Perovskite-type oxides have been considered for use as oxygen reduction and generation electrocatalysts in alkaline electrolytes This paper is concerned with perovskite stability and electrocatalytic activity, and the possible relationships of the latter with the bulk-solid state properties. Perovskite oxides have not been found in general to be very active for oxygen reduction, although substantial catalytic activity for hydrogen peroxide decomposition has been found. Instability of some perovkites has been observed over particular potential ranges. In some cases these ranges overlap those in which 02 reduction occurs. A series of compounds of the type LaFexNil_xO 3 has been used as a model system to gain information on the possible relationships between surface catalytic activity and bulk structure. Hydrogen peroxide decomposition rate constants have been measured for these compounds. Exsitu Mossbauer effect spectroscopy (MES), and magnetic susceptibility measurements have been used to study the solid state properties. X-ray photoelectron spectroscopy (XPS) has been 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. For 0 < x s 0.4 the compounds are paramagnetic, as indicated by the absence of a Zeeman effect in the MES spectra. For 0.5 s x S 1.0 the observed Zeeman effect in the MES spectra indicates the presence of a magnetically ordered phase. Complementary magnetic susceptibility measurements indicate that the compounds are antiferromagnetically ordered. MES also shows that the introduction of Ni into the Fe(lll) matrix of LaFeO 3 forces some of the Fe(lll) into the unusual Fe(IV) state, while part of the Ni(lll) is changed to Ni(ll), as indicated by XPS. The hydrogen peroxide decomposition rates have been found to undergo a substantial change in the range 0.25 < x < 0.5. A correlation has been 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.

In developing advanced fuel cells and other electrochemical reactors, it is desirable to combine the advantages of solid polymer electrolytes with the enhanced catalytic activity associated with temperatures above 100-degrees-C. This will require polymer electrolytes which retain high ionic conductivity at temperatures above the boiling point of water. One possibility is to equilibrate standard perfluorosulfonic acid polymer electrolytes such as Nafion(TM), with a high boiling point Bronsted base such as phosphoric acid. The Nafion/H3PO4 electrolyte has been evaluated with respect to water content, ionic conductivity and transport of oxygen, and methanol vapor. The results show that at elevated temperatures reasonably high conductivity (>0.05 OMEGA-1 cm-1) can be obtained. Methanol permeability is shown to be proportional to the methanol vapor activity and thus decreases with increasing temperature for a given methanol partial pressure. Comparisons and distinctions between this electrolyte and pure phosphoric acid are also considered.

Oxygen reduction on bright platinum in concentrated H3PO4 has been investigated with the rotating disc electrochemical technique at temperatures from 25 to 250° C and oxygen pressures up to 1.77 MPa. Cyclic voltammetry has been employed to study the anodic film formed on platinum in concentrated H3PO4 and the possible electroreduction of H3PO4 on platinum. The apparent transfer coefficient for the oxygen reduction has been found to be approximately proportional to temperature rather than independent of temperature. Such behaviour is difficult to reconcile with accepted theories for the effect of electrode potential on the energy barriers for electrode processes. It is of importance to establish an understanding of this phenomenon. Possible factors which can contribute to the temperature dependence of the transfer coefficient but which would not necessarily result in a direct proportionality to temperature include potential dependent adsorption of solution phase species, restructuring of the solution in the compact layer, proton and electron tunnelling, a shift in rate-determining step, changes in the symmetry of the potential energy barrier, penetration of the electric field into the electrode phase, insufficient correction for ohmic losses, and impurity effects.

Copper, lead and carbon monoxide adsorbates have been used to probe the adsorption processes on a Pt(111) electrode in H2SO4 and HClO4 solutions. All three adsorbates cause inhibition of hydrogen adsorption in both solutions and a decrease of the anomalous peak recently ascribed to HSO4− adsorption. The “butterfly” peak in HClO4 solution is slightly perturbed by Cu and Pb adatoms. Evidence was found that the species responsible for the anomalous peak for Pt(111) in H2SO4 solutions is not Hads and that HSO4− probably interacts with three Pt(111) sites. A twofold interaction of HSO4− with the Pt(111) surface, however, cannot be ruled out completely. In HClO4 solutions the Cu and Pb adatoms do not cause any decrease of the charge associated with the “butterfly” peak. These results can be explained in terms of PtOH as the species involved with the “butterfly” peak. The electrosorption valence of HSO4ads− is unity, which indicates a strong interaction with the surface and a high charge transfer. The Temkin interaction parameter for Hads is fRT = 42 kJ mol−1, which provides evidence for a large repulsive interaction of Hads on the Pt(111) surface. It decreases in the presence of Cu and CO adsorbates. These results illustrate the usefulness of the competitive adsorption of various adsorbates in probing adsorption processes on electrode surfaces.

The electrochemical behavior of various non-aqueous organic electrolyte systems has been investigated using inert metal electrodes. The systems studied included propylene carbonate, dimethoxyethane and tetrahydrofuran solutions of LiClO4, LiAsF6, LiSO3CF3 and Bu4NClO4. The electrode metals included polycrystalline gold and silver. Various techniques including cyclic voltammetry, FTIR and XPS were used to characterize the main electrochemical reactions that occur in these systems. Several separate film forming processes have been identified, including reduction of solvent, the salt, and traces of oxygen and water. The surface films formed in these processes lead to the apparent stability of these systems at low potentials. Li UPD was also examined and was found to be controlled by the nature of the surface films through which lithium is deposited.

In order to obtain further insight into the redox properties and the oxygen reduction electrocatalysis on macrocycles, the effect of cyanide, capable of coordinating with the transition metal in the axial position, has been examined. These studies have been conducted with Fe- and Co-tetrasulfonated phthalocyanines adsorbed at the monolayer level on an ordinary pyrolytic graphite (OPG) rotating disk electrode. Fe and Co tetramethoxyphenyl porphyrins adsorbed on Vulcan XC-72 carbon at monolayer coverages have also been examined in 0.1 M NaOH in the form of a thin porous coating on an OPG disk with Teflon as the binder. The major focus has been on the blocking of the axial positions of the transition metal with CN− and the resulting effects on the redox couples as well as on O2 reduction. The data indicate that a strong axial interaction of O2 with the transition metal in the macrocycle is an important factor for O2 electrocatalysis. These blocking effects confirm the assignment of the peaks in cyclic voltammetry curves and the importance of particular redox couples to the O2 electrocatalysis.

The adsorption of iron and cobalt terasulfonated phthalocyanines (TsPcs) on ordinary pyrolytic graphite has been investigated as a function of pH and ionic strength of the adsorption solution as well as the potential. The charge corresponding to the voltammetric redox peaks of adsorbed complexes was used as a measure of the surface concentration. Adsorption of CoTsPc occurs readily from its freshly prepared aqueous solutions and is generally independent of pH. For FeTsPc, however, adsorption does strongly depend on pH. High surface coverage is achieved only from acid solutions rather than from pure water and alkaline solutions. This can be explained in terms of the form(s) of the complexes existing in the solution phase in the presence of air. uv-Visible spectroscopic studies coupled with the addition of CN− to the macrocycle solutions provide evidence that in pure water and alkaline solutions FeTsPc exists predominantly in the μ-oxo form (FeTsPc)2O, which seems not to favor the adsorption process. No evidence of the μ-oxo complex was found for FeTsPc in acid solutions and CoTsPc in aqueous solutions over the pH range examined (1–13). The adsorption of FeTsPc was at maximum when the potential was held at −0.55 V vs sce in 0.1 M NaOH.

The oxidation of α-D(+)-glucose on a platinum electrode in 0.1 M NaOH was investigated by in situ Fourier transform infrared reflection-absorption spectroscopy in the potential range, −0.76 to +0.46 V vs. Hg/HgO, OH−. The surface adsorbates were found to involve linear CO and bridged CO. The linear CO persisted on platinum in the entire potential range with gradual shifts to higher frequencies, ca. 70 cm−1/V while the bridged CO disappeared as the electrode potential reached −0.05 V. The oxidation products were car☐ylic acid and CO2. A potential excursion up to +0.46 V was found to cause a pH swing of more than 8 in the spectroelectrochemical thin layer due to the great extent of glucose oxidation. This was evident from the gluconic acid and CO2 peaks in the IR spectra.

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Electrochemical oxidation of α-D( + )-glucose on a polycrystalline platinum electrode in 0.1 M HC1O4 was studied in situ by Fourier transform infrared reflection-absorption spectroscopy. The spectra showed unambiguously that the major adsorbate on the platinum surface during the glucose oxidation over the potential range −0.20 to +0.40 V vs. a saturated calomel reference electrode is linearly adsorbed CO. The strong adsorption of this species inhibits the electrode reaction. The oxidation products in the solution were found to be gluconolactone, carboxylic acids and CO2 whose formation occurred to the greatest extent in the platinum oxide region.

Measurements have been performed to check on the Fleischmann-Pons (F-P) phenomena. They involved 1) measurements of tritium in the cell solution and the gas above it; and 2) determination of the D/Pd ratio by coulometry. Enhancement of tritium in the D2O solution was found in these two open glass cells, as well as in another four cells with Ni-anodes. The largest enhancement factor found was ~50. The neutron measurements were inconclusive.

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.

The addition of 0.5 weight percent (w/o) of the perfluorosulfonimide (PFSI), , as an additive to 85% in hydrogen‐oxygen fuel cell results in a 70 mV increase in the potential of the oxygen cathode (high surface area, 10% Pt on Vulcan XC‐72) at current densities up to 500 mA cm−2 at 70°C. This improvement is proposed to be due to the enhanced oxygen reduction kinetics caused by a physically adsorbed layer of the PFSI on the catalyst with the fluorocarbon tail toward the surface. The adsorbed layer creates a "dry cave" environment adjacent to the electrode surface which favors the competitive adsorption of oxygen on the catalyst surface. This adsorbed layer apparently does not interfere with water or proton transfer from or to the interface. Flooding of the gas structure of the porous cathode has not been observed at 0.5 w/o of the PFSI but has been observed at higher concentrations.

Oxygen reduction to superoxide was examined in acetonitrile on the basal planes of ordinary and highly oriented pyrolytic graphite (OPG, HOPG). The reaction has a lower apparent cathodic transfer coefficient on HOPG than OPG, probably due to part of the potential drop across the electrode—electrolyte interface occurring in a space charge region in the HOPG. Oxygen reduction to peroxide was examined in aqueous alkaline solution on HOPG with adsorbed 9,10-phenanthrenequinone and on OPG with chemically attached 2-aminoanthraquinone. On the adsorbed quinone surface, the kinetics of the initial electron transfer (to the quinone) are fast while the reaction of reduced quinone with solution-phase O 2 is the rate determining step. On the chemically attached quinone surface, the initial electron transfer is the rds because the quinone is further from the surface and in an unfavourable configuration for electron tunneling.

The catjpdoc polarization characteristics indicate that the presence of a pre-adsorbed surface layer of CoTSPc innibits the reduction of O2 to O2- on an ordinary pyroiytic graphite electrode (OPG) in AN and DMF solution of 0. 1 mol/L, TEAP, The transfer coefficient a and the heterogeneous rate constant k for this reaction or, OPG with and without pre-adsorbed CoTSPc obtained by rotating disk electrode method were found to be fairly close to thar obtained by cyclic voltammetry. The a remains almost the same, bat the k de creases by a factor of 2-5 with CoTSPc as compared with OPG alone. The possible reason is that the adsorbed CoTSPc as an anion renders the effective potential diffaence less negative, which thus lowers the rase of O2 reduction.

Polyacrylonitrile (PAN), mixed with Co(II) or Fe(II) salts and high-area carbon and then heat treated, has been found to yield very promising catalysts for O2 reduction in concentrated alkaline and acid solutions. The catalytic activities are comparable to those for the heat-treated corresponding transition metal macrocycles and polypyrrole black-based catalysts. The addition of the transition metal to the nitrogen-containing polymer, either before or after the heat treatment with carbon, is an important factor for good activity. The nitrile nitrogen of the PAN is probably retained and converted to pyridyl nitrogen during the heat treatment, and this nitrogen is believed to provide binding sites for the transition metal ions, which then act as catalytic sites for oxygen reduction to peroxide and its decomposition.