reduction of Ru(iii) ions by nanoporous Pd nanowires to form nRuPd alloy nanowires was observed. A series of nRuPd/C materials with various Ru/Pd ratios were prepared by the spontaneous deposition of a Ru cluster on a Pd nanowire core using different Ru precursor concentrations (RuCl₃ = 0.5, 1.0, 5.0 mM). The successful formation of low content Ru-incorporated Pd nanowires without individual Ru clusters were confirmed using physicochemical characterization. The electrocatalytic activity of the nRuPd/C for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in alkaline media was measured by RDE polarization experiments. The electrocatalytic activity varied greatly depending on the Ru content on the Pd nanowires. Among the catalysts, the prepared Pd nanowires incorporated with a very small amount of Ru (ca. 1.4 wt%) exhibited excellent electrocatalytic activity toward the ORR and HER: positive ORR/HER onset and E_1/2 potentials, higher n value, and lower Tafel slope.

The catalytic activity of Pd nanowires with low Ru contents showed superior bifunctional electrocatalytic performance towards both ORR and HER compared to the benchmarking Pt/C.