Solar-driven water-splitting provides a solution to the energy problem underpinning climate change

Abstract

The emergence of the oxygen-evolving photosystem two complex over 2.6 billion years ago represented the ‘big bang of evolution’ on planet Earth. It allowed phototrophic organisms to use sun light as an energy source to extract electrons and protons from water, and concomitantly release oxygen. Oxygenic photosynthesis not only created an aerobic atmosphere but also removed CO2 to produce the organic molecules that make up the current global biomass and fossil fuel. In addition, it paved the way for animal life. Today extensive burning of fossil fuels is reversing the results of photosynthesis through billions of years, rapidly releasing CO2 back into the atmosphere and consequently increasing the temperature of the planet. There is an urgent need to develop new sustainable energy sources, but the choice is not obvious. My approach to this problem has been to unravel the blueprint of photosystem II (PSII) and to develop an ‘Artificial Leaf’ technology. A significant step with respect to that mission was achieved at Imperial College when we could conclude from X-ray diffraction of PSII crystals, that the water-splitting catalytic centre consists of a unique Mn3Ca2+O4 cubane structure with a fourth dangler Mn oxo-bonded to the cubane. Here I use this and more recent structures to discuss the mechanism of water splitting and O–O bond formation. Furthermore, I will address how this information can be used to design novel water-splitting catalysts and highlight recent progress in this direction. My conviction is ‘if plants can do it, we can do it — after all it is all about chemistry’.