The oxygen reduction/evolution reaction
Published Online: 15 DEC 2010
Copyright © John Wiley & Sons, Ltd. All rights reserved.
Handbook of Fuel Cells
How to Cite
Zagal, J. H. 2010. Macrocycles. Handbook of Fuel Cells. .
- Published Online: 15 DEC 2010
The catalysis of the reduction of oxygen on supported metal macrocyclics is discussed in terms of electronic interactions of the dioxygen molecules with metal centers that lead to the weakening of the OO bond and to a lowering of activation energy. Correlations between electronic properties of the macrocyclic complexes and activity are also discussed, such as the influence of the redox potential of the metal center in the electrocatalysis. The overall 2- versus 4-electron reduction mechanisms on metallo-macrocyclics are discussed including the different approaches used in the literature to achieve 4-electron reduction mechanisms by designing face-to-face binuclear complexes, polymerized metal complexes or macrocycles substituted with peripheral redox groups. The systems that are more promising for practical applications, such as the heat-treated carbon supported catalysts, are discussed in detail and with explanations on how these pyrolyzed catalysts have higher activity and better stability compared with other supported macrocyclic systems. The requirement for the existence of the “burned-in” MN4 moiety also known as the “super-site” in heat-treated catalysts is emphasized. Heat-treated carbon supported macrocyclics catalysts are not poisoned by methanol and in principle they can be suitable for low-temperature acid electrolyte fuel cells. The methods of preparation of supported catalysts include: (a) modified electrodes by adsorption or surface modification; (b) heat-treated carbon supported catalysts; (c) influence of carbon surface modification and electrodes prepared by polymerized macrocyclics; and (d) methanol tolerance and comparison of the activities with platinum-based electrocatalysts.
- heat-treated macrocyclics;
- pyrolysis temperature;
- face-to-face porphyrins;
- methanol tolerance;
- redox catalysis;
- Schiff bases;
- N-4 chelates