1,721,066 research outputs found
Electroanalysis of ascorbate and dopamine at a gold electrode modified with a positively charged self-assembled monolayer
No full textThe self-assembled monolayer (SAM) of a di-positive nickel macrocycle (1) (dinickel(II) (2,2′-bis(1,3,5,8,12-pentaazacyclotetradec-3-yl)-diethyl disulfide) perchlorate) has been utilized for the electroanalysis of ascorbate (AA) and dopamine (DA). A very large decrease (∼450 mV) in the overpotential for the oxidation of AA has been observed at the SAM-1 modified gold electrode. The electrostatic interaction of negatively charged AA with the di-positive SAM-1 facilitates the oxidation of AA at the monolayer-modified electrode. The electrostatic interaction of AA with the SAM-1 has been verified with the mixed monolayers of 1 and diethyl disulfide (DEDS). The peak potential for the oxidation of AA shifts towards more positive potential and the oxidation peak current decreases as the fraction of DEDS increases. The oxidation of DA at the monolayer-modified electrode is less favorable owing to the electrostatic repulsion between DA and the di-positive monolayer. The SAM-1 modified gold electrode resolves well the voltammetric peaks of these analytes, which are indistinguishable at the bare electrode. The catalytic oxidation of AA by oxidized DA has been successfully eliminated at the monolayer-modified electrode. The SAM-1 electrode has been used for the simultaneous determination of AA and DA. The results obtained at the SAM-1 electrode are compared with those at the gold electrode modified with a mono-positive monolayer of cystamine (CYST)
Electrochemically triggered michael addition on the self-assembly of 4-thiouracil: Generation of surface-confined redox mediator and electrocatalysis
No full textGeneration of a surface-confined redox mediator (RM) by an electrochemically triggered Michael addition reaction and the electrocatalytic properties of the mediator are described. Electrogenerated o-quinone undergoes Michael addition reaction with the self-assembled monolayer (SAM) of 4-thiouracil (4-TU) on a gold (Au) electrode and yields a surface-confined RM, 1-(3,4-dihydroxyphenyl)-4-mercapto-1H-pyrimidin-2-one (DPTU). The Michael addition reaction depends on the electrolysis potential and time, solution pH, and concentration of catechol (CA) used in the reaction. The redox mediator, DPTU, exhibits reversible redox response, characterstic of a surface-confined species at ∼0.22 V in neutral pH. The anodic peak potential of DPTU shifts by 58 ± 2 mV while changing the solution pH by one unit, suggesting that protons and electrons taking part in the redox reaction are in the ratio of 1:1. The apparent rate constant (kapps) for the heterogeneous electron-transfer reaction of the RM was determined to be 114 ± 5 s-1. The surface coverage (Γ) of DPTU on the electrode surface was 8.2 ± 0.1 × 10-12 mol/cm2. DPTU shows excellent electrocatalytic activity toward oxidation of reduced nicotinamide adenine dinucleotide (NADH) with activation overpotential, which is ∼600 mV lower than that observed at the unmodified Au electrode. The dipositive cations in the supporting electrolyte solution amplify the electrocatalytic activity of DPTU. A 2.5-fold enhancement in the catalytic current was observed in the presence of Ca2+ or Ba2+ ions. The sensitivity of the electrode toward NADH in the presence and absence of Ca2+ ions was 0.094 ± 0.011 and 0.04 ± 0.0071 nA cm-2 nM-1, respectively. A linear increase in the catalytic current was obtained up to the concentration of 0.8 mM, and the electrode can detect amperometrically as low as 25 nM of NADH in neutral pH
Nitrogen electrocatalysis: Electrolyte engineering strategies to boost faradaic efficiency
No full textThe electrochemical activation of dinitrogen at ambient temperature and pressure for the synthesis of ammonia has drawn increasing attention. The faradaic efficiency (FE) as well as ammonia yield in the electrochemical synthesis is far from reaching the requirement of industrial-scale production. In aqueous electrolytes, the competing electron-consuming hydrogen evolution reaction (HER) and poor solubility of nitrogen are the two major bottlenecks. As the electrochemical reduction of nitrogen involves proton-coupled electron transfer reaction, rationally engineered electrolytes are required to boost FE and ammonia yield. In this Review, we comprehensively summarize various electrolyte engineering strategies to boost the FE in aqueous and non-aqueous medium and suggest possible approaches to further improve the performance. In aqueous medium, the performance can be improved by altering the electrolyte pH, transport velocity of protons, and water activity. Other strategies involve the use of hybrid and water-in-salt electrolytes, ionic liquids, and non-aqueous electrolytes. Existing aqueous electrolytes are not ideal for industrial-scale production. Suppression of HER and enhanced nitrogen solubility have been observed with hybrid and non-aqueous electrolytes. The engineered electrolytes are very promising though the electrochemical activation has several challenges. The outcome of lithium-mediated nitrogen reduction reaction with engineered non-aqueous electrolyte is highly encouraging
Electrocatalytic sensing of NADH at an in situ functionalized self-assembled monolayer on gold electrode
No full textIn situ functionalization of a self-assembled monolayer (SAM) of an aromatic thiol, 4-aminothiophenol (4-ATP), on gold electrode in neutral pH yields a redox active monolayer of 4′-mercapto-N-phenylquinone diimine (NPQD). The in situ functionalized electrode shows an excellent electrocatalytic activity towards the oxidation of NADH with an activation overpotential, which is ca. 600 mV lower than that at the bare electrode. The sensitivity of the functionalized electrode towards the oxidation of NADH was found to be 0.0030±0.0003μA/μM. The electrode shows a linear response for a wide range of concentration (10–190 μM) and it can detect as low as 10 μM NADH at neutral pH. The mixed monolayer of cystamine (CYST) and NPQD is used to mitigate the interference of ascorbate (AA) in the measurement of NADH. The selective electrocatalytic sensing of NADH in the presence of AA at the mixed monolayer modified electrode is demonstrated for the first time
Amperometric biosensing of glutamate using carbon nanotube based electrode
No full textAmperometric biosensing of glutamate using nanobiocomposite derived from multiwall carbon nanotube (CNT), biopolymer chitosan (CHIT), redox mediator meldola’s blue (MDB) and glutamate dehydrogenase (GlDH) is described. The CNT composite electrode shows a reversible voltammetric response for the redox reaction of MDB at −0.15 V; the composite electrode efficiently mediates the oxidation of NADH at −0.07 V, which is 630 mV less positive than that on an unmodified glassy carbon (GC) electrode. The CNTs in the composite electrode facilitates the mediated electron transfer for the oxidation of NADH. The CNT composite electrode is highly sensitive (5.9 ± 1.52 nA/μM) towards NADH and it could detect as low as 0.5 μM of NADH in neutral pH. The CNT composite electrode is highly stable and does not undergo deactivation by the oxidation products. The electrode does not suffer from the interference due to other anionic electroactive compounds such as ascorbate (AA) and urate (UA). Separate voltammetric peaks have been observed for NADH, AA and UA, allowing the individual or simultaneous determination of these bioanalytes. The glutamate biosensor was developed by combining the electrocatalytic activity of the composite film and GlDH. The enzymatically generated NADH was electrocatalytically detected using the biocomposite electrode. Glutamate has been successfully detected at −0.1 V without any interference. The biosensor is highly sensitive, stable and shows linear response. The sensitivity and the limit of detection of the biosensor was 0.71 ± 0.08 nA/μM and 2 μM, respectively
Facile in situ synthesis of multiwall carbon nanotube supported flowerlike Pt nanostructures: an efficient electrocatalyst for fuel cell application
No full textMultiwall carbon nanotube (MWCNT)-supported flowerlike Pt nanostructure with pronounced electrocatalytic activity in the reduction of oxygen and oxidation of methanol was synthesized by wet chemical hydrogen reduction route. The Pt nanostructures on the MWCNT were characterized by transmission electron microscopic, field emission scanning electron microscopic, X-ray diffraction (XRD), X-ray photoelectron spectroscopic, and electrochemical measurements. The Pt nanostructures on MWCNT have flowerlike morphology with an average size of 80 nm. XRD and selective area electron diffraction measurements show that the Pt nanoflowers are crystalline and have face centered cubic structure. The flowerlike Pt nanostructure shows excellent electrocatalytic activity toward oxygen reduction and methanol oxidation reactions. The electrocatalytic performance of the nanoelectrocatalyst was evaluated in terms of catalytic current density, stability, and reduction/oxidation potential. The particle loading strongly controls the electrocatalytic activity. High-catalytic current density was obtained at lower loading of the nanoelectrocatalyst. The kinetics of oxygen reduction reaction was analyzed using rotating ring-disk electrode system. The nanoelectrocatalyst favors the 4-electron pathway for the reduction of oxygen at favorable potential. The electrochemical impedance spectroscopic (EIS) measurement was used to evaluate the performance of the catalyst toward methanol oxidation. The EIS response of the electrode toward oxidation of methanol strongly depends on the electrode potential. Capacitive, inductive, and pseudoinductive behaviors, depending on the electrode potential, were observed. The charge transfer resistance decreases gradually while increasing the potential from 0.5 to 0.8 V. Negative impedance was obtained at the potential of 1.0 V. The electrocatalytic performance of flowerlike nanostructure is significantly higher than the conventional spherical nanoparticles. The shape and surface morphology of the nanoparticles have profound effect in their electrocatalytic activity
Facile shape-controlled growth of hierarchical mesoporous δ-MnO<sub>2</sub>for the development of asymmetric supercapacitors
No full textSynthesis of pseudocapacitive mesoporous transition metal oxides with hierarchical structures is of great interest in the development of high performance energy storage devices. Herein, we demonstrate a facile single-step, template-free chemical route for the synthesis of hierarchical mesoporous δ-MnO2 and its supercapacitive performance. The mesoporous δ-MnO2 is synthesized by the thermodynamically favourable redox reaction of MnO4− with HBr. The growth of δ-MnO2 involves the facile reduction of MnO4-. to Mn2+. and the subsequent reaction of in situ generated Mn2+. with unreacted Mn4- in one pot at room temperature. Br- has dual roles of reducing MnO4- and controlling the growth of MnO2 by surface etching. The possible Ostwald ripening and self-assembling of the nanoseeds formed at the initial stage of the reaction and the ensuing surface etching of the urchin-like MnO2 by Br- produce hierarchical flower-like δ-MnO2 of 300 nm size. It has a three-dimensional mesoporous structure with a large surface area of 238 m2 g-1. It has an average pore size and pore volume of 36.14 Å and 0.567 cc g-1, respectively. The concentration of Br-1 controls the growth of δ-MnO2 and a large excess of Br-1 completely reduces MnO2 to Mn2+. The δ-MnO2 nanostructure shows excellent supercapacitive performance with a specific capacitance of 364 F g-1 at a current density of 1 A g-1. An aqueous asymmetric supercapacitor (ASC) is developed by pairing the δ-MnO2-based cathode with an activated carbon anode. ASC delivers a specific capacitance of 86.5 F g-1 at 1 A g-1 with a wide potential window of 0–2 V. It retains 100% initial specific capacitance even after 3000 continuous charge–discharge cycles. The device has an energy density of 48.06 W h kg-1 at the power density of 1.0 kW kg-1 and it retains 24.44 W h kg-1 at a power density of 20 kW kg-1. The favourable access of the electrode material to the electrolyte due to the mesoporous structure enhances the overall performance of the device
Covalent functionalization and electrochemical tuning of reduced graphene oxide for the bioelectrocatalytic sensing of serum lactate
No full textLactate is a byproduct of glycolysis and serum lactate can be used as a non-invasive biomarker in risk-stratifying patients with several life-threatening diseases. Herein, we describe the bioelectrocatalytic sensing of lactate using a covalently functionalized reduced graphene oxide (rGO)-based material. The development of a lactate biosensor involves the covalent functionalization of rGO with the p-nitrophenyl moiety, electrochemical generation of a surface-confined redox mediator and immobilization of L-lactate dehydrogenase (LDH). The covalently functionalized rGO was characterized by XRD, XPS, FTIR, Raman, resistivity and electrochemical measurements. The covalent attachment of the nitrophenyl moiety on the basal plane of the carbon network significantly influences the capacitive properties of rGO. The chemically functionalized rGO was electrochemically tuned to generate a redox mediator (rGO-PhNHOH). An electrochemically generated redox couple (PhNHOH/PhNO) exhibits reversible voltammetric response at ∼−0.06 V with a surface coverage of (7.19 ± 0.26) × 10−9 mol cm−2. The redox couple efficiently mediates the oxidation of NADH at 0.04 V, which is ∼600 mV less positive potential than the unmodified electrode. The electrode is highly sensitive towards NADH and it could detect as low as 0.4 μM NADH at the potential of 40 mV at neutral pH without any interference from co-existing bioanalytes. A lactate biosensor was developed using the rGO-PhNHOH functional material and lactate dehydrogenase. The surface-confined redox mediator could successfully detect the enzymatically generated NADH at 40 mV. The biosensor is highly sensitive (10.57 ± 0.38 nA μM−1 cm−2) and shows linear response up to 90 μM of lactate. It could detect lactate as low as 2.5 μM without any interference from other analytes. This biosensor has been successfully used to quantify human serum lactate and the results are in excellent agreement with those obtained by the clinical method
Simultaneous detection of ascorbic acid and dopamine at gold electrode modified with a self-assembled monolayer of cystamine
No full textThe electrochemical oxidation of ascorbic acid (AA) and dopamine (DA) at a gold electrode modified with a self-assembled monolayer (SAM) of cystamine (CYSA) has been studied. A large decrease in the overpotential for the oxidation of AA was noticed at CYSA-Au electrode. Well-separated square wave voltammetric peaks for AA and DA were observed at this electrode, which can be used for the simultaneous detection of these species
Carbon nanotube supported platinum nanoparticles for the voltammetric sensing of hydrazine
No full textElectrochemical sensing of hydrazine using a highly sensitive platform based on nanosized Pt (nPt) particles is described. The sensing platform is developed by the pre-organization of metal precursor on multiwalled carbon nanotubes (MCNT) modified conducting substrate and subsequent chemical reduction of the precursor in aqueous solution. The Pt nanoparticles are characterized by transmission electron microscope, X-ray diffraction (XRD), spectral and electrochemical measurements. The nPt on MCNT modified electrode has spherical shape with 5–10 nm size. XRD and selected area electron diffraction pattern reveal the existence of (1 1 1), (2 0 0) and (2 2 0) planes of face centered cubic structure. The electrocatalytic activity of nPt on the MCNT modified electrode toward oxidation of hydrazine is examined. The nPt on the MCNT modified electrode exhibit significantly high electrocatalytic activity with respect to the polycrystalline Pt electrode. The nanoparticle coverage on the electrode has strong influence on the electrocatalytic activity. Gradual negative shift in the oxidation peak potential and increase in the peak current are observed while increasing the particle coverage. The nanoparticle-based electrode is highly stable and sensitive and it can sense as low as 0.5 nM hydrazine sulfate at the potential of −0.35 V without any redox mediator. The co-existence of hydrazine derivative N,N-dimethylhydrazine does not interfere the electrochemical sensing of hydrazine
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