Rhodium Electrodes Research Articles

The behaviour of formic acid on a rhodium electrode

Formic acid adsorption and its oxidation have been studied on a rhodium electrode using radiochemical and electrochemical methods. The dual path mechanism for the HCOOH oxidation on rhodium has been verified. It is supposed that the mixed ·COOH and :CO species, coupled by hydrogen bonding, form a combined product of the HCOOH chemisorption. It has been concluded that the rate determining step in the oxidation of strongly bound species should be considered as a charge transfer process. The adsorbed OH radicals as well as the water molecules are most likely the surface oxidant involved in the oxidation of the chemisorbed species. The data obtained for the adsorption and the oxidation of HCOOH on rhodium are often compared with those found for platinum.

The Fe(II)–Fe(III) and Hydroquinone‐Quinone Reactions on Oxygen‐Covered Rhodium Electrodes

The kinetics of the Fe(II)–Fe(III) and of the hydroquinone‐quinone reaction were investigated on smooth rhodium covered with oxygen to the extent of monolayer charge equivalents (2 electrons per oxygen atom). For the Fe(II)–Fe(III) system the apparent rate constant varies systematically from at to at and it does not seem to decrease significantly after that. The charge transfer coefficient is independent of θ. For the hydroquinone‐quinone system, at and at and it varies only little for . The charge transfer coefficient is . Data are interpreted on the basis of a blocking effect, the charge transfer rate on oxygen‐covered rhodium being negligible as compared to that on the free surface.

コバルトめっき電極の水素過電圧に及ぼすバナジウム，モリブデン共電着の影響

Hydrogen evolution overpotential of the cobalt plated cathode in a 3.0mol/dm3 NaOH solution at 80°C was studied by comparing polarization curves. For a 20A/dm2 plating current density with 3.0mol/dm3 urea added to the cobalt citrate plating bath, a low hydrogen overpotential value was obtained. The value was same to that of rhodium electrode. Vanadium or molybdenum co-deposited cobalt plating cathode had lower hydrogen overpotential than above mentioned pure cobalt plated cathode. Suitable plating conditions for low hydrogen overpotential cathodes were above 4×10-3 mol/dm3(about 0.8g/dm3) vanadium pentoxide or ammonium molybdate addition and above 30A/dm2 plating current densities. Value of overpotential at 25A/dm2 current density was 0.1V. This is a comparable value with that of platinized platinum cathode.

The potential dependence and kinetics of HCOOH adsorption on rhodium electrodes

The formic acid adsorption on an electrochemically prepared rhodium electrode has been studied by the radiochemical method. Electrochemical properties of the rhodium electrode surface in 0.5 M H 2 SO 4 have been investigated by cyclic voltammetry. It has been shown that starting from E =0.20 V the rate of HCOOH adsorption is markedly potential dependent being practically independent of the electrode potential up to E =0.20 V. It seems that the HCOOH adsorption process may be explained on the basis of the two-sites kinetics model. The data obtained for HCOOH adsorption on a rhodium electrode have been compared with those for a platinum electrode reported previously.

The potential dependence and kinetics of HCOOH adsorption on rhodium electrodes

The formic acid adsorption on an electrochemically prepared rhodium electrode has been studied by the radiochemical method. Electrochemical properties of the rhodium electrode surface in 0.5 M H 2SO 4 have been investigated by cyclic voltammetry. It has been shown that starting from E=0.20 V the rate of HCOOH adsorption is markedly potential dependent being practically independent of the electrode potential up to E=0.20 V. It seems that the HCOOH adsorption process may be explained on the basis of the two-sites kinetics model. The data obtained for HCOOH adsorption on a rhodium electrode have been compared with those for a platinum electrode reported previously.

Neuropathological effects of intracerebral platinum salt injections.

Multiple intracerebral injections of a mixture of platinum salts were made in 9 adult cats and the brains studied by light and electron microscopy at 5-12 days post injection. At the center of the lesions normal cortical architecture was completely replaced by edematous areas containing lipid-laden macrophages and cellular debris. The lesion periphery was characterized by perivascular edema and degenerative changes including cytoplasmic lipid inclusions and vacuolations with selective vulnerability of neurons. Membranous cytoplasmic bodies (MCB), zebra bodies and multiple nucleoli were observed in several cell types. This ultrastructural pattern, mimicked to some extent, that observed following electrical stimulation of brain following chronically implanted platinum and rhodium electrodes. The induction of zebra bodies and MCB, both of which are morphologic features of human neurolipidoses associated with congenital enzyme deficiencies, suggests an inhibitory effect of platinum on brain enzymes. Functional electrical stimulation of brain and other organs is currently being employed in a wide variety of clinical applications (14, 15). A mandatory consideration is that of the long-term effects of the stimuli as well as the electrodes themselves on the tissues involved. The histological effects and mechanisms of tissue damage following chronic application of electrical stimuli to brain have been the subject of several investigations in this laboratory (1, 14-18). Factors contributing to neural damage induced by electrical stimulation include noxious products resulting from electrode dissolution. In vitro studies employing electrochemical (3,9) and scanning electron microscopy (6) techniques have established that erosion of noble metal electrodes occurs, even when passing relatively small stimulation currents. Such electrode dissolution is of particular importance in long term applications of neural prostheses. The present study was initiated to assess the contribution of platinum electrode erosion products to neurla damage following electrical stimulation of brain, specifically to distinguish morphological changes resulting directly from electrode solubilization as opposed to electrical factors. Accordingly, intracerebral injections of graded volumes of platinum salts were made in an attempt to stimulate the presence of platinum electrode dissolution products.

Cortical Histopathology following Stimulation with Metallic and Carbon Electrodes; pp. 126–141

Stimulation of the cat striate cortex with polished 1 mm2 gold, platinum, rhodium or carbon electrodes for 40h, at 50 Hz, and 0.5 msec duration, results in tissue damage at current densities of 0.6 A/cm2. At 0.1 A/cm2 rhodium and carbon were toxic to brain. In vitro gold and platinum corroded after 1,500-2,300 h of testing in simulated cerebrospinal fluid. The materials utilized are not suitable for long-term chronic electrodes for neural prosthetics.

The oxygen evolution reaction on rhodium and iridium electrodes in 85% orthophosphoric acid

The oxygen evolution reaction on rhodium and iridium electrodes in 85% orthophosphoric acid

The oxygen evolution reaction on rhodium and iridium electrodes in 85% orthophosphoric acid

The oxygen evolution reaction on rhodium and iridium electrodes in 85% orthophosphoric acid

Hydrogen adsorption on platinum, iridium and rhodium electrodes at reduced temperatures and the determination of real surface area

Cyclic voltammograms of platinum and iridium electrodes in 5 M sulphuric acid at −72°C display much greater separation of the hydrogen adsorption and evolution currents than at 20°C. This enables the saturation hydrogen coverage and the real surface area of an electrode to be determined directly from the voltammogram. The adsorption of hydrogen on rhodium is not sufficiently rapid to maintain equilibrium on a voltammogram at reduced temperatures, and the saturation hydrogen coverage cannot be obtained directly. The accuracy of determination of surface area for the three metals from measurements at 20–25°C is discussed. The voltammograms for platinum electrodes at −72°C do not show the “third anodic hydrogen peak” observed at 20°C. The processes which have been suggested to account for this peak are discussed.

Hydrogen adsorption on platinum, iridium and rhodium electrodes at reduced temperatures and the determination of real surface area

Cyclic voltammograms of platinum and iridium electrodes in 5 M sulphuric acid at −72°C display much greater separation of the hydrogen adsorption and evolution currents than at 20°C. This enables the saturation hydrogen coverage and the real surface area of an electrode to be determined directly from the voltammogram. The adsorption of hydrogen on rhodium is not sufficiently rapid to maintain equilibrium on a voltammogram at reduced temperatures, and the saturation hydrogen coverage cannot be obtained directly. The accuracy of determination of surface area for the three metals from measurements at 20–25°C is discussed. The voltammograms for platinum electrodes at −72°C do not show the “third anodic hydrogen peak” observed at 20°C. The processes which have been suggested to account for this peak are discussed.

Electrosorption characteristics of thin layers of noble metals electrodeposited on different noble metal substrates

Thin electrodeposits of palladium on gold and rhodium on platinum display composite hydrogen and oxygen electrosorption properties. This behaviour is interpreted in terms of alloy formation brought about by interdiffusion of surface atoms. In contrast, platinum on gold, rhodium on gold and palladium on rhodium electrodes exhibit the electrosorption characteristics of the individual pure metals. This implies a lack of interdiffusion in these systems, consistent with the known immiscibility of the component metals. The relation between electrosorption properties and amount of metal deposited provides supporting evidence for the conclusion that the active surface in chemisorption is confined to a few atomic layers.

Electrosorption characteristics of thin layers of noble metals electrodeposited on different noble metal substrates

Summary Thin electrodeposits of palladium on gold and rhodium on platinum display composite hydrogen and oxygen electrosorption properties. This behaviour is interpreted in terms of alloy formation brought about by interdiffusion of surface atoms. In contrast, platinum on gold, rhodium on gold and palladium on rhodium electrodes exhibit the electrosorption characteristics of the individual pure metals. This implies a lack of interdiffusion in these systems, consistent with the known immiscibility of the component metals. The relation between electrosorption properties and amount of metal deposited provides supporting evidence for the conclusion that the active surface in chemisorption is confined to a few atomic layers.

A study of the dissolution of platinum, palladium, rhodium and gold electrodes in 1 M sulphuric acid by cyclic voltammetry

A study of the dissolution of platinum, palladium, rhodium and gold electrodes in 1 M sulphuric acid by cyclic voltammetry

Labour in the rabbit: effect of electrical stimulation applied to the infundibulum and median eminence.

SUMMARY Labour was induced by electrical stimulation of the infundibulum and median eminence in the conscious prepartum rabbit. The stimulus was applied for 20 s through a chronically implanted platinum—rhodium electrode and consisted of 1 mA biphasic pulses at 50/s. The first visible signs of labour occurred 1·5–3·0 min after stimulation and activity usually ceased within 25 min. This was sometimes sufficient for the delivery of the entire litter. The litters ranged from 5 to 11 pups. Frequently, labour ceased before all the young were expelled, but labour was easily restarted by a further period of stimulation. There were cases in which labour was restarted on more than four occasions before parturition reached completion. Parturition was sometimes left in a suspended state for more than 24 h. The viability of the pups was not adversely influenced by the protracted nature of such parturitions. Stimulation was most effective at inducing labour when applied close to the predicted time of parturition and the treatment was almost totally ineffective when applied more than 48 h before the predicted time. Nest-building was not precipitated by the premature birth of the young and sometimes occurred a day or more after parturition. The stimulation parameters used for the induction of labour caused large milk-ejection responses when applied to the same animals during lactation. Some of these milk-ejection responses were equal to the release of more than 100 mu. oxytocin. These results suggest that the rapid expulsion of the pups during natural labour in the rabbit could be the result of a sudden and very large release of oxytocin.

Adsorption and anodic oxidation of methanol on iridium and rhodium electrodes

Adsorption and electro-oxidation of methanol on smooth iridium and rhodium electrodes have been studied. The regularities obtained were compared with the results of previous measurements on smooth platinum. The adsorption of methanol on iridium has been established as characterized by regularities peculiar to a surface with an exponentially distributed inhomogenity of adsorption sites (Freundlich isotherm, linear change of the activation energy of adsorption with logarithm of surface coverage). The adsorption regularities for rhodium are more complex. The character of the isotherms on iridium and rhodium, as well as on platinum, does not depend on the nature of adsorbed neutral particles (methanol, hydrogen etc) and is apparently determined by the electrode surface properties. As follows from kinetic regularities (influence of potential, concentration and pH of solution, surface coverage) the rate-determining step of steady-state methanol electro-oxidation on iridium and rhodium is the oxidation of carbonaceous chemisorbed particles by adsorbed OH radicals.

The nature of adsorbed oxygen on rhodium, palladium and gold electrodes

The nature of adsorbed oxygen on rhodium, palladium and gold electrodes

Oxygen reduction studies at smooth pre-reduced ruthenium and rhodium electrodes in 85% orthophosphoric acid

Summary Cathodic reduction of oxygen has been studied on bright oxide-free rhodium and ruthenium electrodes in purified 85% orthophosphoric acid as a function of temperature. Tafel slopes on reproducibly clean rhodium electrodes are close to RT/F ; on ruthenium the corresponding value is about 2RT/F . The Tafel slope on ruthenium did not have the theoretical temperature-dependence. A similar effect was previously noted on gold and iridium electrodes under the same conditions 5 . On rhodium an apparent increase in Tafel slope occurs at higher current densities. This may indicate a change in mechanism. Ruthenium behaves like iridium 5 in the presence of impurities: These result in deactivated electrodes with lower Tafel slopes. The exchange current on rhodium was about 2 orders of magnitude less than that on platinum (slope also RT/F ) 6 under the same conditions. The value of i 0 on ruthenium was similar to that noted on iridium (about 10 −11 A cm −2 ) under the same conditions. Oxygen reduction is first-order on these metals. Activation energies at the reversible potential were determined to be 22.0±1.5 kcal on rhodium, similar to the value (22.9 kcal) reported on platinum 6 , and 11.7±0.5 kcal on ruthenium, somewhat less than the value (12.6 kcal) on iridium 5 . The suggested rate-determining step on these metals is O 2 + H + + e − → − O 2 H ads On rhodium, it occurs under Temkin adsorption conditions in the potential range where medium coverages of adsorbed O and OH radicals (from water oxidation) are present on the electrode. On ruthenium, high coverages of these radicals occur, and adsorption is Langmuirian.

Oxygen reduction studies at smooth pre-reduced ruthenium and rhodium electrodes in 85% orthophosphoric acid

Cathodic reduction of oxygen has been studied on bright oxide-free rhodium and ruthenium electrodes in purified 85% orthophosphoric acid as a function of temperature. Tafel slopes on reproducibly clean rhodium electrodes are close to RT/F; on ruthenium the corresponding value is about 2RT/F. The Tafel slope on ruthenium did not have the theoretical temperature-dependence. A similar effect was previously noted on gold and iridium electrodes under the same conditions5. On rhodium an apparent increase in Tafel slope occurs at higher current densities. This may indicate a change in mechanism. Ruthenium behaves like iridium5 in the presence of impurities: These result in deactivated electrodes with lower Tafel slopes. The exchange current on rhodium was about 2 orders of magnitude less than that on platinum (slope also RT/F)6 under the same conditions. The value of i0 on ruthenium was similar to that noted on iridium (about 10−11 A cm−2) under the same conditions. Oxygen reduction is first-order on these metals. Activation energies at the reversible potential were determined to be 22.0±1.5 kcal on rhodium, similar to the value (22.9 kcal) reported on platinum6, and 11.7±0.5 kcal on ruthenium, somewhat less than the value (12.6 kcal) on iridium5. The suggested rate-determining step on these metals is O2 + H+ + e− → − O2Hads On rhodium, it occurs under Temkin adsorption conditions in the potential range where medium coverages of adsorbed O and OH radicals (from water oxidation) are present on the electrode. On ruthenium, high coverages of these radicals occur, and adsorption is Langmuirian.

Oxygen overvoltage on bright rhodium

Oxygen overvoltage data were determined galvanostatically and potentiostatically for the anodic evolution and cathodic reduction of O2 on bright rhodium electrodes in O2-saturated 2 N H2SO4 solutions with and without added H2O2.The over-all electrode reaction on Rh, O2 electrodes is the O2/H2O reaction and the mechanism is the same as that favoured on Pt, O2 electrodes. Oxygen is adsorbed from solution on Rh as an electronically conducting monolayer of oxygen atoms; but with anodic polarization above 1400 mV, oxygen is dissolved in the surface layers of the metal producing a Rh-O alloy. The adsorbed layers of oxygen are more tightly bound to the Rh surface than to a Pt surface-giving rise to higher over-voltage values on Rh electrodes. Double-Iayer capacitance measurements support these conclusions. The rhodium surface is a poor catalyst for decomposition of H2O2. Of the noble metals, rhodium is one of the poorer materials that may be selected for the construction of an oxygen cathode.