Trapping an iron(VI) water-splitting intermediate in nonaqueous media

Abstract

Understanding the mechanisms of highly-active, earth-abundant water oxidn. electrocatalysts can guide the development of advanced water-splitting devices that convert renewable electricity to clean fuels. Unfortunately, catalytic intermediates are difficult to isolate and characterize because they tend to be extremely transient and present at low concns. A typical approach to this problem is to slow down turnover by limiting the availability of substrate. However, in cases where substrate and solvent are identical-such as in water oxidn.-the soln. can be more complex. By dramatically limiting the availability of substrate (water and hydroxide) in nickel-iron catalyzed heterogeneous water oxidn., we have obsd. and characterized a high-valent iron intermediate. Orthogonal spectroscopies indicate that the intermediate contains iron in the rare 6+ oxidn. state. This ferrate analog makes dioxygen upon addn. of hydroxide and can be stepwise regenerated by anodic polarization.