Catalytic solar water splitting inspired by photosynthesis. homogeneous catalysts with a Mechanical ("Machine-like") action

Chemical reactions may be controlled by either: the minimum threshold energy that must be overcome during collisions between reactant molecules / atoms (the Activation Energy, Ea), or: the rate at which reactant collisions occur (the Collision Frequency, A) (for reactions with low Ea). Reactions of type (2) are governed by the physical, mechanical interaction of the reactants. Such mechanical processes are unusual, but not unknown in molecular catalysts. We examine the catalytic action and macroscopic properties of several abiological mechanical catalysts and show that they display distinct similarities to enzymes in general. An abiological model of the Photosystem II Water Oxidizing Complex that appears to employ a mechanical action has now been found to be a remarkably active and sustained molecular catalyst of water oxidation when illuminated by sunlight. A free-standing Dye-Sensitized Solar Cell that spontaneously splits water into hydrogen and oxygen has been developed using this catalyst.