Ruthenium oxide oxygen evolution reaction

Fig. 14. Rotating (45 Hz) ruthenium dioxide/titanium dioxide electrode (35% w/w ruthenium dioxide) in 0.1 M NaCl solution, (a) Standard rate constant-potential curve for the chloride oxidation reaction [reaction (1)] assuming a constant Tafel slope of 70mV, Da — 5 x 10 6cm s 1, Z)cl2 = 7 x 10 6cm s 1, E[ = 1050mV SCE, and R = 2.2ohm cm2. The characteristics of the oxygen evolution reaction [reaction (2)] with a Tafel slope of 200 mV were chosen to be fej, = 1 x 10 8 cm s, EH = 1257 mV SCE and Dq2 = 1 x 10 5 cm2 s 1, (b) Common experimental and calculated current-potential curve using parameters of Fig. 14(a). The broken curve refers to the calculated "reversible curve.

Direct electrooxidation is theoretically possible at low potentials, before oxygen evolution, but the reaction rate usually has low kinetics that depends on the electro-catalytic activity of the anode. High electrochemical rates have been observed using noble metals such as Pt and Pd, and metal-oxide anodes such as iridium dioxide, ruthenium-titanium dioxide, and iridium-titanium dioxide (Foti et al. 1997). 

Dimensionally Stable Anodes— These anodes are composed of a base metal such as titanium, coated with a precious metal oxide (e.g., ruthenium dioxide). Such anodes can be used instead of Pt or carbon for oxygen evolution counter electrodes in an organic electrosynthesis. They have also found some applications for organic oxidation reactions [61]. 

One of the first metal oxides to be examined electrochemically on a diamond substrate was ruthenium dioxide [115, 116]. This material is important both for electrochemical capacitor and electrocatalytic applications (chlorine evolution). Another example is cobalt hydrous oxide, which has catalytic activity for oxygen evolution [117]. A very recent example is lead dioxide [118]. A metal oxide (V2O3) has also been supported on particulate diamond as a catalyst for an organic gas-phase reaction [119]. 

Transition metal surfaces enriched with S, Se and Te, have been considered as candidates for DAFC cathode catalysts [112-115], For example, ruthenium selenium (RuSe) is a weU-studied electro-catalyst for the ORR [116, 117]. The ORR catalysis on pure Ru surfaces depends on the formation of a Ru oxide-like phase [118]. Ru is also an active catalyst for methanol oxidation. On the other hand, the activity of the ORR on RuSe is found not be affected by methanol [116]. RuS, has also been reported insensitive to methanol [119-122], DPT studies of model transition metal surfaces have provided with atomistic insights into different classes of reactions relevant to fuel cells operation, such as the hydrogen evolution [123], the oxygen reduction [124], and the methanol oxidation [125] reaction. Tritsaris, et al. [126] recently used DPT calculatimis to study the ORR and methanol activation on selenium and sulfur-containing transition metal surfaces of Ru, Rh, Ir, Pd, Co and W (Fig. 8.9). With RuSe as a starting point, the authors studied the effect of the Se on... 

---