Oxygen evolution reaction electrocatalysis

At IREQ, besides the participation in the field tests run by the engineers of Hydro-Quebec (12), the main effort has been to tackle fundamental problems in the field of electrocatalysis (18-22) and of anodic oxidation of different potential fuels (23-26). A careful and extensive study of the electrochemical properties of the tungsten bronze has been carried out (18-20) the reported activity of these materials in acid media for the oxygen reduction could not be reproduced and this claim by other workers has been traced back to some platinum impurities in the electrodes. Some novel techniques in the area of electrode preparation are also under study (21,22) the metallic deposition of certain metals on oriented graphite show some interesting catalytic features for the oxygen reduction and also for the oxygen evolution reaction. 

In this chapter, the focus will be on trends in electrocatalysis of the water-splitting reaction or the oxygen evolution reaction (OER), which is the reaction at the anode side in an electrolysis cell. Furthermore, simple framework for addressing OER applying DFT simulations will be presented. For further reading, there are two previous book chapters where the approach has been reviewed [3, 4],... 

XVII. Electrocatalysis and Kinetic Behavior of Oxygen Evolution Reaction... 

S. Trasatti, Electrode kinetics and electrocatalysis of hydrogen and oxygen electrode reactions. 4. The oxygen evolution reaction, in Electrochemical Hydrogen Technologies (Ed. H. Wendt), Elsevier, Amsterdam, 1990, pp. 104-135. 

Until now, the methodology available to study charge transfer reactions at soft interfaces has been rather mature, and studies in the field have shifted to the study of catalyzed reactions such as the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), or even oxygen evolution reaction (OER). Eor this, two classes of catalysts have been used (i) molecular catalysts and (ii) nanoparticle solid catalysts. These two approaches draw their inspiration from classical molecular catalysis and from electrocatalysis, respectively. 

However, the electrochemical oxygen evolution reaction (OER) from the water in acid solutions is thermodynamically slightly more favorable than the CER given by Eq. 2 (the fP value for the OER is 1.229 V). Bearing in mind that electrocatalysis essentially implies the activity and selectivity of various electrode materials toward a certain electrode reaction [2], the correct choice of electrode material that is of high electrocatalytic activity for the CER and of lower activity for the OER is of extreme importance. Anyhow, CAT is always subjected to current loss due to the OER as a side reaction. This fact sets additional demands toward the anode material for the CER, i.e., its stability toward the OER and consequently its durability in CAT. 

Initial studies on electrocatalysis for fuel cell application using amorphous alloys were related to the oxygen evolution reaction (OER) [131,132], Ni-based amorphous alloys have a significant contribution to the development of materials for application in fuel cells due to their high stability in alkaline medium, relative low overpotential, low cost, and high corrosion resistance. The synthesis of the alloys is relatively simple. The catalyst can be obtained via the mechanical alloy technique, where the metallic elements are placed in a planetary ball mill for several hours, at the desired ratio. An important observation is that the as-synthesized catalyst does not display significant catalytic activity as compared to the crystalline material. An acid treatment with HE or HF-HNO3 is required for activation of the material surface [133,134],... 

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] ... 

The first step was the evolution away from the Schottky barrier model of photoelectrochemistry caused by the evidence from the late 1970s onward that the rate of photoelectrochemical reactions was heavily dependent on surface effects (Uosaki, 1981 Szklarczyk, 1983). This was followed by the use of both a photocathode and a photoanode in the same cell (Ohashi, 1977). Then the use of nonactive thin protective passive layers of oxides and sulfides allowed photoanodes to operate in potential regions in which they would otherwise have dissolved (Bockris and Uosaki, 1977). The final step was the introduction of electrocatalysis of both hydrogen and oxygen evolution by means of metal islets of appropriate catalytic power (Bockris and Szklarczyk, 1983). 

Feng, J., Johnson, D. C., Lowery, S. N. and Carey, J. (1994) Electrocatalysis of anodic oxygen-transfer reactions evolution of ozone. J. Electrochem. Soc. 141, 2708-2711. 

Research in electrocatalysis was strongly stimulated in the early 1960s by efforts toward the development of various types of fuel cells. Studies were initiated on the various factors influencing the rates not only of hydrogen evolution but also of other reactions, particularly cathodic oxygen reduction and the complete oxidation of simple organic substances ( fuels ) to carbon dioxide. The... 

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