A Z-Scheme-Inspired Photobioelectrochemical H O/O Cell with a 1 V Open-Circuit Voltage Combining Photosystem II and PbS Quantum Dots.

A biohybrid photobioanode mimicking the Z-scheme has been developed by functional integration of photosystem II (PSII) and PbS quantum dots (QDs) within an inverse opal TiO architecture giving rise to a rather negative water oxidation potential of about -0.55 V vs. Ag/AgCl, 1 m KCl at neutral pH.

Structures of the intermediates of Kok's photosynthetic water oxidation clock.

Inspired by the period-four oscillation in flash-induced oxygen evolution of photosystem II discovered by Joliot in 1969, Kok performed additional experiments and proposed a five-state kinetic model for photosynthetic oxygen evolution, known as Kok's S-state clock or cycle. The model comprises four (meta)stable intermediates (S, S, S and S) and one transient S state, which precedes dioxygen formation occurring in a concerted reaction from two water-derived oxygens bound at an oxo-bridged tetra manganese calcium (MnCaO) cluster in the oxygen-evolving complex. This reaction is coupled to the two-step reduction and protonation of the mobile plastoquinone Q at the acceptor side of PSII.