Showing papers on "Cyclic voltammetry published in 2022"

A polypyrrole/GO/ZnO nanocomposite modified pencil graphite electrode for the determination of andrographolide in aqueous samples

Abstract: This paper presents a novel electrochemical sensor based on a pencil graphite electrode (PGE) modified with molecularly imprinted graphene oxide/zinc oxide nanocomposites for a sensitive detection of andrographolide. This is the first report of the novel method of electroanalytical determination of andrographolide through a modified PGE. The modified PGE was successfully fabricated and characterized. Then, quantitative analyses were performed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The optimum conditions for this analysis were the supporting electrolyte containing 0.1 M KCl and 0.001 M K3Fe(CN)6, citrate buffer of pH 4, modulation amplitude of 50 mV, and scan rate of 10 mV/s. Under optimized parameters, a good linear response was obtained for andrographolide detection by DPV with a range of 50–145 µM and a detection limit of 42.6 µM. The relative standard deviation (R.S.D.) of the three measurements is 1.47%, which shows the excellent repeatability of the proposed method, while reproducibility analysis produced a R.S.D. value of 4.46%. The proposed technique with optimum conditions exhibited good selectivity towards the detection of andrographolide in the presence of ascorbic acid, uric acid, and cyclodextrin. This method was successfully applied to determine andrographolide in real water samples, and the results are comparable with the established method.

Polypyrrole Based Molecularly Imprinted Polymer Platform for Klebsiella pneumoniae Detection

Abstract: The present work describes the synthesis of molecular imprinting polymer (MIP) and electrochemical sensing of Klebsiella pneumonia (K. pneumonia) bacteria by electrochemical technique. K. pneumonia has far reached ill effects on the human body, hence it is essential to monitor its levels. A MIP platform based on polypyrrole (PPy) was developed for electrochemical sensing of K. pneumonia to monitor its levels. The developed sensor has good sensitivity (3 μA ml CFU-cm−2), a low limit of detection (LOD) of 1.352 CFU ml−1 in the linear detection range of 1 to 105 CFU per ml. The molecular imprinting was carried out by polymerization of pyrrole in the presence of K. pneumonia and then removed the bacteria by ultrasonication to obtain the MIP. The fabrication of electrodes is done by electrophoretic deposition (EPD) of MIP onto the hydrolyzed ITO-coated glass surface. The detection was done by the electrochemical differential pulse voltammetry (DPV) technique. The synthesized final product is then characterized by Fourier transform infrared spectroscopy (FTIR) technique to understand its structure and confirm the successful synthesis of the desired MIP. The selectivity studies were performed against two other bacteria and different ions that are present in healthy human urine. To check the applicability in real sample studies, spiked urine samples were used.

Intermolecular Energy Gap‐Induced Formation of High‐Valent Cobalt Species in CoOOH Surface Layer on Cobalt Sulfides for Efficient Water Oxidation

Abstract: Transition metal-based electrocatalysts will undergo surface reconstruction to form active oxyhydroxide-based hybrids, which are regarded as the “true-catalysts” for the oxygen evolution reaction (OER). Much effort has been devoted to understanding the surface reconstruction, but little on identifying the origin of the enhanced performance derived from the substrate effect. Herein, we report the electrochemical synthesis of amorphous CoOOH layers on the surface of various cobalt sulfides (CoSα), and identify that the reduced intermolecular energy gap (Δinter) between the valence band maximum (VBM) of CoOOH and the conduction band minimum (CBM) of CoSα can accelerate the formation of OER-active high-valent Co4+ species. The combination of electrochemical and in situ spectroscopic approaches, including cyclic voltammetry (CV), operando electron paramagnetic resonance (EPR) and Raman, reveals that Co species in the CoOOH/Co9S8 are more readily oxidized to CoO2/Co9S8 than in CoOOH and other CoOOH/CoSα. This work provides a new design principle for transition metal-based OER electrocatalysts.

An electrochemical sensor for detection of trace-level endocrine disruptor bisphenol A using Mo2Ti2AlC3 MAX phase/MWCNT composite modified electrode.

Abstract: Bisphenol A (BPA) is an industrially preferred material for the production of plastic and polycarbonate as well as a used material for the interior of food and beverage cans. In this study, synthesis and electrochemical sensor application of Mo2Ti2AlC3/MWCNT (multi-walled carbon nanotube) nanocomposite for BPA sensing was evaluated. Mo2Ti2AlC3 was used as MAX phase material in the design of the sensor, and MWCNT was preferred to increase conductivity and sensitivity. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to determine Mo2Ti2AlC3/MWCNT nanocomposite's electrochemical sensor performances which had LOD of 2.7 nM and LOQ of 8.91 nM in the linear working range of 0.01-8.50 μM calculated from DPV. The composite showed a single oxidation step against BPA which is diffusion-controlled and irreversible. The sensor was successfully applied for the determination of BPA in milk pack, plastic bottle, and can with recoveries ranging from 95.67% to 100.60%. In addition, sensor performance was examined through selectivity, repeatability, and reusability studies. HPLC as a standard determination method was carried out for accuracy of the voltammetric determination method in the real samples. The developed sensor could be applied to different areas from industry quality control to clinical analysis for the detection of BPA.

Electrochemical deposition of uniform and porous Co–Ni layered double hydroxide nanosheets on nickel foam for supercapacitor electrode with improved electrochemical efficiency

Abstract: In this study, Co–Ni layered double hydroxide (LDH) nanosheets are synthesized on nickel foam (NF) using a simple, facile, and cost effective electrochemical deposition method. We present a comparative study of Co–Ni LDH nanosheets on NF for use in supercapacitor electrodes. The method is based on electrochemical deposition using cyclic voltammetry (CV) with different cycles (4, 6, 8, and 10 cycles). Compared to other cycles, the Co–Ni LDH nanosheets on NF as electrode materials obtained higher specific capacitance at eight cycles. In 1 M potassium hydroxide (KOH), a significant specific capacitance of 3130.8 F/g was obtained at a scan rate of 5 mV/s, with good cyclic stability of 72.4% capacitance retention after 3000 cycles. The uniform and porous structure of Co–Ni LDH nanosheets on NF and the fast ion transfer between the electrolyte–electrode interface and reduced resistance contribute to this superior electrochemical efficiency, confirmed by CV and electrochemical impedance (EIS) studies. Co–Ni LDH nanosheets on NF are promising candidates for low-cost high-efficiency energy storage electrode materials for supercapacitor applications because of their superior performance and ease of preparation.

Structural and electrochemical performance of carbon coated molybdenum selenide nanocomposite for supercapacitor applications

Abstract: Among the recent trends of supercapacitor electrode materials, transition metal dichalcogenides based composite materials have become popular due to their ability to have high electronic conductivity, variable oxidation states, large surface area, a porous structure. Herein we report, a composite material based on MoSe 2 as electrode prepared using a standard single-step hydrothermal strategy. The structural and morphological study of the prepared material confirms the formation of the composite. The specific surface area has been estimated using BET technique and found to 522 m 2 g − 1 with average pore diameter as 4.6 nm. In all prepared composite electrodes, M@AC 1:5 electrode exhibits the highest specific capacity of 514 F g − 1 at a scan rate of 10 mV s − 1 for potential window 1 V in KOH electrolyte solution. The electrochemical impedance spectroscopy (EIS) study of the M@AC 1:5 electrode shows good agreement with cyclic voltammetry and galvanostatic charge-discharge storage mechanism. The aqueous symmetric cell fabricated of M@AC 1:5 with 6 M KOH electrolyte exhibits energy and power density 39.4 Wh kg −1 and 704.5 W kg −1 respectively. It shows long cycle stability with 90% capacitance retention and 100% coulombic efficiency even after 10,000 cycles. Further, the symmetric cell of M@AC 1:5 material was applied for lighting red LED, which illuminated for 22 min. The charging /discharging mechanism has been proposed based on finding of results through different characterizations. The asymmetric supercapacitor has also been designed using two different electrodes (first M@AC 1:5 and second synthetic MWCNT) and shows energy density of 14.9 Wh kg −1 and power density of 496 W kg −1 respectively. The capacitance retention is maintained up to 86.6% while coulombic efficiency recorded 100% for 10,000 cycles. Thus, obtained results highly encouraging and appropriate for the commercial applications.

Quasihexagonal Platinum Nanodendrites Decorated over CoS2‐N‐Doped Reduced Graphene Oxide for Electro‐Oxidation of C1‐, C2‐, and C3‐Type Alcohols

Abstract: The development of efficient and highly durable materials for renewable energy conversion devices is crucial to the future of clean energy demand. Herein, cage‐like quasihexagonal structured platinum nanodendrites decorated over the transition metal chalcogenide core (CoS2)‐N‐doped graphene oxide (PtNDs@CoS2‐NrGO) through optimized shape engineering and structural control technology are fabricated. The prepared electrocatalyst of PtNDs@CoS2‐NrGO is effectively used as anodic catalyst for alcohol oxidation in direct liquid alcohol fuel cells. Notably, the prepared PtNDs@CoS2‐NrGO exhibits superior electrocatalytic performance toward alcohol oxidation with higher oxidation peak current densities of 491.31, 440.25, and 438.12 mA mgpt–1 for (methanol) C1, (ethylene glycol) C2, and (glycerol) C3 fuel electrolytes, respectively, as compared to state‐of‐the‐art Pt‐C in acidic medium. The electro‐oxidation durability of PtNDs@CoS2‐NrGO is investigated through cyclic voltammetry and chronoamperometry tests, which demonstrate excellent stability of the electrocatalyst toward various alcohols. Furthermore, the surface and adsorption energies of PtNDs and CoS2 are calculated using density functional theory along with the detailed bonding analysis. Overall, the obtained results emphasize the advances in effective precious material utilization and fabricating techniques of active electrocatalysts for direct alcohol oxidation fuel cell applications.

Vertical silica nanochannels supported by nanocarbon composite for simultaneous detection of serotonin and melatonin in biological fluids

Abstract: Herein we report the simultaneous determination of serotonin (5-HT) and melatonin (MT) by using highly ordered and vertically-oriented mesoporous silica-nanochannel films (VMSF) on highly electrochemically reduced graphene oxide-carbon nanotubes (HErGO-CNT) composite substrate. Such VMSF/HErGO-CNT with compact 2D–2D layered structure is fabricated on indium tin oxide (ITO) electrodes via a two-step electrochemical process, namely the electrodeposition of ErGO-CNT film onto the ITO surface by cyclic voltammetry and subsequently growth of VMSF on the ErGO-CNT/ITO surface by electrochemically assisted self-assembly method, during which graphene oxide (GO) is subjected to the two-time electrochemical reduction to form HErGO. The CNT encased in the GO sheets served as electronic conducting wires, which not only can promote the electrochemical reduction of GO but also contribute to a certain degree of hydrophobicity, facilitating the controllable electrodeposition of ErGO-CNT composites on ITO under its safe use potential window. In addition, doping CNT is able to enlarge the layer gap between graphene sheets and thus improves the electroactive area and mass transfer of the nanocarbon composite substrate. Furthermore, the underlying HErGO-CNT acts as an efficient electroactive layer and the outer VMSF possesses electrostatic preconcentration and anti-fouling functions, synergistically realizing the direct electrochemical analysis of 5-HT and MT in two complex biological fluids (human whole blood and artificial cerebrospinal fluid).

One-step electrodeposition of a polypyrrole/NiO nanocomposite as a supercapacitor electrode

Abstract: An electrochemical deposition technique was used to fabricate polypyrrole (Ppy)/NiO nanocomposite electrodes for supercapacitors. The nanocomposite electrodes were characterized and investigated by Fourier transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The performance of supercapacitor electrodes of Ppy/NiO nanocomposite was enhanced compared with pristine Ppy electrode. It was found that the Ppy/NiO electrode electrodeposited at 4 A/cm-2 demonstrated the highest specific capacitance of 679 Fg-1 at 1 Ag-1 with an energy density of 94.4 Wh kg-1 and power density of 500.74 W kg-1. Capacitance retention of 83.9% of its initial capacitance after 1000 cycles at 1 Ag-1 was obtained. The high electrochemical performance of Ppy/NiO was due to the synergistic effect of NiO and Ppy, where a rich pores network-like structure made the electrolyte ions more easily accessible for Faradic reactions. This work provided a simple approach for preparing organic-inorganic composite materials as high-performance electrode materials for electrochemical supercapacitors.