O2 reduction reaction

Before considering these catalysts, some background on the O2 reduction reaction will be reviewed ( ). 

RECENT DEVELOPMENTS IN TTIE ELECTROCATALYSIS OF THE O2 REDUCTION REACTION... 

TABLE 9.4 A Comparison of Surface Area and the Catalytic Activity Data for Pt/C and Au/Pt/C Before and After 30,000 Potential Cycles from 0.6 to 1.1 V under the Oxidizing Conditions of the O2 Reduction Reaction. Reprinted with Permission from Zhang et al. [2007b]... 

The O2 reduction reaction affects not only the steady-state deposition kinetics, but also the initiation of deposition, the so-called induction time [126, 127], At the beginning of the deposition process, the open circuit potential (Eoc) of either a uniformly catalytically active substrate, or a catalyst particle on an insulator, will be higher than that required for electroless deposition to occur. This is a consequence of the surface of the catalyst being covered with O or OH species which mask the catalytic activity of the surface the value of would be expected to be in the range of... 

V to +0.7 V vs. RHE for a Pd surface. Normally, this is anodic, or positive, with respect to the Em value of the electroless reaction (Fig. 1). Following removal of the oxide species from the catalyst surface, whether deposition subsequently initiates or not depends on the interplay between the kinetics of the parallel metal ion and O2 reduction reactions, and oxidation of the reducing agent. Once an appropriate Em value is reached, metal deposition will occur. 

The lower the slope, the lower the activation loss for the O2 reduction reaction in acid media, the observed slope is 0.060 V/ decade and it can be obtained theoretically by assuming the oxygen discharge step as the slowest one (the rate determining step, the r.d.s. ( 7)). For hydrogen the mechanism is different and the r.d.s. is the atomic dissociation and in this case a Tafel slope of 0.030... 

Pt is, of course, not a good electrocatalyst for the O2 evolution reaction, although it is the best for the O2 reduction reaction. However, also with especially active oxides of extended surface area, the theoretical value of E° has never been observed. For this reason, the search for new or optimized materials is a scientific challenge but also an industrial need. A theoretical approach to O2 electrocatalysis can only be more empirical than in the case of hydrogen in view of the complexity of the mechanisms. However, a chemical concept that can be derived from scrutiny of the mechanisms mentioned above is that oxygen evolution on an oxide can be schematized as follows [59] ... 

This article concentrates on principles and methodologies for examination and interpretation of experiments and behavior of some selected electrocatalytic reactions, rather than providing an exhaustive catalog of the very many works that have been published in this fleld. Such a review would take much more space than is allocated for this article. Several other relevant reviews are to be noted, as follows, in the references indicated Sakellaropoulos (4), Trasatti and Lodi (5), Conway (6), Conway and Angerstein-Kozlowska (7), Yeager (S) and others on the O2 reduction reaction, Jaksic (9), O Sullivan... 

Parthasarathy A., Martin C. R. and Srinivasan S. (1991) Investigations of the O2 reduction reaction at the platinum Nahon interface using a solid-state electrochemical cell. J. Electrochem. Soc. 138, 916-921. 

As mentioned above, the O2 reduction reaction via 4 electrons must involve the breaking of the 0-0 bond (whether in O2, H02, or H2O2) and the formation of an O-H bond. So, a more reactive surface, such as one characterized by a... 

Lima F, Zhang J, Shao M, Sasaki K, Vukmirovic M, Ticianelli E, Adzic R (2007) Catalytic activity-d-band center correlation for the O2 reduction reaction on platinum in alkaline solutions. J Phys Chem C 111 404-410... 

According to this equation, we can discuss two cases one is the case when the reductant in Reaction (2-II) is insoluble (such as the metal ions deposition) or solvent (such as O2 reduction reaction in aqueous solution to produce water), and the other case is both oxidant and reductant are soluble. 

Figure 4.10 Current-potential curves for O2 reduction reaction at a bare glassy carbon (GC) RDE in 02-saturated 0.5 M H2SO4. GC surface oxidation time 0 min (dashed line) 1 min (thin line) 5 min (thick line) 20 min (very thick line). Scan rate, 10 mV s electrode rotation speed, 2000 rpm. Reprinted from Ref. 31, with permission from Elsevier.

Figure 4.11 (A) Dimetal complex (Co2TAPH) (N03)4. (TAPH = 6,7,8,9,12,19, 20,21,22,25-decahydro-8,8,10,21,21,23,-hexamethyl-5,26 13,18-/)/s(azo)-dibez(1,2,6,7,12,13,17,18)oxaazacyclodocosine) (B) Face-to-face Co—Co 4-porphyrin. (Reprinted from Ref 17, with permission from Elsevier.) (C) Cis and trans Co-O-O-Co facial configuration and (D) Co-corrole compounds for O2 reduction reaction. ...

---