This study pioneers a transformative approach of discarded orange peels (Citrus sinensis) into highly porous carbon, demonstrating its potential application in energy storage devices. The porous carbon structure offers a substantial surface area, making it conducive for effective ion adsorption and storage, thereby enhancing capacitance. The comprehensive characterization, including X-ray diffraction, Fourier transform infrared, Raman spectroscopy, field emission scanning electron microscopy, and XPS verifies the material’s suitability for energy storage applications by confirming its nature, functional groups, graphitic structure, porous morphology and surface elemental compositions. Moreover, the introduced plasma treatment not only improves the material’s intensity, bending vibrations, and morphology but also increases capacitance, as evidenced by galvanostatic charge–discharge tests. The air plasma-treated carbon exhibits a noteworthy capacitance of 1916F/g at 0.05A/g in 2 M KOH electrolyte. long term cyclic stability has been conducted up to 10,000 cycles, the calculated capacitance retention and columbic efficiency is 92.7% and 97.6%. These advancements underscore the potential of utilizing activated carbon from agricultural waste in capacitors and supercapatteries, offering a sustainable solution for energy storage with enhanced performance characteristics.

In this study, polyimide (PI)-based activated carbon fibers (ACFs) were prepared for application as electrode materials in electric double-layer capacitors by varying the steam activation time for the PI fiber prepared under identical cross-linking conditions. The surface morphology and microcrystal structural characteristics of the prepared PI-ACFs were observed by field-emission scanning electron microscopy and X-ray diffractometry, respectively. The textural properties (specific surface area, pore volume, and pore size distribution) of the ACFs were calculated using the Brunauer–Emmett–Teller, Barrett–Joyner–Halenda, and non-local density functional theory equations based on N2/ 77 K adsorption isotherm curve measurements. From the results, the specific surface area and total pore volume of PI-ACFs were determined to be 760–1550 m2/ g and 0.36–1.03 cm3/ g, respectively. It was confirmed that the specific surface area and total pore volume tended to continuously increase with the activation time. As for the electrochemical properties of PI-ACFs, the specific capacitance increased from 9.96 to 78.64 F/g owing to the developed specific surface area as the activation time increased.

In recent times, there has been a significant demand for supercapacitors in energy storage applications due to their rapid charging– discharging capabilities, high power density, and excellent stability. Nevertheless, the synthesis of electrode materials with a substantial surface area, exceptionally high porosity, and superior electrochemical performance is still challenging. Activated carbons with a distinctive porous structure and exceptional electrochemical properties emerged as promising electrode materials for supercapacitors. In this study, we used a porous activated carbon (PAC) derived from petroleum coke followed by KOH activation as an efficient anodic electrode material. The ultra-high Brunauer–Emmett–Teller surface area of 2105.6 m2 g− 1 with stacked layers of carbon atoms arranged in a two-dimensional hexagonal structure makes the PAC an efficient candidate for a supercapacitor electrode. The PAC delivers a specific capacitance of 470 F g− 1 at a current density of 0.5 A g− 1 over a potential window of 0 to −1 V. The excellent cycling stability in a three-electrode setup with a capacitance retention of ⁓98% even at a high current density of 10 A g− 1 makes the PAC a potential anodic electrode material for high-performance supercapacitor applications.

A glassy carbon electrode modified with a composite consisting of electrodeposited chitosan and carboxylated multi-walled carbon nanotubes (e-CS/MWCNTs/GCE) was used as a working electrode for simultaneous determination of dopamine (DA), serotonin (5-HT) and melatonin (MT), which were related to circadian rhythms. The electrochemical characterizations of the working electrode were carried out via electrochemical impedance spectroscopy and chronocoulometry. It was found that electrochemical modification method, that was cyclic voltammetry, may can cause continuous CS polymerization on MWCNTs surface to form a dense membrane with more active sites on the electrode, and the electrochemically active surface area of e-CS/MWCNTs/GCE obtained was about 7 times that of GCE. The electrochemical behaviour of DA, 5-HT and MT on working electrode were carried out via differential pulse voltammetry and cyclic voltammetry. The results showed that e-CS/MWCNTs/GCE solved the problem that the bare electrode could not detect three substances simultaneously, and can catalyze oxidation potential difference as low as 0.17 V of two substances reaction at the same time, indicating very good electrocatalytic activity. By optimizing the detection conditions, the sensor showed a good linear response to DA, 5-HT and MT in the range of 20-1000 μmol/L, 9-1000 μmol/L and 20-1000 μmol/L, and the detection limits were 12 μmol/L, 10 μmol/L and 22 μmol/L (S/N = 3), respectively. In addition, the proposed sensor was successfully applied to the simultaneous detection of DA, 5-HT and MT in human saliva samples.

In the present study, an innovative electrochemical sensing platform was established for sensitive detection of NO2 —. This sensor was developed using CoFe alloy encapsulated in nitrogen-doped carbon nanocubes (named as CoFe@NC-NCS), synthesized through the calcination of polydopamine-coated CoFe Prussian-blue analogues (CoFe-PBA@PDA). The morphological and electrochemical characterization reveals that the CoFe@NC-NCS possesses high electrocatalytic activity for electrochemical quantitation of NO2 —, ascribed to the huge surface area and plentiful active positions, benefiting from the porous, hollow, and core–shell structure of CoFe@NC-NCS. Under the optimal conditions, CoFe@NC-NCS/GCE possessed remarkable sensing performance for NO2 — with wide liner ranges and a detection limit of 0.015 μM. NO2 — recovery experiments in real samples exhibited recoveries in the range of 98.8–103.5%. Hence, the CoFe@NC-NCS shows great promise for the construction of electrochemical sensor with more potential application.

Energy storage for sustainable development and progress of power production industries is vitally important. The energy storage devices are under extensive research from last three decades to ensure the hand-on-hand coordination with power supply phenomenon and to reduce the energy loses in lines. The cost-effective materials are still highly demanding as an electrode material for energy storage devices. Biomass-derived carbon materials are best candidates due to their low cost, relatively high abundance, pollution-free nature. Here, we are reporting a facile two-step green approach to convert Himalayan horse chestnuts (HHCNs) into activated carbon materials. In first step, grinding and pyrolysis of the HHCNs were carried out, and then activation was performed using KOH to enhance the pore density and surface area. HHCNs-derived carbon was utilized as an electrode in electrical double-layer capacitors (EDLCs) with 1 M H2SO4 as an electrolyte. The macroporous structure along with hierarchical porous network acts as an efficient source of transportation of charges across the electrode and separator. Cyclic voltammetry test was taken from 10 to 100 mV/s current and within a range of 0–1 V applied potential; approximately rectangular CV shown mirror response towards current and shown typical EDLCs properties. The proximate analysis confirms the presence of heteroatoms like sulfur, oxygen, and nitrogen which act as carbon dopants. The wettability of HHCNs-derived carbon enhanced due to the various types of oxygen functionalities inherited from the lignin skeletal part. The nitrogen content is primarily responsible for the pseudo-capacitive behavior of HHCNs-codoped carbon. HHCNs-derived activated carbon materials has emerged as a promising electrode material for energy storage applications.

Small-film-type ion sensors are garnering considerable interest in the fields of wearable healthcare and home-based monitoring systems. The performance of these sensors primarily relies on electrode capacitance, often employing nanocomposite materials composed of nano- and sub-micrometer particles. Traditional techniques for enhancing capacitance involve the creation of nanoparticles on film electrodes, which require cost-intensive and complex chemical synthesis processes, followed by additional coating optimization. In this study, we introduce a simple one-step electrochemical method for fabricating gold nanoparticles on a carbon nanotube (Au NP–CNT) electrode surface through cyclic voltammetry deposition. Furthermore, we assess the improvement in capacitance by distinguishing between the electrical double-layer capacitance and diffusion-controlled capacitance, thereby clarifying the principles underpinning the material design. The Au NP–CNT electrode maintains its stability and sensitivity for up to 50 d, signifying its potential for advanced ion sensing. Additionally, integration with a mobile wireless data system highlights the versatility of the sensor for health applications.

Graphitic carbon nitride (g-C3N4) has attracted extensive attention in energy storage due to its suitable and tunable bandgap, high chemical/thermal stability, earth abundance and environmental friendliness. However, its conductivity should be improved to work as the electrode materials in supercapacitors. In this report, we have prepared a two-dimensional composite (CN-PANI) based on g-C3N4 and polyaniline (PANI) by in-situ polymerization, which can be efficiently applied as electrode material for supercapacitors. The introduction of PANI can increase the conductivity of the electrode, and the porous structure of g-C3N4 can provide enough channels for the transport of electrolyte ions and improve the electrode stability. As a result, the obtained CN-PANI demonstrates excellent specific capacitance (234.0 F g− 1 at 5 mV/s), good rate performance and high cycling stability (86.2% after 10,000 cycles at 50 mV/s), showing great potential for high-rate supercapacitors.

In this work, a nanocomposite containing gold (Au) nanofibers decorated iron-metal–organic framework (Fe-MOF) was successfully synthesized for electrochemical detection of acetaminophen (AAP). The as-synthesized Au@Fe-MOF nanocomposite was confirmed by various characterization techniques. Morphological analysis showed that the Au nanofibers with an average size of less than 10 nm were dispersed on the Fe-MOF. Cyclic voltammetric analysis showed that the Au@Fe-MOF nanocomposite showed well-defined redox peaks with higher current than that of GCE and Fe-MOF. The Au@Fe-MOF/ GCE exhibited a linear range, sensitivity, and detection limit of 0.5–18 μM, 4.95 μM/μA/cm2, and 0.12 μM, respectively. The Au@Fe-MOF/GCE showed a very low response for the interference materials. The real sample analysis revealed that the Au@Fe-MOF/GCE showed good recovery towards the AAP in urine and paracetamol. Therefore, the developed sensor can be used for quality control of AAP.

The central theme of this work is the synthesis of single-walled carbon nanotubes (SWCNTs) through the chemical vapor deposition method (CVD). Single-walled carbon nanotubes are synthesized using catalyst-chemical vapor deposition of acetylene at 750 °C temperature. X-ray diffraction study gives a characteristic peak (002) at 26.55° corresponding to the existence of carbon nanotube confirms that the particles are crystalline in nature and hexagonal phase. An SEM and HRTEM outcome gives surface morphology of SWCNTs. The elemental composition was confirmed by EDAX. The ideal concentration of single-walled carbon nanotubes was used to design a novel electrochemical sensor for determining paracetamol (PA) using cyclic voltammetry. Electrochemical determination of paracetamol is described using a single-walled carbon nanotube modified carbon paste electrode (SWCNT/MCPE). The SWCNT/MCPE was used in this study to detect paracetamol electrochemically at pH 7.2 in a 0.2 M PBS with a scan rate of 50 mV s− 1. A single-walled nanotube modified carbon paste electrode was used to develop a sensitive and selective electrochemical technique for the detection of PA. The SWCNT/MCPE showed excellent electrocatalytic activity towards the oxidation of paracetamol in phosphate buffer solution. Therefore, with increased oxidation currents, the voltammetric responses of paracetamol at the bare carbon paste electrode are organized within cyclic voltammetric peaks.

This study compares the characteristics of a compact TiO2 (c-TiO2) powdery film, which is used as the electron transport layer (ETL) of perovskite solar cells, based on the manufacturing method. Additionally, its efficiency is measured by applying it to a carbon electrode solar cell. Spin-coating and spray methods are compared, and spraybased c-TiO2 exhibits superior optical properties. Furthermore, surface analysis by scanning electron microscopy (SEM) and atomic force microscopy (AFM) exhibits the excellent surface properties of spray-based TiO2. The photoelectric conversion efficiency (PCE) is 14.31% when applied to planar perovskite solar cells based on metal electrodes. Finally, carbon nanotube (CNT) film electrode-based solar cells exhibits a 76% PCE compared with that of metal electrodebased solar cells, providing the possibility of commercialization.

Nitrophenol sensors have garnered interest in pharmaceuticals, agriculture, environment safety and explosives. Various methods have been proposed to detect 4-nitrophenol, but nitrophenol isomers such as 2,4-dinitrophenol (DNP) and 2,4,6-trinitrophenol have been comparatively less studied. For the first time, the present work explores graphitic nanocarbon, i.e., carbon black (CB) interface for sensing of DNP. Two reduction potentials were noted at − 0.48 and − 0.64 V for o-NO2 and p-NO2 moieties, respectively, at CB/GCE. At the same time, bare GCE (glassy carbon electrode) shows a single reduction potential at − 0.7 V. The electrocatalytic effect and adsorption ability of the interface was studied from the DNP concentration effect. Scan rate and pH studies suggest that the CB acquires four electrons for NO2 reduction by the diffusion phenomenon. A broad detection range of 10–250 μM DNP with a very low detection limit of 0.13 (o-form) and 0.15 μM (p-form) was achieved using the CB interface. The real-time applicability of the fabricated sensor was evaluated using commercially available beverages with excellent recovery values. The stability, repeatability and reproducibility of the CB interface were successfully confirmed. Comparison of the sensing parameters of the developed sensor with those reported in literature reveals excellent detection limit and response time for the CB-interfaced DNP sensor, indicating its potential for environmental and commercial applications.

Herein, a new and generic strategy has been proposed to introduce uniformly distributed graphitic carbon into the nanostructured metal oxide. A facile and generic synthetic protocol has been proposed to introduce uniformly distributed conducting graphitic carbon into the Co3O4 nanoparticles ( Co3O4 NPs@graphitic carbon). The prepared Co3O4 NPs@graphitic carbon has been drop casted onto the portable screen-printed electrode (SPE) to realize its potential application in the individual and simultaneous quantification of toxic Pb(II) and Cd(II) ions present in aqueous solution. The proposed Co3O4 NPs@graphitic carbon-based electrochemical sensor exhibits a wide linear range from 0 to 120 ppb with limit of detection of 3.2 and 3.5 ppb towards the simultaneous detection of Pb(II) and Cd(II), which falls well below threshold limit prescribed by WHO.

Activated non-graphitizable hard carbon using orange peel with mesoporous structure has been prepared by pyrolyzation at 700, 800, 900 °C using chemical activation method. The activated orange peel-derived hard carbon has been characterized for its mesoporous and disordered structure. TG-DSC gives the information for the changes about sample composition and thermal stability of the materials. Increasing the carbonization temperature for orange peel precursor using NaOH as activating agent, elevates the pore diameter, which thereby facilitating the insertion of Na+. Raman and X-ray diffraction confirms the presence of disordered carbon. The surface morphology of the material was analyzed by scanning eletron microsope and nitrogen ( N2) adsorption and desorption analysis give the morphology, mesopore size (3.374, 3.39 and 4 nm) and surace area (60.164, 58.99 and 54.327 m2/g) of the orange peel-derived hard carbon. Hence, this work strongly evidences that the biomass-derived hard carbon with good porosity and paves way of superior electrochemical performance for emerging sodium ion batteries.

Doped porous carbon materials have attracted great interest owing to their excellent electrochemical performance toward energy storage applications. In this report, we described the synthesis of nitrogen-doped porous carbon (N-PC) via carbonization of a triazine-based covalent organic framework (COF) synthesized by Friedel–Crafts reaction. The as-synthesized COF and N-PC were confirmed by X-ray diffraction. The N-PC exhibited many merits including high surface area (711 m2 g−1), porosity, uniform pore size, and surface wettability due to the heteroatom-containing lone pair of electron. The N-PC showed a high specific capacitance of 112 F g−1 at a current density of 1.0 A g−1 and excellent cyclic stability with 10.6% capacitance loss after 5000 cycles at a current density of 2.0 A g−1. These results revealed that the COF materials are desirable for future research on energy storage devices.

The carbon spheres (CSs) synthesized by an ultrasonic-spray pyrolysis method were activated for supercapacitor electrode. There are plenty of cracks on the surface of the activated carbon spheres (ACSs), which expend with increasing the activation temperature and activator dosage. The specific capacitance of ACSs increases with the activation temperature and activator dosage and reach to maximal value at certain conditions. Importantly, the ACS sample activated at relatively low activation temperature (600 °C) and 7 of mass ratio of KOH to CSs has the highest specific capacitance (about 209 F g− 1 at 50 mA g− 1 of current density) and indicates the excellent cycling stability after 1000 consecutive charge–discharge cycles. Furthermore, the graphene sheets could be found in the samples that were activated at 1000 °C. And the electrode prepared by the sample has the very low series resistance because of the excellent conductivity of the formed graphene sheets.

A carbon nanofiber was produced from the Areca catechu husk as a supercapacitor electrode, utilizing a chemical activation of potassium hydroxide (KOH) at different concentrations. One-stage integrated pyrolysis both carbonization and physical activation were employed for directly converting biomass to activated carbon nanofiber. The morphology structure, specific surface area, pore structure characteristic, crystallinity, and surface compound were characterized to evaluate the influence on electrochemical performance. The electrochemical performance of the supercapacitor was measured using cyclic voltammetry (CV) through a symmetrical system in 1 M H2SO4. The results show that the KOH-assisted or absence activation converts activated carbon from aggregate into a unique structure of nanofiber. The optimized carbon nanofiber showed the large specific surface area of 838.64 m2 g−1 with the total pore volume of 0.448 cm3 g−1, for enhancing electrochemical performance. Beneficial form its unique structural advantages, the optimized carbon nanofiber exhibits high electrochemical performance, including a specific capacitance of 181.96 F g−1 and maximum energy density of 25.27 Wh kg−1 for the power density of 91.07 W kg−1. This study examines a facile conventional route for producing carbon nanofiber from biomass Areca catechu husk in economical and efficient for electrode supercapacitor.

Vertically Aligned Carbon Nanotubes (VACNTs)-coated flexible aluminium (Al) foil is studied as an electrode for supercapacitor applications. VACNTs are grown on Al foil inside thermal Chemical Vapor Deposition (CVD) reactor. 20 nm thick layer of Fe is used as a catalyst while Ar, H2 and C2H2 are used as precursor gases. The effect of growth temperature on the structure of CNTs is studied by varying the temperature of CVD reactor from 550 °C to 625 °C. Better alignment of VACNTs arrays on Al foil is recorded at 600 °C growth temperature in comparison to other processing temperatures. Cyclic voltammetry results shows that VACNTs-coated Al foil has a specific capacitance of ~ 3.01 F/g at a scan rate of 50 mV/s. The direct growth of VACNT array results in better contact with Al foil and thus low ESR values observed in impedance spectroscopy analysis. This leads to a fast charge–discharge cycle as well as a very high value of power density (187.79 kW/ kg) suitable for high power applications. Moreover, wettability study shows that the fabricated VACNT electrode has a contact angle of more than 152° which signifies that it is a superhydrophobic surface and hence shows lower specific capacitance in comparison to reported values for VACNT array. Therefore, it is necessary to develop suitable post-processing strategies to make VACNTs hydrophilic to realize their full potential in supercapacitor applications.

Engineering the microstructure of the carbonaceous materials is a promising strategy to enhance the capacitive performance of supercapacitors. In this work, nanostructured Black Pearl (1500 BP) carbon which is a conductive carbon being commercially used in printing rolls, conductive packaging, conductive paints, etc. is analyzed for its feasibility as an electrode material for Electric Double-Layer Capacitors (EDLCs). To achieve that commercial Black Pearl (BP), carbon is treated with mild acid H3PO4 to remove the impurities and enhance the active sites by regulating the growth of agglomerates and creating micropores in the nano-pigments. Generally, the coalescence of nanoparticles owing to their intrinsic surface energy has tendency to create voids of different sizes that act like meso/micropores facilitating the diffusion of ions. The electrochemical performance of BP carbon before and after chemical activation is investigated in aqueous ( H2SO4, KOH and KCl) and a non-aqueous electrolyte (1 M TEMABF4 in acetonitrile) environment employing different electrochemical techniques such as Cyclic Voltammetry (CV), Galvanostatic charge/discharge (GCD) and Electrochemical Impendence Spectroscopy (EIS). The chemically activated BP carbon delivers the highest specific capacitance of ∼156 F g−1 in an aqueous electrolyte, 6 M KOH. The highest specific power, ~ 15.3 kW kg−1 and specific energy, 14.6 Wh kg−1 are obtained with a symmetric capacitor employing non-aqueous electrolyte because of its high working potential, 2.5 V.