Multi-scan Cyclic Voltammetry Research Articles

Manipulation of flexible carbon cloths for stable and efficient catalysts in dye-sensitized solar cells

• The CC with preferred characteristics can be facilely manipulated. • The catalytic activity and stability of CE can be improved via underlying supports. • The simultaneously improved PCE and stability are achieved by using an optimal CE. The highly stable and efficient dye-sensitized solar cell (DSC) strongly relies on the catalytic activity and stability of the counter electrode (CE) in the electrolyte. Herein, we explore an effective and eco-friendly method of making a high catalytic activity of CE with the improved stability by utilizing the high-conductivity carbon cloth (CC) with great corrosive resistance as flexible carbon-based supports for nanoparticle-based catalysts and using Pt as an example. A variety of CCs with different characteristics are facilely manipulated by the hybrid solution-based surface treatments, enabling to systemically investigate the influence of different CCs on the performance of Pt catalysts. The result shows that the surface activated CC with properly porous structure and wetting surface facilitates the accommodation of catalysts and the diffusion of redox couple within the carbon fiber network. The existence of active sites such as defective structures and oxygen-containing groups on CCs effectively serve as the nucleation or adsorbed sites of Pt catalysts, which simultaneously improve the catalytic and stable performance of CE. Multi-scan cyclic voltammetry indicates that a preferred surface activated CC as Pt catalyst support retains 95.9% of its initial catalytic ability in comparison with the typical platinized fluorine-doped tin oxide (76%). The DSC using the desirable Pt-decorated CC displays an improvement of 49% in conversion efficiency as compared with that using the nonoptimal counterpart. Such improvements highlight the feasibility of simply manipulating the characteristics of underlying flexible carbon-based supports in pursuit of the high catalytic activity and stability of CEs in DSCs.

Multi-scan cyclic voltammetry of a solution containing mixed valence states

When both members of a redox pair are present in a voltammetric cell, the applied signal must start at the null potential if pure cyclic voltammetry is to be conducted. Here the current from a limitless number of repetitive cyclic scans is predicted mathematically for any initial reductant to oxidant ratio. The predictions were prompted by, and are compared with, published experiments. Some simplifying conditions are imposed: the reaction is reversible; the redox pair share the same diffusivity; the reversal potentials are symmetrically disposed with respect to the halfwave potential.

Experimental and DFT investigation of 3D-HBGP/Pt/Co as a superb electrocatalyst for methanol oxidation reaction

Abstract Three-dimensional hollow balls of graphene oxide and polyaniline (3D-HBGP) nanocomposite were constructed by the self-assembly of graphene oxide (GO) and the polymerization of polyaniline (PANI) on poly(methyl methacrylate) (PMMA) particles. The 3D-HBGP was utilized as the support catalyst for platinum–cobalt (Pt–Co) that was electrochemically deposited on its surface for methanol oxidation reaction. Electrochemical measurements illustrates that the peak current density of 3D-HBGP/Pt/Co is 22.53 mA/cm2, which is 2.48 higher than Pt–Co alloy without 3D-HBGP support. According to this observation, the electro-catalytic activity of 3D-HBGP/Pt/Co is higher than that of Pt–Co electrocatalyst for methanol oxidation reaction (MOR). Compared to Pt–Co electrocatalyst, the electrochemical active surface area (ECSA) of 3D-HBGP/Pt/Co increases to 20.38 m2/g during cyclic voltammetry (CV) test. In addition, multi-scan cyclic voltammetry indicates that the 3D-HBGP/Pt/Co electrocatalyst has great catalytic stability for MOR. The density functional theory (DFT) calculation results reveal that utilizing the 3D-HBGP structure alongside Pt and Co leads to decreasing of the energy gap and increasing of the reactivity of catalyst which is in good agreement with experimental findings. The current study results (performance and stability) illustrate that the fabricated 3D-HBGP/Pt/Co electrocatalyst can be a prospective anode catalyst for direct methanol fuel cell (DMFC).

Investigation of electrocatalytic activity and stability of Pt anode catalyst on the electrooxidation of 1,2-propanediol, 2-propanol and methanol in alkaline media

Carbon-supported platinum nanoparticles are successfully synthesized and characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). Electrocatalytic activity and stability of the Pt/C catalyst for 1,2-propanediol, 2-propanol and methanol electrooxidation was investigated using cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). According to the obtained results, the activity of the Pt/C catalyst for 1,2-propanediol oxidation reaction was higher than that of the other alcohols. Multi-scan cyclic voltammetry after 100 CV cycles revealed that the Pt/C catalyst has great catalytic activity, high poison-tolerance ability and improved electrochemical stability for 1,2-propanediol oxidation compared with methanol and 2-propanol. This indicates a lower poisoning effect of the adsorbed intermediates on the Pt/C performance in 1,2-propanediol oxidation. Infrared spectroscopy measurements after 100 CV cycles in methanol oxidation indicated that adsorbed CO specie is detected on the surface of Pt/C catalyst, but not in 1,2-propanediol oxidation. Comparison of the corresponding EIS measurements after 1st and 100th cycles showed that 1,2-propanediol has the best performance in terms of charge transfer resistance and specific capacitance.

Room temperature synthesis of Pd–Cu nanoalloy catalyst with enhanced electrocatalytic activity for the methanol oxidation reaction

Bimetallic Pd–Cu nanoparticles with controllable size, composition and superior electrocatalytic activity towards methanol oxidation reaction (MOR) in alkaline media were synthesized by a facile room temperature soft chemical method. Pd–Cu nanoalloy catalysts (17–25nm) were prepared by templating Pd2+ and Cu2+ with ethylenediaminetetraacetic acid (EDTA) followed by controlled chemical reduction of metal–EDTA complex with hydrazine in highly basic medium at room temperature without any protection with an inert gas atmosphere. X-ray diffraction pattern indicates that the particles have an alloy structure. FESEM, EDX, HRTEM and SAED results further support the formation of Pd–Cu nanoalloy. Compliance of the lattice spacing corresponding to (111) and (200) planes obtained from HRTEM and SAED results with XRD data confirms the formation of Pd–Cu nanoalloy at room temperature. By varying the Pd2+/Cu2+ molar ratio the compositions of these alloy NPs can be easily adjusted. The amount of Cu present in the Pd–Cu nanoalloy plays a key role on the catalytic activity for MOR in alkaline media. Upon increase in concentration of Cu in the Pd–Cu nanoalloy, the catalytic activity towards MOR increases, reaches a maximum in Pd–Cu(3:1) nanoalloy and then decreases. The maximum mass activity of 659.4mAmg−1 of Pd obtained in the present work for the synthesized Pd–Cu(3:1) nanoalloy is much better than literature reported value. Multi-scan cyclic voltammetry and chronoamperometric studies confirm the electrocatalytic activity and stability of the synthesized electrode material. The present catalyst with low noble metal content promotes its practical use as anodes under alkaline conditions in direct methanol fuel cells (DMFC).

One-step facile synthesis of Pd nanoclusters supported on carbon and their electrochemical property

Well-crystallized Pd nanoclusters supported on Ketjen Black (KB) were successfully fabricated when Pd wires were served as an electrode pair by a solution plasma technique at atmospheric pressure. The synthesis of Pd nanoclusters was almost simultaneous with their dispersion on KB. Pd nanoclusters with the average diameter of about 2nm were equably distributed on KB, and showed good electrochemical property corresponding to their obvious characteristic peaks. Multi-scan cyclic voltammetry and chronoamperometry clarified that as-prepared Pd nanoclusters have better electrochemical stability in alkaline solution than that of in acidic solution. Thus as-obtained Pd nanoclusters would become a promising electrocatalyst for fuel cells or Li-air batteries.

One-step facile synthesis of carbon-supported PdAu nanoparticles and their electrochemical property and stability

Well-crystallized PdAu nanoparticles supported on Ketjen Black (KB) were successfully fabricated when both Pd and Au wires were served as the electrode pair by a solution plasma technique at atmospheric pressure. The synthesis of PdAu nanoparticles was almost simultaneous with their dispersion on KB. As-obtained PdAu nanoparticles were confirmed to be alloy by ultraviolet–visible spectrophotometer, transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX) of each particle. PdAu nanoparticles with the average diameter of 2–5nm were equably distributed on KB. PdAu nanoparticles showed good electrocatalytic activity both in acidic and alkaline solution corresponding to their obvious oxidation and reduction features. PdAu nanoparticles have improved electrochemical stability compared with the electrochemical properties of Pd and Au nanoparticles mixture after long time multi-scan cyclic voltammetry. Multi-scan cyclic voltammetry also presented the PdAu nanoparticles in alkaline solution have better stability than that in acidic solution. Thus as-obtained PdAu alloy nanoparticles would become a promising electrocatalysts for fuel cells or Li-air batteries. This novel process showed its potential applications in designing optimization of catalysts for fuel cells or Li-air batteries in future.

Ultimate cyclic voltammetry: an analytical examination of the reversible case

Multi-scan cyclic voltammetry may lead eventually to a repetitive current-versus-potential graph. Here such “ultimate” cyclic voltammograms are investigated mathematically for reversible electrode reactions. The voltammetric shapes, after an infinite number of cycles, are modelled and their characteristics are documented. It is predicted that the approach to truly repetitive behaviour, within an experimentally realistic length of time, requires that a specific condition—balancing the potential scan range to the initial concentrations—be satisfied.

Multi-scan reversible cyclic voltammetry: is the ultimate condition approached and, if so, how fast?

A previous article shows that, after an infinite number of cycles, reversible cyclic voltammetry will attain an ultimate state characterized by properties that were identified in that study. Here, reversible multi-scan cyclic voltammetry has been modelled with a view to assessing the circumstances under which the ultimate state is attainable in an experimentally realistic time. The prediction has been confirmed that, under very specific conditions, the ultimate condition is attained after only a few scans. Under less restrictive conditions, one property of ultimacy is developed rapidly, but others evolve more slowly, or not at all. Modelling shows that the multi-scan voltammetric current may be analyzed into several components, of which the ultimate current is the purely periodic component.

Preparation and Selected Properties of an Improved Composite of the Electrophoretically Deposited Single-Wall Carbon Nanotubes, Electrochemically Coated with a C60-Pd and Polybithiophene Mixed Polymer Film

An improved carbon nanotube conducting composite material for electrochemical capacitors has been devised and tested. It was prepared by electrophoretic deposition of a film of noncovalently surface modified with 1-pyrenebutyric acid HiPCO single-wall carbon nanotubes (pyr-SWCNTs), which were then electrochemically coated, under multiscan cyclic voltammetry (CV) conditions, with a mixed film of the fullerene-palladium (C60-Pd) polymer and the polybithiophene (PBT) polymer. Both the electrophoretic deposition of pyr-SWCNTs and electrochemical polymerization of (C60-Pd)-PBT was in situ monitored by piezoelectric microgravimetry (PM) with the use of an electrochemical quartz crystal microbalance (EQCM). Atomic force microscopy imaging of the film revealed that pyr-SWCNTs formed tangles of pyr-SWCNTs bundles surrounded by globular clusters of (C60-Pd)-PBT. X-ray photoelectron spectroscopy provided information on the mole ratio of BT/C60/Pd ≈ 1:2:4 indicating that, most likely, the C60-Pd and PBT polymers are ...

Conductive, Capacitive, and Viscoelastic Properties of a New Composite of the C60−Pd Conducting Polymer and Single-Wall Carbon Nanotubes

Thin films of a new composite of an electroactive fullerene-based (C60-Pd) polymer and HiPCO single-wall carbon nanotubes, which were noncovalently modified by 1-pyrenebutiric acid (pyr-SWCNTs), were electrochemically prepared under multiscan cyclic voltammetry conditions. With respect to blank polymer, superior conductive, capacitive, and viscoelasitic properties of the composite were demonstrated. Composition of pyr-SWCNTs was determined by thermogravimetric analyses, which showed one molecule of 1-pyrenebutiric acid per approximately 20 carbon atoms of SWCNT. Atomic force microscopy imaging revealed that pyr-SWCNTs form tangles of pyr-SWCNTs bundles surrounded by globular clusters of the C60-Pd polymer. Peaks characteristic of both pyr-SWCNTs (radial breathing modes at approximately 200 to 300 cm(-1)) and C60-Pd polymer in the Raman spectra recorded for the composite confirmed the presence of pyr-SWCNTs in the composite film. The mass of the deposited film was in situ measured by piezoelectric microgravimetry with the use of an electrochemical quartz crystal microbalance (EQCM). Then, curves of the current, resonant frequency change, and dynamic resistance change versus the potential in different potential ranges were simultaneously recorded in a blank acetonitrile solution of tetrabutylammonium perchlorate. Specific capacitance, determined at -1.20 V for the composite as 90 F g(-1), was twice as high as that for the polymer. Electrochemical impedance spectroscopy was used to determine impedance parameters of both the C60-Pd polymer and C60-Pd/pyr-SWCNTs composite film. This data analysis indicated increased capacitance and decreased resistance for the new composite film.

Mechanistic studies of the electrochemical polymerization of C60 in the presence of dioxygen or C60O

Electropolymerization of C60 in the presence of dioxygen, in a mixture of acetonitrile and toluene (1 : 4, v : v) containing tetra(alkyl)ammonium perchlorate, was investigated by multi-scan cyclic voltammetry and piezoelectric microgravimetry with the use of an electrochemical quartz crystal microbalance. The fullerene was readily electropolymerized if the O2 to C60 concentration ratio in solution exceeded 1 : 10 and the applied potential reached values where electro-reduction of dioxygen to superoxide, O2˙−, and C60 to C602− occurred. The redox activity of the polymer was determined by cyclic voltammetry for solutions with different tetra-(alkyl)ammonium perchlorates used as supporting electrolytes. The film conductivity was higher the smaller the size of the cation in the supporting electrolyte. The C60 electropolymerization in the presence of dioxygen was suppressed when a spin trapping agent, N-tert-butyl-α-(4-nitrophenyl)nitrone that could intercept superoxide, was present. The fullerene was also electropolymerized in the presence of small amounts of the epoxide, C60O, in the absence of dioxygen. We postulate that the C60 electropolymerization in the presence of O2 proceeds via the initial nucleophilic attack of superoxide on C60 to form a C60O2˙− radical anion, which then interacts with another molecule of C60 to produce C60O and C60O˙−. Under further electro-reduction, these intermediates serve to initiate polymerization of C60 through the formation of C60O2−, as determined earlier in studies of the electropolymerization of C60O itself.

Reactivities of Organic Phase Biosensors 3: Electrochemical Study of Cytochrome P450cam Immobilized in a Methyltriethoxysilane Sol-Gel

A composite amperometric biosensor was prepared by encapsulating a cytochrome P450cam/didodecyldimethylammonium bromide (DDAB) liquid crystal system in a methyltriethoxysilane (MTEOS) sol-gel (SG). The composite sensing layer was cross-linked unto a 0.071 cm2 glassy carbon electrode (GCE) using glutaraldehyde. The electrochemical characteristics of the GCE-[P450cam/DDAB/SG] biosensor were studied by multiscan cyclic voltammetry in aqueous phase (0.05 phosphate buffer pH 7.3) and organic (CH3CN : H20; 90 % : 10 %) phase anaerobic media. Analysis of the cyclic voltammetric results show that the sensor exhibited faster reversible electrochemistry in the organic phase than in the aqueous phase. The cyclic voltammetric peak separation, ΔEp, values estimated for the buffer and acetonitrile media were 62 mV and 104 mV, respectively. The sol-gel-based sensor had a life-time of 4 weeks when stored at 4 °C, and was stable up to 45 °C, which is also the temperature of optimal sensor activity.

Formation of Redox-Active, Two-Component Films by Electrochemical Reduction of C60and Transition Metal Complexes

Electrochemical reduction of C60 in 4:1 toluene/acetonitrile solution in the presence of (PhCN) 2- PdCl2, Ir(CO)2Cl(p-toluidine), or (CF3CO2)4Rh2 produces three different, redox-active, black films that coat the electrode. These films are insoluble in common organic solvents and adhere strongly to the electrode surface. Film formation has been monitored by multiscan cyclic voltammetry, which gives information about the requirements for film growth. The three different films (on the original electrodes) can be transferred to a solution of acetonitrile that contains only the supporting electrolyte, tetra( n-butyl)ammonium perchlorate, where the films retain their redox activity. Each film displays a significant decrease in resistivity ( i.e. a window of conductivity) in the potential region in which it is grown and in which it displays redox activity. The films have been examined by scanning electron microscopy, which shows variations in the nature of the three films' morphologies with the film formed from (PhCN)2PdCl2 displaying the greatest uniformity and smoothest surface. Analysis of the films by infrared spectroscopy and laser desorption mass spectrometry reveals that intact C 60 units are present within each film. Treatment of the palladium/C60 film with triphenylphosphine results in film dissolution and the formation of the previously characterized complex, ( 2 -C60)Pd(PPh3)2. The rhodium/ C60 film dissolves in pyridine and 19 F{ 1 H} NMR spectroscopy reveals that (CF3CO2)4Rh2 is extracted intact from the film. The structure of the films is discussed in terms of covalent bonding between the fullerenes and the metal atoms or complexes within the film.

A pyrolysis mass spectrometry study of polythiophene — Natural rubber and polythiophene — Synthetic rubber conducting polymer composites

The thermal behaviors and degradation products of conducting polymer composites prepared by electrooxidation of thiophene using natural rubber or synthetic rubber as the insulating matrix were studied by direct and indirect mass spectrometry techniques. The pyrolysis mass data revealed that a chemical interaction formed between the components of the composites during polymerization. Thermal characteristics of rubbers totally disappeared in the composites indicating presence of some chain scissions leading to degradation of rubbers during electrooxidative polymerization. The multiscan cyclic voltammetry runs showed that polythiophene is also electroactive on the rubber coated metal electrodes, with a small shift in the redox peaks compared to the one on the bare electrode.