Comparison of cobalt and manganese in the chemistry of water oxidation

Recently, Nocera and coworkers claim that an “artificial leaf” – able to harvest up to 4.7% of incident photonic energy to split water and produce fuels using only Earth abundant elements – has been produced with much of its design inspired by photosynthetic elements [1]. In this short review, we compare the structure and function of the cobalt-based water oxidation center of the artificial leaf with what is known about the manganese-based oxygen-evolving complex (OEC) of photosystem II (PSII). The geometric structure, proposed oxidation state topology, and putative mechanism of water oxidation for the respective catalytic sites are discussed.

► The base unit of the Co-OEC structural motif mimics the OEC in PSII.
► Spectroscopic findings evince that the resting state is of a Co(III)/Co(IV) nature.
► Interlayer buffers facilitate water splitting through a charge balance mechanism.