Reversibility and Growth Behavior of Surface Oxide Films at Ruthenium Electrodes

Abstract

Experiments are described in Which the nature of surface oxidation processes at Ru electrodes are investigated and compared with those of other noble metals. Surface oxidation of Ru is much more irreversible than at Pt, Au, or Rh and the oxide formed in sweeps taken to 1.4V can only be reduced in the H region, usually with some coevolution of Hf. However, surface oxidation already begins at potentials in, or close to, the H region; this behavior is somewhat similar to that of Pt in alkaline solutions. Upon repeated cycling into the oxide region up to 1.4V EH, a new state of t'he oxidized Ru surface is generated which exhibits remarkable reversibility of the i-V profile in anodic and cathodic sweeps taken to any potential in the range 1.4V. This effect is associated with a reversible redox process in the oxide film, probably between Ru(IV) and Ru (III), but reduction back to the metallic surface does not occur as it does in the initial sweeps. The behavior is somewhat similar to that previously observed with Ir. Time-dependent growth of the oxide film at Ru is observed, as at Other noble metals, and the direct logarithmic law applies. Similarities to the surface oxidation behavior of other noble metals, especially iridium, are pointed out and depend on anion adsorption.Ruthenium is of current interest as an electrocatalyst material, especially in combination with an oxidized Ti substrate, as an anode material for C12 evolution (1-3). From an electrochemical point of View, this metal has, however, been less well characterized than most other hoble-metaI materials, especially with regard to the state of adsorbed H at its surface near the reversible H2/H + potential and the nature of surface oxidation processes that occur at more positive potentials. In the case of Pt, Rh, Ir, and Au, the general surface oxidation characteristics were studied in some detail by Brei~er et al. in a number of papers (4-6) using the potentiodynamic sweep method of Will and Knorr (7), and by Vetter and Berndt (8), and Schultze and Vetter (9), using galvanostatic conditions. Apart from ~he literature quoted in an earlier preliminary communication on Ru (10), relatively little work has been Carried out on the surface oxidation behavior of Ru. An extended abstract (11) of a paper presented at the same meeting as that at which the present paper was given, reports comparisons between the properties and electrochemical behavior of oxide films on Ru and Ir and confirms the main features of the results given in our preliminary communication (10) in 1975.In the previous short communication (10) we showed (i) that a region of H deposition and re-ionization could be distinguished at Ru electrodes, (ii) that a region of surface oxidation occurred over a broad potential range, and (iii) that the processes of formation and reduction of surface oxide showed much more hysteresis than at Ir (12), Pt (13), Rh (13), or Au (14), depending on the positive potential limit in the anodic sweep (13) in cyclic voltammetry experiments.It is the purpose of this pape...

Clarifying the role of Ru in methanol oxidation at Rucore@Ptshellnanoparticles

“…7b) in 1 M CH 3 OH + 0.5 M H 2 SO 4 . 7a and b show that the Ru 48 @Pt 52 (1.1, EG) NPs have a lower catalytic activity than either the Ru 38 @Pt 62 (1.45,EG) or the Ru 38 @Pt 62 (1.9, EG) NPs, at both lower and higher potentials. Therefore, if the catalytic activity had been normalized to the total mass of metal in the NPs, it should have shown a similar trend to what was obtained here when the activities were normalized to the Pt area.…”

Epitaxial Growth of Ruthenium Dioxides on Ru(0001) Surface

“…The LEED electrons with wave vector k o impacts perpendicularly to the sample surface, the elastically diffracted electrons with wave vector k are accelerated by the grid potential of +3.8 keV and crush the fluorescent screen lighting up the reflection spots. On the other hand, the RHEED experiment was performed with an electron beam energy of 40 keV (with a wave vector k o ) at grazing incidence of 2-3 o and the elastically diffracted electrons give Ru(0001) surface was oxidized to RuO 2 by exposure to large amounts of molecular oxygen at elevated sample temperatures (600-800 K) under UHV conditions, growing epitaxially with (110) face on Ru(0001) [16], while single crystals of (100) RuO 2 are grown in a multizone furnace using a vapor transport method under oxygen flow [12]. On the other hand, the ruthenium oxide films were electrodeposited on tin doped indium oxide (TIO) substrate from an aqueous solution, for which the monocrystalline phase was characterized by XRD measurements [17], while the hydrous RuO 2 .…”

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