Daniel A. Scherson

An implantable biofuel cell for a live insect.

A biofuel cell incorporating a bienzymatic trehalase|glucose oxidase trehalose anode and a bilirubin oxidase dioxygen cathode using Os complexes grafted to a polymeric backbone as electron relays was designed and constructed. The specific power densities of the biofuel cell implanted in a female Blaberus discoidalis through incisions into its abdomen yielded maximum values of ca. 55 μW/cm(2) at 0.2 V that decreased by only ca. 5% after ca. 2.5 h of operation.

Transition metal macrocycles supported on high area carbon: Pyrolysis—mass spectrometry studies

Abstract A number of cobalt and iron porphyrins heat treated at temperatures as low as 400°C exhibit substantial electrocatalytic activity for O 2 reduction and reasonable stability in alkaline electrolytes. The effects of this heat treatment on the structure and overall properties of these materials, however, are not well understood. Differential thermogravimetry analyses have shown that in the case of the Co and Fe-μ-oxo forms of tetra methoxyphenyl porphyrin (TMPP) and the metal-free form as well, the onset for partial decomposition occurs at temperatures of about 400–500°C for the macrocycles either as crystals or dispersed on high area Vulcan XC-72. The results obtained with several pyrolysis—mass spectrometric techniques have indicated that the fraction of volatile nitrogen to non-nitrogen containing species generated during the heat treatment is much higher for the metal-free than for the iron-μ-oxo or CoTMPP. Microanalysis also confirms that with the Fe-μ-oxo and CoTMPP part of the nitrogen is retained. Possible models for the nature of the active sites are discussed.

Cobalt tetramethoxyphenyl porphyrin—emission Mossbauer spectroscopy and O2 reduction electrochemical studies

Abstract Cobalt tetramethoxyphenyl porphyrin (Co-TMPP) on a high area carbon support after thermal treatment at 450–900°C has been found to be an effective catalyst for O2 reduction in alkaline electrolytes. The effect of the heat treatment at 850°C on this catalyst has been examine with emission Mossbauer spectroscopy using Co-57 enriched Co-TMPP. The spectra indicate the presence of cobaltous oxides with no evidence of Co-N4 centers or any other form of cobalt. The metal-free complex H2TMPP, given similar thermal treatment on a mineral-free carbon support does not show catalytic activity beyond that of the carbon support, thus confirming the importance of the transition metal to the catalysis.

In Situ Quartz Crystal Microbalance Studies of Nickel Hydrous Oxide Films in Alkaline Electrolytes

The microgravimetric characteristics of electrodeposited nickel and composite Ni/Co hydrous oxide films on Au electrodes in KOH electrolytes were examined in situ with a combination of quartz crystal microbalance (QCM) and voltammetric techniques. In the case of freshly prepared {alpha}-Ni(OH){sub 2} hydrous oxide films, denoted as {alpha}-Ni(OH){sub 2}(hyd), the mass increased during oxidation and then decreased upon subsequent reduction. As the redox cycling was continued, however, this behavior gradually reversed, i.e., the mass decreased upon oxidation and then increased following further reduction. This unique effect could be correlated with a shift in the position of the oxidation peak maximum (E{sub p}{sup ox}) in the voltammogram toward more positive potentials, which has been ascribed to the transformation of {alpha}-Ni(OH){sub 2}(hyd) into {beta}-Ni(OH){sub 2}(hyd). Based on these findings, it can be concluded that the mechanism of ionic charge transport in these two types of lattices is markedly different. In contrast, composite Ni/Co (9:1) hydrous oxide films displayed qualitatively the same behavior as pure freshly prepared Ni(OH){sub 2}(hyd) in the same alkaline media regardless of the extent of cycling. This observation provides evidence that the incorporation of cobalt into Ni(OH){sub 2}(hyd) modifies the structural properties of the lattice during the oxidation/reduction process.

Spectroscopic techniques for the study of solid–liquid interfaces

Substantial progress has been made with in‐situ use of optical reflectance spectroscopy and Raman spectroscopy in studies of the properties of solid–liquid interfaces and particularly metal– and semiconductor–electrolyte interfaces. Such techniques provide molecular level information concerning adsorbed species and various thin films not available from electrochemical and other measurements. Ex‐situ techniques including electron and ion spectroscopies also have proved helpful in understanding the properties of solid–liquid interfaces but special techniques are necessary to minimize changes in the surface structure of the solid during the transfer between the liquid and ultrahigh vacuum environment. Some of the results obtained recently by various workers using such transfer techniques in the study of adsorption on single crystals at electrochemical interfaces will be reviewed. For adsorption on some solid surfaces there is parallel behavior in the liquid and vacuum environments and comparison affords insi...

The Electrocatalytic Reduction of Nitrate Mediated by Underpotential‐Deposited Cadmium on Gold and Silver Electrodes in Acid Media

This paper reports rotating ring-disk electrode techniques employed for the investigation of the electrocatalytic reduction of nitrate induced by underpotential-deposited cadmium on Au and Ag surfaces. Based on Alberys kinetic analysis it has been concluded that for concentrations of nitrate in the millimolar range, the reaction products depend on the {ital p}H of the solution. Specifically, for {ital p}H = 3, the reaction yields predominantly nitrite, whereas for {ital p}H = 1, the process proceeds beyond the nitrite stage to generate products which do not undergo oxidation on a Au ring electrode polarized at potentials as high as 1.0V {ital vs.} SCE. Additional evidence in support of these results was provided by exhaustive bulk electrolysis experiments. The lack of linearity of some of Alberys diagnostic plots could be accounted for quantitatively by a numerical integration of the differential equations which govern disproportionation-type reactions at rotating ring electrodes. Good agreement was found between theory and experiment using independently determined values for the rate constant of disproportionation of NO{sub 2} in solution.

Electrochemical characterization of lithiated transition metal oxide cathode particles in the absence of carbon, binders and other additives

Abstract A novel method is herein described for the electrochemical characterization of lithiated transition metal oxides in powder form as cathode materials for lithium ion batteries. The procedure involves application of sufficiently high pressures to a layer of oxide powder evenly dispersed on the surface of a Au foil so as to embed the particles into the soft metal substrate, thereby avoiding the use of carbon, binders and other additives. Implementation of this methodology for battery-grade LiMn2O4, LiCoO2 and LiCo0.15Ni0.85O2 particles supplied by various commercial sources yielded electrodes of excellent mechanical integrity displaying close to ideal cyclic voltammetric behavior in electrolytes of relevance to battery applications. The charge capacity of each of these compounds could be estimated quantitatively by dissolving the array of oxide particles in acid, once the electrochemical experiments were completed and then determining the amount of metal in the solutions by ICP-MS analysis. An analysis of voltammetric measurements as a function of scan rate yielded values of mean diffusion coefficients for Li in LiMn2O4 on the order of 5×10−10 cm2 s−1.

Perovskite-type oxides - Oxygen electrocatalysis and bulk structure

Perovskite type oxides were considered for use as oxygen reduction and generation electrocatalysts in alkaline electrolytes. Perovskite stability and electrocatalytic activity are studied along with possible relationships of the latter with the bulk solid state properties. A series of compounds of the type LaFe(x)Ni1(-x)O3 was used as a model system to gain information on the possible relationships between surface catalytic activity and bulk structure. Hydrogen peroxide decomposition rate constants were measured for these compounds. Ex situ Mossbauer effect spectroscopy (MES), and magnetic susceptibility measurements were used to study the solid state properties. X ray photoelectron spectroscopy (XPS) was used to examine the surface. MES has indicated the presence of a paramagnetic to magnetically ordered phase transition for values of x between 0.4 and 0.5. A correlation was found between the values of the MES isomer shift and the catalytic activity for peroxide decomposition. Thus, the catalytic activity can be correlated to the d-electron density for the transition metal cations.

Underpotential Deposition of Aluminum and Alloy Formation on Polycrystalline Gold Electrodes from AlCl3 / EMIC Room‐Temperature Molten Salts

Interfacial processes occurring at polycrystalline gold in acidic 1-ethyl-3-methylimidazolium chloroaluminate melts at room temperature, at potentials more positive than aluminum bulk deposition, include both Al underpotential deposition and the formation of Al/Au alloys. This information complements that reported in the literature for Al electrodeposition on Au in AlCl{sub 3}/NaCl melts at temperatures of 200 C and higher. Cyclic voltammetry and chronopotentiometry suggest that at least two alloys form, and there is fast phase transformation between these intermetallic compounds at room temperature in the aluminum underpotential region. This transformation with thin gold films was slower than that in bulk gold electrodes.

Oxygen reduction on adsorbed iron tetrapyridinoporphyrazine

Abstract The electrocatalytic properties of iron tetrapyridino porphyrazine FeTPyPz for the reduction on O2 in alkaline media have been examined with cyclic voltammetry and rotating ring disk techniques. Four distinct redox peaks are observed in the absence of O2 in solution for this material adsorbed at monolayer coverages on ordinary pyrolytic graphite surfaces. The onset for O2 reduction appears to coincide with the voltammetric peak associated with the metal centered Fe(II)TPyPz/Fe(III)TPyPz transition. No hydrogen peroxide is detected at the ring in this potential range indicating that the reaction takes place by a four electron pathway. This is in contrast with the behavior observed at more negative potentials for which sizable currents for H2O2 oxidation are observed. This change in the mechanism has been attributed to the further reduction of the iron center in the macrocycle rendering an Fe(I)TPyPz species. If the electrode is polarized at potentials more negative than −0.8 V vs SCE, however, the reduction proceeds once again without generation of H2O2 in the solution phase. Quantum mechanical arguments involving orbital symmetry and overlap indicate that the activation could involve a simultaneous bonding of O2 to the iron center and a bridge nitrogen in the macrocycle ring. Such a potential dependent mechanism is similar to that reported earlier for iron tetrasulfonated phthalocyanine for which theoretically predicted electronic properties are essentially the same as those of FeTPyPz.