Artificial photosynthesis systems for catalytic water oxidation

The consumption of fossil fuel energy and the resulting environmental pollution have incentivized scientists to attempt to develop renewable, reliable and continuously available energy sources. Solar water splitting to produce hydrogen is one of the effective ways to solve the energy and environmental problems. Water oxidation (2H(2)O -> 4H(+) + 4e(-) + O-2), as one half of the water-splitting reaction, is the primary reaction of both natural and artificial photosynthesis, thus the development of highly active and robust water oxidation catalysts (WOCs) is extremely important for constructing a sustainable artificial photosynthesis system for solar energy conversion. Molecular catalysts and inorganic nanoparticles, as representatives of homogeneous and heterogeneous catalysts, have their respective advantages and have been widely studied. Moreover, hybrid systems combining the molecular catalysts and inorganic nanoparticles, exhibit unique advantages for water oxidation and bridge the gap between homogeneous catalysis and heterogeneous catalysis. Despite significant efforts made so far, a practically viable catalytic system with sufficient efficiency, stability and low cost is yet to be demonstrated. The present topic mainly focuses on the recent advances on different types of WOCs that are generally screened out by several evaluating approaches, such as chemical water oxidation, electrocatalytic water oxidation and photo(electro)catalytic water oxidation. Furthermore, understanding the water oxidation mechanism, including elucidation of the role of active intermediates during the water oxidation process, is helpful to develop more efficient WOCs.