Effect of porosity enhancing agents on the electrochemical performance of high-energy ultracapacitor electrodes derived from peanut shell waste

Impact of trivalent Yttrium on the structural and optical properties of CaAl2O4: New frontier in supercapacitor positive electrode

In this work, trivalent Yttrium doped calcium aluminate (CaAl2O4:x% Y3+) were synthesized for the first time. Through Photoluminescence (PL) spectroscopy and Commission Internationale de l'Eclairage (CIE), CaAl2O4:0.1 % Y3+ has demonstrated to be a potential high emitting phosphor material amongst other high concentration Y3+ doped samples, emitting a vibrant blue - pink hue where others are emitting a transiting hue from blue to green within a white vertex region. FTIR and UV-Vis have confirmed the prepared material and the presence of Y dopant. The SEM showed insignificant morphological change and the presence of pores, which were quantified using BJH and DFT methods to be micro - and meso-pores. Moreover, CaAl2O4 is also being reported as a positive electrode in supercapacitors for the first time. The analysis shows that it has superior performance within 1 M KOH electrolyte, with a specific capacity of 47.71 mA h g-1 at 1 A g-1 and a maximum power of 39.68 kW kg-1. Trasatti's method showed a surface (138 Fg-1) and diffusion (695 Fg-1) contribution ratio of 17:83 (%) of the total stored energy. It has a capacity retention and columbic efficiency of 100 % at the end of 10 000 cycles, which was achieved via utilization of all micropores reaction sites. The EIS showed a small solution resistance of 0.75 Ω, indicating high ionic conductivity and a phase angle of - 50 ° . Thus, these results show that CaAl2O4 is a potential candidate for photoluminescence and energy storage application.

Microwave engineered NiZrO3@GNP as efficient electrode material for energy storage applications

Supercapacitors (SCs) have emerged as attractive energy storage devices due to their rapid charge/discharge rates, long cycle life, and high-power density. However, the development of innovative electrode materials to achieve high-performance remains crucial to meet future requirements in supercapacitor technology. In this work, we have explored the potential of a microwave-engineered NiZrO3@GNP composite as a promising electrode material for SCs. A microwave assisted hydrothermal approach was adopted for the fabrication of the NiZrO3@GNP nanocomposite. Structural and morphological investigations showed its structural richness and its chemical compositions. When applied as a SC electrode, this innovative combination exhibits battery-like behaviour with higher specific capacity (577.63 C g-1) with good cyclic stability, and good performance. We have assembled an asymmetric-type two-electrode SC device and analysed its electrochemical features. This NiZrO3@GNP device exhibits the specific capacity of 47 C g-1 with capacitance retention of 70% after 2000 charge-discharge cycles. Further research on optimizing the synthesis process and exploring different device configurations could pave the way for even higher-performance supercapacitors in the future.

High electrochemical performance of nickel cobaltite@biomass carbon composite (NiCoO@BC) derived from the bark of Anacardium occidentale for supercapacitor application

Biomass carbon-based materials are highly promising for supercapacitor (SC) electrodes due to their availability, environment-friendliness, and low cost. Herein, an easy energy-saving hydrothermal process was used to produce NiCo2O4/NiOOH (NiCoO) composites with biomass carbon (BC) derived from the bark of Anacardium occidentale (AO) at different synthesis time durations (2 h, 4 h, 8 h, 16 h). The structural and morphological properties of the samples were analysed using XRD, Raman spectroscopy, XPS, SEM, TEM and BET, and the results exhibit the presence of carbon inserted into the nickel-cobalt hydroxide matrix. The NiCoO@BC composite synthesized in 4 h (NiCoO@BC(4 h)) displays a good specific capacitance of 475 F g-1 at 0.5 A g-1 and a low equivalent series resistance (ESR) value of 0.36 Ω. It shows a good coulombic efficiency of 98% and retains 86% of the capacitance after 4000 cycles. The asymmetric supercapacitor (ASC) device (NiCoO@BC(4 h)//AC) assembled using activated carbon (AC) as a negative electrode displays 20 W h kg-1 energy density and 900 W kg-1 power density at 1 A g-1. The stability test shows a good coulombic efficiency of 99% and 78% capacitance retention after 15 000 cycles. These findings imply that NiCoO@BC composites have outstanding electrochemical properties, making them suitable as SC electrode materials.

Unveiling the Potential of Corn Cob Biochar: Analysis of Microstructure and Composition with Emphasis on Interaction with NO2

In the context of sustainable solutions, this study examines the pyrolysis process applied to corn cobs, with the aim of producing biochar and assessing its effectiveness in combating air pollution. In particular, it examines the influence of different pyrolysis temperatures on biochar properties. The results reveal a temperature-dependent trend in biochar yield, which peaks at 400 °C, accompanied by changes in elemental composition indicating increased stability and extended shelf life. In addition, high pyrolysis temperatures, above 400 °C, produce biochars with enlarged surfaces and improved pore structures. Notably, the highest pyrolysis temperature explored in this study is 600 °C, which significantly influences the observed properties of biochars. This study also explores the potential of biochar as an NO2 adsorbent, as identified by chemical interactions revealed by X-ray photoelectron spectroscopy (XPS) analysis. This research presents a promising and sustainable approach to tackling air pollution using corn cob biochar, providing insight into optimized production methods and its potential application as an effective NO2 adsorbent to improve air quality.

Biomass Hierarchical Porous Carbonized Typha angustifolia Prepared by Green Pore-Making Technology for Energy Storage

The cost-effective biomass-derived carbon with high electrochemical performance is highly desirable for the sustainable development of advanced energy storage devices. In this manuscript, Typha angustifolia with a large output and loose porous characteristics was selected as the raw material of biomass. In the synthesis process, KHCO₃, which is more environmentally friendly, is used as a pore-forming agent, and the low-cost, easy-to-clean fluxing agent NaCl is used to assist the pore-forming process. Based on the analysis of thermogravimetric-infrared test results, the calcination procedure of porous carbon was designed reasonably, so that the functions of the pore-forming agent and fluxing agent could be fully exerted. Its high electrochemical performance is attributed to combined contributions from high surface area and hierarchical porous structures. The as-prepared carbon also showed an outstanding capacitance of 317.2 F/g at a current density of 1 A g^-1 and a high capacitance retention of over 97.83% after 5000 cycles at a current density of 4 A g^-1. This work provides an outstanding renewable candidate and a feasible route design strategy for the fabrication of high-performance electrodes.

Preparation of highly efficient p-doped porous camellia shell-based activated carbon and its adsorption of carotenoids in camellia oil

The vegetable oil industry is limited by the high cost of the refining process, and the camellia shells (CS) are beneficial to the development of the industry as a biomass raw material for camellia oil decolorization. In this study, CS-based p-doped porous activated carbon (CSHAC) obtained after the pyrolysis of H3PO4-laden CS-hydrochar (CSH) was used for the adsorption of carotenoids in camellia oil. The results showed that the adsorption efficiency of CSHAC for carotenoids was 96.5% compared to 67–87% for commercial decolorizers, and exhibited a fast adsorption rate (20 min). The results of adsorption isotherms indicated that the adsorption of carotenoids on CSHAC occurred through a multi-layer process. Furthermore, the analysis of adsorption kinetics showed that the adsorption of carotenoids by CSHAC was a complex process involving physical and chemical reactions, and chemisorption was the dominant kinetic mechanism. This superior performance of CSHAC in adsorbing carotenoids was attributed to its micro-mesoporous structure, hydrophobicity, and numerous active sites.

Recent Advanced Supercapacitor: A Review of Storage Mechanisms, Electrode Materials, Modification, and Perspectives

In recent years, the development of energy storage devices has received much attention due to the increasing demand for renewable energy. Supercapacitors (SCs) have attracted considerable attention among various energy storage devices due to their high specific capacity, high power density, long cycle life, economic efficiency, environmental friendliness, high safety, and fast charge/discharge rates. SCs are devices that can store large amounts of electrical energy and release it quickly, making them ideal for use in a wide range of applications. They are often used in conjunction with batteries to provide a power boost when needed and can also be used as a standalone power source. They can be used in various potential applications, such as portable equipment, smart electronic systems, electric vehicles, and grid energy storage systems. There are a variety of materials that have been studied for use as SC electrodes, each with its advantages and limitations. The electrode material must have a high surface area to volume ratio to enable high energy storage densities. Additionally, the electrode material must be highly conductive to enable efficient charge transfer. Over the past several years, several novel materials have been developed which can be used to improve the capacitance of the SCs. This article reviews three types of SCs: electrochemical double-layer capacitors (EDLCs), pseudocapacitors, and hybrid supercapacitors, their respective development, energy storage mechanisms, and the latest research progress in material preparation and modification. In addition, it proposes potentially feasible solutions to the problems encountered during the development of supercapacitors and looks forward to the future development direction of SCs.

Impact of Thermally Reducing Temperature on Graphene Oxide Thin Films and Microsupercapacitor Performance

In this work, a thermally reduced graphene oxide (TRGO) thin film on microscopic glass was prepared using spray coating and atmospheric pressure chemical vapour deposition. The structure of TRGO was analysed using X-ray diffraction (XRD) spectroscopy, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, and ultraviolet–visible spectroscopy (UV-Vis) suggesting a decrease in oxygen functional groups (OFGs), leading to the restacking, change in colour, and transparency of the graphene sheets. Raman spectrum deconvolution detailed the film’s parameters, such as the crystallite size, degree of defect, degree of amorphousness, and type of defect. The electrochemical performance of the microsupercapacitor (µ-SC) showed a rectangular cyclic voltammetry shape, which was maintained at a high scan rate, revealing phenomenal electric double-layer capacitor (EDLC) behaviour. The power law and Trasatti’s analysis indicated that low-temperature TRGO µ-SC is dominated by diffusion-controlled behaviour, while higher temperature TRGO µ-SC is dominated by surface-controlled behaviour.

Electrocatalytic water oxidation performance in an extended porous organic framework with a covalent alliance of distinct Ru sites

The rational synthesis of durable, earth-abundant efficient electrocatalysts for the oxygen evolution reaction (OER) from water is one of the most important routes for storing renewable energy and minimizing fossil fuel combustion. The prime hurdles for effectively utilizing commercial RuO₂ as (OER) electrocatalysts are its very low stability, catalyst deactivation, and high cost. In this work, we explored a Ru-integrated porous organic polymer (Ru@Bpy-POP) by a facile one-pot Friedel-Crafts alkylation strategy between redox-active (Ru(demob)3Cl2) and a carbazole unit, which is composed of unique features including an extended framework unit, isolated active sites, and tunable electrode kinetics. Ru@Bpy-POP can serve as a bridge between a Metal-Organic Framework (MOF) and POP-based catalytic systems with a balanced combination of covalent bonds (structural stability) and open metal sites (single site catalysis). Ru@Bpy-POP, deposited on a three-dimensional nickel foam electrode support, exhibits a promising electrocatalytic OER activity with an ultra-low ruthenium loading compared to a benchmark RuO₂ catalyst, providing an overpotential of about 270 mV to reach 10 mA cm^-2 in an alkaline medium. Moreover, a high current density of 248 mA cm^-2 was achieved for the Ru@Bpy-POP catalyst at only 1.6 V (vs. RHE), which is much higher than 91 mA cm^-2 for commercial RuO₂. The robust, albeit highly conjugated, POP framework not only triggered facile electro-kinetics but also suppressed aggregation and metallic corrosion during electrolysis. In particular, the benefits of covalent integration of distinct Ru sites into the framework can modulate intermediate adsorption and charge density, which contributes to its exceptional OER activity. All of the critical steps involved in OER are complemented by Density Functional Theory (DFT) calculations, which suggest that electrocatalytic water oxidation proceeds from a closed-shell configuration to open-shell electronic configurations with high-spin states. These open-shell configurations are more stable than their closed-shell counterparts by 1 eV, improving the overall catalytic activity.

Ion accumulation-induced capacitance elevation in a microporous graphene-based supercapacitor

High-performance porous 3D graphene-based supercapacitors are one of the most promising and challenging directions for future energy technologies. Microporous graphene has been synthesized by the pyrolysis method. The fabricated lightweight graphene with a few layers (FLG) has an ultra-high surface area of 2266 m² g⁻¹ along with various-sized micropores. The defect-induced morphology and pore size distribution of the fabricated graphene are examined, and the results show that the micropores vary from 0.85 to 1.9 nm and the 1.02 nm pores contribute 30% of the total surface area. The electrochemical behaviour of the electrode fabricated using this graphene has been studied with various concentrations of the KOH electrolyte. The highest specific capacitance of the graphene electrode of 540 F g⁻¹ (close to the theoretical value, ∼550 F g⁻¹) can be achieved by using the 1 M KOH electrolyte. This high specific capacitance contribution involves the counter ion adsorption, co-ion desorption, and ion permutation mechanisms. The formation of a Helmholtz layer, as well as the diffusion of the electrolyte ions, confirms this phenomenon. The symmetrical solid-state supercapacitor fabricated with the graphene electrodes and PVA–KOH gel as the electrolyte exhibits excellent energy and power densities of 18 W h kg⁻¹ and 10.2 kW kg⁻¹, respectively. This supercapacitor also shows a superior 100% coulombic efficiency after 6000 cycles.

High-performance porous 3D graphene-based supercapacitors are one of the most promising and challenging directions for future energy technologies.

Bio-Derived Carbon with Tailored Hierarchical Pore Structures and Ultra-High Specific Surface Area for Superior and Advanced Supercapacitors

We report here on a hollow-fiber hierarchical porous carbon exhibiting an ultra-high specific surface area, synthesized by a facile method of carbonization and activation, using the Metaplexis Japonica (MJ) shell. The Metaplexis Japonica-based activated carbon demonstrated a very high specific surface area of 3635 m² g^-1. Correspondingly, the derived carbonaceous material delivers an ultra-high capacitance and superb cycle life in an alkaline electrolyte. The pore-ion size compatibility is optimized using tailored hierarchical porous carbon and different ion sized organic electrolytes. In ionic liquids nonaqueous based electrolytes we tailored the MJ carbon pore structure to the electrolyte ion size. The corresponding supercapacitor shows a superior rate performance and low impedance, and the device records specific energy and specific power densities as high as 76 Wh kg^-1 and 6521 W kg^-1, as well as a pronounced cycling durability in the ionic liquid electrolytes. Overall, we suggest a protocol for promising carbonaceous electrode materials enabling superior supercapacitors performance.

Binary vanadium pentoxide carbon-graphene foam composites derived from dark red hibiscus sabdariffa for advanced asymmetric supercapacitor

The development of advanced electrode materials derived from biomass for the next generation of energy storage devices, such as supercapacitors with high specific energy and specific power coupled with a good cycle stability, is required to meet the high demand for electric vehicles and portable devices. In this study, sustainable binary vanadium pentoxide carbon-graphene foam composites (V₂O₅@C-R₂HS/GF) were synthesized using a solvothermal method. The X-ray diffraction, Raman and FTIR techniques were used to study the structural properties of the composites (V₂O₅@C-R₂HS/20 mg GF and V₂O₅@C-R₂HS/40 mg GF). The SEM micrographs displayed an accordion-like morphology resulting from the graphene foam-modified V₂O₅@C-R₂HS composite. The V₂O₅@C-R₂HS, V₂O₅@C-R₂HS/20 mg GF and V₂O₅@C-R₂HS/40 mg GF composites were evaluated in a three-electrode configuration using 6 M potassium hydroxide (KOH) as an aqueous electrolyte. Furthermore, a two-electrode device was carried out by fabricating an asymmetric device (V₂O₅@C-R₂HS/GF//AC) where V₂O₅@C-R₂HS/20 mg GF was used as a positive electrode and activated carbon (AC) as a negative electrode at a cell voltage of 1.6 V in 6 M KOH. The V₂O₅@C-R₂HS/GF//AC showed a high specific energy and specific power values of 55 W h kg^-1 and 707 W kg^-1, respectively, at a specific current of 1 A g^-1. The asymmetric device presented a good stability test showing 99% capacity retention up to 10 000 cycles and was confirmed by the floating time up to 150 h with specific energy increasing 23.6% after the first 10 h. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 2)'.

Novel Thermally Reduced Graphene Oxide Microsupercapacitor Fabricated via Mask-Free AxiDraw Direct Writing

We demonstrate a simple method to fabricate all solid state, thermally reduced graphene oxide (TRGO) microsupercapacitors (µ-SCs) prepared using the atmospheric pressure chemical vapor deposition (APCVD) and a mask-free axiDraw sketching apparatus. The Fourier transform infrared spectroscopy (FTIR) shows the extermination of oxygen functional groups as the reducing temperature (RT) increases, while the Raman shows the presence of the defect and graphitic peaks. The electrochemical performance of the µ-SCs showed cyclic voltammetry (CV) potential window of 0–0.8 V at various scan rates of 5–1000 mVs⁻¹ with a rectangular shape, depicting characteristics of electric double layer capacitor (EDLC) behavior. The µ-SC with 14 cm⁻² (number of digits per unit area) showed a 46% increment in capacitance from that of 6 cm⁻², which is also higher than the µ-SCs with 22 and 26 cm⁻². The TRGO-500 exhibits volumetric energy and power density of 14.61 mW h cm⁻³ and 142.67 mW cm⁻³, respectively. The electrochemical impedance spectroscopy (EIS) showed the decrease in the equivalent series resistance (ESR) as a function of RT due to reduction of the resistive functional groups present in the sample. Bode plot showed a phase angel of −85° for the TRGO-500 µ-SC device. The electrochemical performance of the µ-SC devices can be tuned by varying the RT, number of digits per unity area, and connection configuration (parallel or series).

Enhanced Electrochemical Behavior of Peanut-Shell Activated Carbon/Molybdenum Oxide/Molybdenum Carbide Ternary Composites

Biomass-waste activated carbon/molybdenum oxide/molybdenum carbide ternary composites are prepared using a facile in-situ pyrolysis process in argon ambient with varying mass ratios of ammonium molybdate tetrahydrate to porous peanut shell activated carbon (PAC). The formation of MoO2 and Mo2C nanostructures embedded in the porous carbon framework is confirmed by extensive structural characterization and elemental mapping analysis. The best composite when used as electrodes in a symmetric supercapacitor (PAC/MoO2/Mo2C-1//PAC/MoO2/Mo2C-1) exhibited a good cell capacitance of 115 F g-1 with an associated high specific energy of 51.8 W h kg-1, as well as a specific power of 0.9 kW kg-1 at a cell voltage of 1.8 V at 1 A g-1. Increasing the specific current to 20 A g-1 still showcased a device capable of delivering up to 30 W h kg-1 specific energy and 18 kW kg-1 of specific power. Additionally, with a great cycling stability, a 99.8% coulombic efficiency and capacitance retention of ~83% were recorded for over 25,000 galvanostatic charge-discharge cycles at 10 A g-1. The voltage holding test after a 160 h floating time resulted in increase of the specific capacitance from 74.7 to 90 F g-1 at 10 A g-1 for this storage device. The remarkable electrochemical performance is based on the synergistic effect of metal oxide/metal carbide (MoO2/Mo2C) with the interconnected porous carbon. The PAC/MoO2/Mo2C ternary composites highlight promising Mo-based electrode materials suitable for high-performance energy storage. Explicitly, this work also demonstrates a simple and sustainable approach to enhance the electrochemical performance of porous carbon materials.

Activated biochar derived from peanut shells as the electrode materials with excellent performance in Zinc-air battery and supercapacitance

The use of activated biochar-based electrode derived from waste biomass in energy technologies, such as metal-air batteries and supercapacitors, is an important strategy for realizing energy and environmental sustainability in the future. Herein, peanut shells (waste biomass) were employed to prepare activated biochar materials by pyrolysis in molten KCl and heat-treatment. The effective dispersion and corrosion effects of molten salt for the pyrolysis products during pyrolysis obviously increase defects and specific surface area of the activated biochar materials. The prepared activated biochar material (PS-800-1000) by pyrolysis in molten KCl at 800 °C and heat-treatment at 1000 °C exhibits excellent catalytic activity with half-wave potential of 0.84 V vs. RHE, comparable to commercial Pt/C for oxygen reduction reaction (ORR) in 0.1 M KOH and outstanding supercapacitance performance in 6 M KOH with high specific capacitance (355 F g^-1 at 0.5 A g^-1), which exceeds all reported biochar derived from peanut shells. The PS-800-1000-based zinc-air battery (ZAB) displays higher peak power density (141 mW cm^-2), specific capacity (767 mAh g_Zn^-1) and cycling stability than Pt/C-based ZAB. The activated biochar prepared by pyrolysis in molten KCl and heat-treatment method from peanut shells can be a promising candidate for replacing precious metals in energy conversion/storage devices.

Graphite-type activated carbon from coconut shell: a natural source for eco-friendly non-volatile storage devices

Carbon from biomass as an active material for supercapacitor electrodes has attracted much interest due to its environmental soundness, abundance, and porous nature. In this context, activated carbon prepared from coconut shells via a simple activation process (water or steam as activation agents) was used as an active material in electrodes for eco-friendly supercapacitors. X-ray diffraction (XRD), Raman spectroscopy, conductivity, scanning electron microscopy (SEM), N₂ sorption and thermogravimetry coupled to mass spectrometry (TGA-MS) studies revealed that activated carbon produced by this approach exhibit a graphitic phase, a high surface area, and large pore volume. The energy storage properties of activated carbon electrodes correlate with the morphological and structural properties of the precursor material. In particular, electrodes made of activated carbon exhibiting the largest Brunauer-Emmett-Teller (BET) surface area, i.e. 1998 m² g^-1, showed specific capacitance of 132.3 F g^-1 in aqueous electrolyte (1.5 M H₂SO₄), using expanded graphite sheets as current collector substrates. Remarkably, this sample in a configuration with ionic liquid (1-methyl-1-propy-pyrrolizinium bis(fluorosulfonyl)mide) (MPPyFSI) as electrolyte and a polyethylene separator displayed an outstanding storage capability and energy-power handling capability of 219.4 F g^-1 with a specific energy of 92.1 W h kg^-1 and power density of 2046.9 W kg^-1 at 1 A g^-1 and maintains ultra-high values at 30 A g^-1 indicating the ability for a broad potential of energy and power related applications. To the best of our knowledge, these values are the highest ever reported for ionic liquid-based supercapacitors with activated carbon obtained from the biomass of coconut shells.

More Sustainable Chemical Activation Strategies for the Production of Porous Carbons

The preparation of porous carbons attracts a great deal of attention given the importance of these materials in many emerging applications, such as hydrogen storage, CO₂ capture, and energy storage in supercapacitors and batteries. In particular, porous carbons produced by applying chemical activation methods are preferred because of the high pore development achieved. However, given the environmental risks associated with conventional activating agents such as KOH, the development of greener chemical activation methodologies is an important objective. This Review summarizes recent progress in the production of porous carbons by using more sustainable strategies based on chemical activation. The use of less-corrosive chemical agents as an alternative to KOH is thoroughly reviewed. In addition, progress achieved to date by using emerging self-activation methodologies applied to organic salts and biomass products is also discussed.

Ex-situ nitrogen-doped porous carbons as electrode materials for high performance supercapacitor

Nitrogen (N) doping of porous carbon materials is an effective strategy for enhancing the electrochemical performance of electrode materials. Herein, we report on ex-situ (post) nitrogen-doped porous carbons prepared using a biomass waste, peanut shell (PS) as a carbon source and melamine as the nitrogen source. The synthesis method involved a two-step mechanism, initial chemical activation of the PS using KOH and post N-doping of the activated carbon. The effect of the activating agent/precursor ratio and the ex-situ N-doping on the structural, textural, electrochemical properties of the porous carbons was studied. The ex-situ N-doped porous carbon with an optimum amount of KOH to PS exhibited the best capacitance performance with a specific surface area (SSA) of 1442 m² g^-1 and an enriched nitrogen content (3.2 at %). The fabricated symmetric device exhibited a 251.2 F g^-1 specific capacitance per electrode at a gravimetric current of 1 A g^-1 in aqueous electrolyte (2.5 M KNO₃) at a wide cell voltage of 2.0 V. A specific energy of 35 Wh kg^-1 with a corresponding specific power of 1 kW kg^-1 at 1 A g^-1 was delivered with the device still retaining up to 22 Wh kg^-1 and a 20 kW kg^-1 specific power even at 20 A g^-1. Moreover, long term device stability was exhibited with an 83.2% capacity retention over 20 000 charge/discharge cycles and also a good rate capability after 180 h of floating at 5 A g^-1. This great performance of the symmetric supercapacitor can be correlated to the surface porosity and post nitrogen-doping effect which increased the electrochemically-active sites resulting in a remarkable charge storage capability.

Nitridation Temperature Effect on Carbon Vanadium Oxynitrides for a Symmetric Supercapacitor

In this work, porous carbon-vanadium oxynitride (C-V₂NO) nanostructures were obtained at different nitridation temperature of 700, 800 and 900 °C using a thermal decomposition process. The X-ray diffraction (XRD) pattern of all the nanomaterials showed a C-V₂NO single-phase cubic structure. The C-V₂NO obtained at 700 °C had a low surface area (91.6 m² g⁻¹), a moderate degree of graphitization, and a broader pore size distribution. The C-V₂NO obtained at 800 °C displayed an interconnected network with higher surface area (121.6 m² g⁻¹) and a narrower pore size distribution. In contrast, at 900 °C, the C-V₂NO displayed a disintegrated network and a decrease in the surface area (113 m² g⁻¹). All the synthesized C-V₂NO yielded mesoporous oxynitride nanostructures which were evaluated in three-electrode configuration using 6 M KOH aqueous electrolyte as a function of temperature. The C-V₂NO@800 °C electrode gave the highest electrochemical performance as compared to its counterparts due to its superior properties. These results indicate that the nitridation temperature not only influences the morphology, structure and surface area of the C-V₂NO but also their electrochemical performance. Additionally, a symmetric device fabricated from the C-V₂NO@800 °C displayed specific energy and power of 38 W h kg⁻¹ and 764 W kg⁻¹, respectively, at 1 A g⁻¹ in a wide operating voltage of 1.8 V. In terms of stability, it achieved 84.7% as capacity retention up to 10,000 cycles which was confirmed through the floating/aging measurement for up to 100 h at 10 A g⁻¹. This symmetric capacitor is promising for practical applications due to the rapid and easy preparation of the carbon-vanadium oxynitride materials.