Photosystem II Acts as a Spin-Controlled Electron Gate during Oxygen Formation and Evolution

Abstract

The oxygen evolution complex (OEC) of photosystem II (PSII) is intrinsically more active than any synthetic alternative for the oxygen evolution reaction (OER). A crucial question to solve for the progress of artificial photosynthesis is to understand the influential interactions during water oxidation in PSII. We study the principles of interatomic electron transfer steps in OER, with emphasis on exchange interactions, revealing the influence of delocalizing ferromagnetic spin potentials during the catalytic process. The OEC is found to be an exchange coupled mixed-valence electron-spin acceptor where its orbital physics determine the unique activity of PSII. The two unpaired electrons needed in the triplet O molecule interact with the high spin state of the catalyst via exchange interactions; the optimal ferromagnetic catalyst and the resulting radical intermediates are spin paired. As a result, the active center of the CaMnO cofactor, stimulated by the driving potential provided by photons, works as a spin valve to accelerate the formation and release of O from diamagnetic HO.

Manipulating spin polarization of titanium dioxide for efficient photocatalysis

“…When the single electrons in different •OH species are in different spin directions, the hydroxyl radical will combine easily to generate H 2 O 2 17,22 , which will reduce the effective proportion of •OHs to take part in the surface oxidation reaction. On the contrary, •OHs with single electrons in the same spin direction are not easy to combine 17,23,46 , thus promoting the surface reactions of water splitting and degradation (especially for the case of TiO 2 -10).…”

On the Role of Ferromagnetic Interactions in Highly Active Mo‐Based Catalysts for Ammonia Synthesis

“…In this regard, one of the fingerprints in spintro‐catalysis is the general reduction of the free activation energies by a quantity that is proportional to the FM spin‐moment of the active sites. Within this correlation, we have used the Heisenberg Hamiltonian to quantify the QEI; that is: H QEI =▵J QEI ⋅ S cat where, ▵J QEI is a catalytic exchange coupling constant and S cat is the average spin moment at the active sites …”

“…Within this correlation, we have used the Heisenberg Hamiltonian to quantify the QEI; that is: H QEI =~J QEI ·S cat where,~J QEI is a catalytic exchange coupling constant and S cat is the average spin moment at the active sites. [31] We start the analysis from nitrogen defective unit cells, as the active catalysts present nitrogen vacancies at reaction conditions. [25] For that, we subtracted one of the sixteen nitrogen atoms in the unit cell of Fe 3 Mo 3 N, Co 3 Mo 3 N and FeCo 2 Mo 3 N, [32] as well as in an equivalent (with respect to the number of nitrogen atoms) Ni 2 Mo 3 N supercell (2 2 1); [33] thus making stoichiometries of the form M x Mo 3 N 0.94 .…”

Ferromagnetic ligand holes in cobalt perovskite electrocatalysts as an essential factor for high activity towards oxygen evolution

“…21,22 Nature has evolved excellent magnetic catalysts from abundant 3d-metals, e.g. during photosynthesis 23 , via engineering QSEI.…”