ABSTRACT
There is a growing need to convert electrical energy from renewable sources to stored chemical energy in the form of fuels.1-3 Hydrogen has been identied as an attractive energy carrier for future energy systems that offers the advantage of clean and complete conversion to water and hydrogen generation from water splitting. It is a strategy to employ solar, wind, ocean currents, tides, or wave energy to water splitting. However, for the development of articial photosynthetic systems for hydrogen generation from water splitting in a sustainable manner, rst it is necessary to synthesize a stable, low-cost, efcient, environmentally friendly and easy to use catalyst for water oxidation, which is the more challenging half reaction of water splitting.4-8
The water-oxidizing complex (WOC) of photosystem II (PSII) is the only system to catalyze water oxidation in nature.9,10 The WOC is a Mn-Ca cluster housed in a protein environment in PSII that controls reaction coordinates, proton movement, and water access. Recently, Shen and coworkers have reported the crystal structure of the Mn-Ca cluster at an atomic resolution (Figure 701).11 In this structure, metal ions, one Ca and four Mn ions, are bridged by ve oxygen atoms. Furthermore, four water molecules were found in this
structure, and two of them were suggested as being substrates for water oxidation (Figure 701).
