Showing papers on "Cyclic voltammetry published in 1988"
TL;DR: In this paper, the authors reported improvements in performance of PEM fuel cells utilizing electrodes with only one-tenth of this platinum loading by incorporating a proton conductor (Nafion) into the electrode structure.
Abstract: Proton exchange membrane (PEM) fuel cells showing promise of a high level of performance have, up to the present time, used electrodes containing a high platinum loading (4 mg/cm2). We report improvements in performance of PEM fuel cells utilizing electrodes with only one‐tenth of this platinum loading by (i) extension of the three‐dimensional reaction zone by incorporation of a proton conductor (Nafion) into the electrode structure; (ii) optimization of the amount of Nafion impregnated into the electrode structure; (iii) hot‐pressing the impregnated electrodes to the Nafion membrane at 120°C and 50 atm; (iv) optimal humidification of reactant gases at a temperature above that of the cell (5°C for or air and 10°–15°C for ); and (v) operation at elevated temperatures and pressures. The performance of the cells was analyzed from measurements of cell potential vs. current density and of cell potential at constant current density vs. time. Cyclic voltammetry proved to be a useful tool to ascertain the electrochemically active area of the electrodes.
547 citations
TL;DR: The redox processes of a glassy carbon electrode in THF were studied by programmed cyclic voltammetry in the range of +1300 to −2000 mV at sweep rates of 2-200 mV/s.
Abstract: The redox processes of at a glassy carbon electrode in THF was studied by programmed cyclic voltammetry in the range of +1300 to −2000 mV (vs. polysulfide reference electrode) at sweep rates of 2–200 mV/s. One anodic and up to three cathodic peaks were detected. The anodic peak seems to result from the oxidation of all PS's through the same intermediate to elemental sulfur. The first cathodic peak is caused by the reduction of all PS to in a diffusion controlled reaction. The second reduction peak most likely arises from the reduction of to . This is apparently preceded by a chemical step. The third reduction peak is caused by the reduction of to or S2− or a mixture of both in a diffusion‐controlled reaction. The high Tafel slope of the third peak apparently results from passivation of the electrode by the precipitation of and .
479 citations
TL;DR: In this article, the growth rate of polyaniline (PA) is characterized as autocatalytic and the electrochemical growth may be characterized as first order in aniline concentration, depending on the amount of PA film on the electrode and the number of potential cycles.
Abstract: Details of the growth properties of polyaniline (PA) have been studied employing electrochemical techniques (potential cycling method) and the results are reported. The electrochemical growth may be characterized as autocatalytic, and the growth rate is first order in aniline concentration. The growth rate is also dependent on the amount of PA film on the electrode as well as the number of potential cycles. The highest oxidized PA, attacked by an aniline molecule, grows to a longer chain, and a net reduction of the PA film upon aniline addition would render the film conducting. This mechanism explains why the film continues to grow at potentials where only passivating behavior would be predicted. In addition, the growth was divided into regions of well‐defined and poorly defined (amorphous) phases; at longer oxidation times during growth, side reactions seem to play more important roles compared to the earlier phase of the growth process.
461 citations
TL;DR: Some of the physical and chemical properties of polyaniline (PA) films have been studied and results are reported as discussed by the authors, including the density of PA sulfate (1.5 g/cm3), empirical equations relating the film thickness with electrical charges measured during the film growth, cyclic voltammetric peak potentials, or the amount of benzoquinone recovered after the degradation reaction, and spectral absorptivity of reduced PA at its absorption band maximum.
Abstract: Some of the physical and chemical properties of electrochemically grown polyaniline (PA) films have been studied and results are reported. Physical properties determined include the density of PA sulfate (1.5 g/cm3), empirical equations relating the film thickness with electrical charges measured during the film growth, cyclic voltammetric peak potentials, or the amount of benzoquinone recovered after the degradation reaction, and spectral absorptivity of reduced PA at its absorption band maximum ( depending on the medium). Elemental analysis results as well as stability factors determined during the potential cycling in various electrolyte solutions are presented as part of some chemical properties.
348 citations
TL;DR: In this article, the flat-band potential of the clean (001) Cd surface has been determined to about -1.8 V(SCE) in the dark.
Abstract: The photoelectrochemical behavior of cadmium sulfide depends strongly on the pretreatment of the electrodes. Sulfur, the main photocorrosion product of CdS, changes the potential drop across the Helmholtz double layer and shifts the flat-band potential of CdS in the anodic direction. Removal of sulfur from the surface is possible by prepolarizing the electrode at about -1.1 V(SCE) in the presence of oxygen. The flat-band potential of the clean (001) Cd surface has been determined to about -1.8 V(SCE) in the dark. Illumination of the electrode leads to surface-state charging due to formation of S/sup .-/, the intermediate in the formation of both possible photooxidation products: S/sup 0/ in the absence of oxygen and SO/sub 4//sup 2 -/ in the presence of oxygen.
333 citations
TL;DR: In this article, multilayer films of zirconium 1,10-decanediylbis(phosphonate) have been prepared on silicon and gold substrates and characterized by ellipsometry, XPS, and electrochemical measurements.
Abstract: Multilayer films of zirconium 1,10-decanediylbis(phosphonate) have been prepared on silicon and gold substrates and characterized by ellipsometry, XPS, and electrochemical measurements. The deposition technique requires first covalent attachment or adsorption of a phosphonic acid anchoring agent; HO(CH/sub 3/)/sub 2/Si(CH/sub 2/)/sub 3/PO/sub 3/H/sub 2/ (I) and (-S(CH/sub 2/)/sub 4/PO/sub 3/H/sub 2/)/sub 2/ (II) were used with Si and Au, respectively. The functionalized substrates are exposed alternately to aqueous ZrOCl/sub 2/ and 1,10-decanediylbis(phosphonic acid) solutions to yield multilayer films. Ellipsometry shows an increase in film thickness, on Si, of 17 A/layer, which corresponds to the layer spacing in bulk Zr(O/sub 3/PC/sub 10/H/sub 20/PO/sub 3/). Variable take-off angle X-ray photoelectron spectra from four-layer films have attenuated Si peaks but strong Zr and P peaks when the detector is 70/sup 0/ off the surface normal, implying that the films on Si are continuous. Electrochemical comparison of bare and functionalized Au shows facile electron transfer between Au or Au-II electrodes and 1 mM aqueous Fe(CN)/sub 6//sup 3 -/ but nearly complete blocking of electron transfer at Au-II electrodes immersed once each in ZrOCl/sub 2/ and 1,10-decanediylbis(phosphonic acid) solutions.
302 citations
TL;DR: In this paper, the cyclic potential sweep (CPS) method was applied to aniline electropolymerization in several strong acids (H 2 SO 4, HNO 3, HCl, HBF 4, HClO 4 and CF 3 COOH).
282 citations
281 citations
279 citations
TL;DR: In this article, it was shown that the intensity of the middle peak increases upon copolymerisation of the aniline with phenazine or m-phenylenediamine; this new polymer can be prepared in pure form by the oxidation of hydrazobenzene in NH4F·2.3 HF.
272 citations
TL;DR: The direct electrochemistry of redox proteins has been achieved at a variety of electrodes, including modified gold, pyrolytic graphite and metal oxides, and a new generation of electrochemical biosensors employs ferrocene derivatives as mediators.
Abstract: The direct electrochemistry of redox proteins has been achieved at a variety of electrodes, including modified gold, pyrolytic graphite and metal oxides. Careful design of electrode surfaces and electrolyte conditions are required for the attainment of rapid and reversible protein-electrode interaction. The electron transfer reactions of more complex systems, such as redox enzymes, are now being examined. The 'well-behaved' electrochemistry of redox proteins can be usefully exploited by coupling the electrode reaction to enzymes for which the redox proteins act as cofactors. In systems where direct electron transfer is very slow, small electron carriers, or mediators, may be employed to enhance the rate of electron exchange with the electrode. The organometallic compound ferrocene and its derivatives have proved particularly effective in this role. A new generation of electrochemical biosensors employs ferrocene derivatives as mediators.
TL;DR: In this paper, the electrodeposition of platinum microparticles into polyaniline (PA) films on glassy carbon (GC) electrodes and their catalytic activity for the reduction of hydrogen and the oxidation of methanol are described.
Abstract: The electrodeposition of platinum microparticles into polyaniline (PA) films on glassy carbon (gc) electrodes and their catalytic activity for the reduction of hydrogen and the oxidation of methanol are described. Electrodeposited platinum microparticles are dispersed in a three-dimensional array in fibril-type polyaniline film electrodes as evidenced by scanning electron microscope photomicrographs. These Pt/PA/gc electrodes exhibit good activity with respect to the catalytic reduction of hydrogen and the catalytic oxidation of methanol. Since polyaniline is a conducting polymer at potentials positive of 0.2 V vs Ag/AgCl, the PA films contribute a substantial amount of charge during the oxidation of methanol at 0.6 V. In addition, they also offer a protecting matrix for the Pt microparticles against particle loss and contamination from the bulk solution. The electrodes exhibited excellent long-term stability in the acidic methanol solutions.
TL;DR: In this article, the electrochemical behavior of a bismuth surface compound formed spontaneously without applying external potential when platinum is put in contact with a solution of a Bi(III) salt was studied.
TL;DR: In this paper, a surface analysis using x-ray photoelectron spectroscopy (XPS) combined with sputter profiling and Rutherford backscattering spectrometry (RBS) has been presented.
Abstract: Oxygen reduction in has been investigated at , and at surfaces produced from them by selective dissolution of the Cr component. Rotating disk electrodes (RDE) were used to examine the oxygen reduction reaction (ORR). The published (1–2) surface analysis using x‐ray photoelectron spectroscopy (XPS) combined with sputter profiling and Rutherford backscattering spectrometry (RBS) convincingly demonstrated that the surface region can be selectively depleted of the Cr component by electrochemical excursions to potentials positive of ~+1.25V vs. RHE. For the more Cr‐rich alloy very severe depletion (>500A) occurs upon prolonged potential excursions above +1.25V. For the sample, the surface depletion extends about 2–3 monolayers into the surface. Electrochemical characterization by cyclic voltammetry also confirms that the surface becomes progressively roughened as the potential exceeds the region where chromium is passive. Extensive roughening of the surface results in a significant increase of the measured ORR current per geometric area of the RDE. Tafel slopes of the ORR for moderately rough surfaces (roughness factor, ), produced from either starting alloy, are nearly identical to pure smooth Pt. For rougher surfaces (produced only at the more Cr‐rich starting alloy) the Tafel slopes determined from a mass‐transfer corrected plot of are also nearly identical to those obtained at smooth Pt. It is concluded that the measured increase of ORR current following the roughening of the RDE alloy electrode is due solely to the increase of Pt surface area. The mechanistic and practical implications of this effect in fuel cell electrochemistry are discussed.
TL;DR: In this paper, the authors used ellipsometry to monitor the growth of a glassy carbon electrode, which was electrochemlcally anodized at 1.8 V In 0.1 M H,SO.
Abstract: Ellipsometry was used to monitor the In situ growth of a fllm on a glassy carbon electrode, whlch was electrochemlcally anodized at 1.8 V In 0.1 M H,SO,. The layer grew contlnuously In an uninhlblted fashion wlth constant optical constants to a thlckness of at least 925 nm. It was nearly transparent at wavelengths of 545 and 632.8 nm. X-ray and elemental analysls of bulk quantltles of the phase Indicate that It Is an amorphous form of graphlte oxlde. Comblned elllpsometrlc and electrochemical measurements show that the phase activates the surface and that deactivation occurs upon extennslve reductlon of the layer. The electrode actlvlty, as monitored by the voltammetrlc response In dilute solutlons of catechol, hydroquhne, and 2,3-dlcyanohydroqulnone, varled wlth the extent of reductlon of the layer.
TL;DR: In this article, a polypyrrole containing the toluenesulphonate counter-ion has been electrochemically polymerized on a wide range of metallic electrodes, including platinum, titanium, aluminium, mild steel and brass.
TL;DR: In this article, metal particles were dispersed in electrically conducting polymer films in order to achieve multi-electron transfer processes in a three-dimensional matrix, and the electrocatalytic reduction of oxygen was investigated by rotating disk electrode studies with these films.
TL;DR: In this paper, surface-enhanced Raman scattering (SERS) signals were identified as arising from deuterium isotope data, in view of their absence for the reduced film when using smooth gold surfaces and/or green/blue laser excitation.
Abstract: Thin films of nickel hydroxide deposited on gold electrodes have been characterized in detail by in situ surface Raman spectroscopy in conjunction with electrochemical techniques. Raman spectra were obtained for film thicknesses varying from less than one equivalent monolayer to several hundred monolayers, as determined from the faradaic charge for the cyclic voltammetric oxidation of . For the thinnest films, Raman bands at 455 cm−1 and at 480 and 560 cm−1were obtained for the reduced and oxidized films, respectively, using 647.1 nm excitation at roughened gold. These signals, identified with Ni‐OH and Ni‐O vibrations from deuterium isotope data, were diagnosed as arising from surface‐enhanced Raman scattering (SERS) in view of their absence for the reduced film when using smooth gold surfaces and/or green/blue laser excitation. Raman spectra were obtained using the latter conditions for thicker oxidized films, which were consistent with resonance Raman scattering (RRS). Analysis of the dependence of the band intensities as a function of film thickness under conditions where SERS or RRS predominates enables the relative contributions of these mechanisms as well as the influence of film absorbance to be assessed quantitatively. Raman spectra were also obtained in air and after "film aging" by potential cycling or heating. The spectral changes following the latter treatments support the evolution of a less hydrogen‐bound film structure, i.e., the transformation of . By combining cyclic voltammetry with analysis of the dissolved film using atomic absorption spectroscopy, the effective oxidation state of nickel in the oxidized films is determined to be . On the basis of the spectroscopic and electrochemical measurements, the most likely structure for the oxidized film is a hydrated form of , where M is the supporting electrolyte cation.
TL;DR: In this article, a new soluble conducting polymer was found that promises to be useful both in understanding conducting polymer chemistry and in new industrial applications, which can be polymerized by both chemical and electrochemical methods and gives, using either method, a highly colored material with a conductivity of 3.0 S and good solubility in a number of inorganic and organic solvents.
TL;DR: In this article, the authors investigated cyclic voltammetry, energy dispersive X-ray analysis (EDX), XPS, ferric equivalent weight determination, and spectroelectrochemistry.
Abstract: Prussian blue (PB) films grown on Pt and SnO2 electrodes are investigated by cyclic voltammetry, energy dispersive X-ray analysis (EDX), XPS, ferric equivalent weight determination, and spectroelectrochemistry.
TL;DR: In this article, an electrochemical quartz crystal microbalance has been used to study the anodic electropolymerization of pyrrole and concurrent deposition of polypyrrole onto gold in acetonitrile and propylene carbonate using tetraethylammonium tosylate, tetrabutylammoniam tetrafluoroborate, and lithium perchlorate.
TL;DR: In this paper, the cyclic voltammetry of Pt (111) in three different structural states (well-ordered, restructured by electrochemical redox cycling, and restructuring by Ar+-sputtering) was studied in aqueous acidic and basic electrolytes using a UHV-electrochemical transfer system.
TL;DR: The action of cobalt on the characteristics of the nickel hydroxide electrode has been investigated by constant current, linear potential sweep and EDAX methods as mentioned in this paper, and it was found that cobalt raises the oxygen overpotential and promotes greater utilization of the active material.
Abstract: The action of cobalt upon the characteristics of the nickel hydroxide electrode has been investigated by constant current, linear potential sweep and EDAX methods. It was found that cobalt raises the oxygen overpotential and promotes greater utilization of the active material, although major additions of cobalt were observed to lower the working potential of the electrode. It was also found that cobalt prevented any significant loss of electrode capacity when the system was poisoned with iron.
TL;DR: In this article, the adsorption of hydrogen and sulphuric acid anions has been studied on single-crystal platinum stepped surfaces from the [110] zone, and the voltammetric profiles are in a wide potential range determined by bisulphate and sulphate adaption/desorption.
TL;DR: In this paper, the mutual dependence of the faradaic and double-layer charging currents is taken into account for the reduction of anthracene in dimethylformamide, a test example of very fast electron transfer kinetics (kSap = 3.5 cm s−1).