A study of Na(x)Pt3O4 as an O2 electrode bifunctional electrocatalyst

The present study suggests that polytetrafluoroethylene (PTFE) bonded Na(X)Pt3O4 gas porous diffusion electrodes may be a viable candidate for bifunctional O2 reduction and evolution activity. The electrodes exhibited Tafel slopes of about 0.06 V/decade for both O2 reduction an evolution. For O2 reduction, the 0.06 slope doubled to 0.12 V/decade at larger current densities. Preliminary stability testing at 24 C suggest that the Na(x)Pt3O4 electrodes were relatively stable at reducing and oxidizing potentials typically encountered at the O2 electrodes in a regenerative fuel cell

O2 reduction at the IFC orbiter fuel cell O2 electrode

O2 reduction Tafel data were obtained for the IFC Orbiter fuel cell O2 electrode (Au-10 percent Pt catalyst) at temperatures between 24 and 81 C. BET measurements gave an electrode surface area of about 2040 sq cm per sq cm of geometric area. The Tafel data could be fitted to three straight line regions. For current densities less than 0.001 A/sq cm, the slope was essentially independent of temperature with a value of about 0.032 V/decade. Above 0.001 A/sq cm, the two regions, designated in the present study as the 0.04 and 0.12 V/decate regions, were temperature dependent. The apparent energies of activation for these two regions were about 9.3 and 6.5 kcal/mol, respectively. Tafel data (1 atmosphere O2) were extrapolated to 120 C for predicting changes in overpotential with increasing temperature. A mechanism is presented for O2 reduction

Oxygen electrode bifunctional electrocatalyst NiCo2O4 spinel

A significant increase in energy density may be possible if a two-unit alkaline regenerative H2-O2 fuel cell is replaced with a single-unit system that uses passive means for H2O transfer and thermal control. For this single-unit system, new electrocatalysts for the O2 electrode will be required which are not only bifunctionally active but also chemically and electrochemically stable between the voltage range of about 0.7 and 1.5 V. NiCo2O4 spinel is reported to have certain characteristics that make it useful for a study of electrode fabrication techniques. High surface area NiCo2O4 powder was fabricated into unsupported, bifunctional, PTFE-bonded, porous gas fuel cell electrodes by commercial sources using varying PTFE contents and sintering temperatures. The object of this study is to measure the bifunctional activities of these electrodes and to observe what performance differences might result from different commercial electrode fabricators. O2 evolution and O2 reduction data were obtained at 80 C (31 percent KOH). An irreversible reaction (i.e., aging) occurred during O2 evolution at potentials greater than about 1.5 V. Anodic Tafel slopes of 0.06 and 0.12 V/decade were obtained for the aged electrodes. Within the range of 15 to 25 percent, the PTFE content was not a critical parameter for optimizing the electrode for O2 evolution activity. Sintering temperatures between 300 and 340 C may be adequate but heating at 275 C may not be sufficient to properly sinter the PTFE-NiCo2O4 mixture. Electrode disintegration was observed during O2 reduction. Transport of O2 to the NiCo2O4 surface became prohibitive at greater than about -0.02 A/sq cm. Cathodic Tafel slopes of -0.6 and -0.12 V/decade were assumed for the O2 reduction process. A PTFE content of 25 percent (or greater) appears to be preferable for sintering the PTFE-NiCo2O4 mixture

Corrosion testing of candidates for the alkaline fuel cell cathode

It is desirable to employ a corrosion screening test for catalyst or support candidates for the fuel cell cathode before entering upon optimization of the candidate or of the catalytic electrode. To this end, corrosion test electrodes, intended for complete immersion and maximum wetting, have been made with 30 to 40 vol. pct Teflon; with perovskites this is about 10 to 15 pct. The candidates were synthesized by methods intended for single-phase product without special emphasis on high surface area, although the substances tested were no coarser than 2 m squared/g. A typical loading was 25 mg/cm sq of the pure substance, usually on gold screen, a few mm squared of which were left bare for contacting. Contact to the gold lead wire was made by welding with a micro-torch or a spot-welder. Corrosion testing consisted of obtaining current-voltage data under flowing inert gas in the potential region for reduction of O2. The electrode was immersed in 30 pct KOH. Observations were made at 20 C and 80 C, and the results compared with data from gold standards. Results with some perovskites, pyrochlores, spinels, and interstitial compounds will be discussed

Corrosion testing of candidates for the alkaline fuel cell cathode

Current/voltage data was obtained for specially made corrosion electrodes of some oxides and of gold materials for the purpose of developing a screening test of catalysts and supports for use at the cathode of the alkaline fuel cell. The data consists of measurements of current at fixed potentials and cyclic voltammograms. These data will have to be correlated with longtime performance data in order to fully evaluate this approach to corrosion screening. Corrosion test screening of candidates for the oxygen reduction electrode of the alkaline fuel cell was applied to two substances, the pyrochlore Pb2Ru2O6.5 and the spinel NiCo2O4. The substrate gold screen and a sample of the IFC Orbiter Pt-Au performance electrode were included as blanks. The pyrochlore data indicate relative stability, although nothing yet can be said about long term stability. The spinel was plainly unstable. For this type of testing to be validated, comparisons will have to be made with long term performance tests

The effects of salinity and temperature on growth and survival of Australian snapper, Pagrus auratus larvae

The effects of salinity and temperature on performance were determined for Australian snapper, Pagrus auratus first-feeding to pre-metamorphosis larvae held in 100-l recirculation tanks. In the first experiment, performance was assessed after transfer from 35‰ at eight salinity treatments (5‰, 10‰, 15‰, 20‰, 25‰ 30‰, 35‰ and 45‰) in larvae from 3 to 21 days after hatching (dah). Survival of larvae was best within the range of 20–35‰. Final size of larvae was similar within the range of 10–35‰ (6.8 ± 0.1 to 7.1 ± 0.2 mm total length [TL]; 3.0 ± 0.3 to 3.3 ± 0.3 mg wet weight) but larvae were 15% shorter at 45‰. Final swimbladder inflation and feeding onset of larvae was not affected by salinity in the range of 10–45‰. The presence of calculi in the urinary bladder of larvae was correlated positively with increasing salinity but no relationship between urinary calculi and larval survival was observed. In a second experiment, performance was assessed after transfer from 21 °C at seven temperature treatments (15, 18, 21, 24, 27, 30 and 33 °C) in larvae from 3–21 dah. All larvae transferred from 21 °C to 30 °C and 33 °C died after 3 days and from 21 °C to 27 °C died after 9 days. Survival was not significantly different between 15 °C and 24 °C. Larval growth increased as temperature was increased; larvae at 24 °C (4.8 ± 0.2 mg wet weight) were 6-fold heavier than larvae at 15 °C. Swimbladder inflation of larvae grown at 18 °C, 21 °C and 24 °C was high (65.2 ± 18.0% to 86.7 ± 8.8%) and similar but inflation was lower in 15 °C and 27 °C. The incidence of urinary calculi occurred earlier and in a greater number of larvae when temperature was increased. Feeding onset was not affected by temperature. In a third experiment, performance was assessed at combinations of two salinities (20‰ and 35‰) and three temperatures (18 °C, 21 °C, and 24 °C) in larvae from 3 to 24 dah. Survival of snapper larvae was not significantly different between these treatments. Growth was not affected by salinity but larvae increased in size as temperature was increased and there was no interaction of salinity and temperature. The percentage of larvae that commenced feeding and inflated their swimbladders was similar in all treatments. Salinity and temperature influenced the incidence of urinary calculi and there was an interaction between the parameters. Based on our results in terms of larval performance (growth), development and survival, we conclude that the optimal conditions for larval rearing of snapper from first-feeding (3 dah) to pre-metamorphosis (24 dah) are combinations of salinity from 20‰ to 35‰ and a temperature of 24 °C