Proton reduction in the presence of oxygen by iron porphyrin enabled with 2^nd sphere redox active ferrocenes

Hydrogen evolution in the presence of atmospheric level of oxygen is a significant barrier in the quest for an alternative, sustainable and green source of energy to counter the depleting fossil fuel sources and increasing global warming due to fossil fuel burning. Oxygen reduction is thermodynamically more favourable than proton reduction and it often produces reactive oxygenated species upon partial reduction which deactivates the catalyst. Thus, catalyst development is required for efficient proton reduction in the presence of oxygen. Here, we demonstrate an iron porphyrin having triazole containing 2^nd sphere hydrogen bonding residues appended with redox active ferrocene moieties (α₄-Tetra-2-(3-ferrocenyl-1,2,3-triazolyl)phenylporphyrin (FeFc₄)) as a bifunctional catalyst for fast and selective oxygen reduction to water and thus, preventing the proton reduction by the same catalyst from oxidative stress. Fe(0) is the active species for proton reduction in these iron porphyrin class of complexes and it is observed that the kinetics of proton reduction at Fe(0) state occurs at much faster rate than O₂ reduction and thus, paving the way for selective proton reduction in the presence of oxygen.