Fundamental Aspects on the Catalytic Activity of Metallomacrocyclics for the Electrochemical Reduction of O₂

Molecular oxygen is certainly the most abundant oxidant on earth. Practically all of it is generated by living organisms, and without life it would not be present in the atmosphere. Molecular oxygen is generated by photosynthesis on earth and in the sea, so it can be considered a by-product of some living organisms and other living organisms profit from the free energy available from this molecule to sustain aerobic life. So molecular oxygen is a thermodynamically unstable molecule and will decay via reduction to form more stable species. So the reduction of molecular oxygen is favorable on thermodynamic grounds. However, at room temperature it reacts very slowly with reductants in the absence of catalysts. Indeed this is good, otherwise many things will burn rapidly at room temperature and life would not be possible as we know it.