Solar fuels editorial.

Every major change in the living standards for humans on our planet has had an energy revolution at its heart – the advent of the industrial age with the steam engine and use of coal, the internal combustion engine and large-scale electricity generation. The energy demand, primarily from emerging economies, will double by 2050. The countervailing urgency of the threat of climate change requires a major shift in our energy sourcing, creating four new trends that will shape the current century: electrification, decarbonization, localization, and optimization. One of the ‘‘holy grails’’ of 21st century science is the economical conversion of solar energy into chemical fuels. Research targeting efficient utilization of solar energy is inherently interdisciplinary, involving inorganic and organic synthesis, solid state chemistry and physics, electrochemistry, chemical kinetics and mechanism, and theoretical and computational chemistry. Solar fuels production involves three basic components: light absorption; charge transport; and multielectron redox catalysis. This themed issue brings together some of the world’s foremost experts to discuss current research and future prospects in this area. In ‘‘Long-lived charge separated states in nanostructured semiconductor photoelectrodes for the production of solar fuels’’, Cowan and Durrant (DOI: 10.1039/C2CS35305A) discuss designs to increase charge carrier lifetimes in semiconductor photoelectrodes for water photolysis and carbon dioxide reduction that are based on lessons learned from natural photosynthesis. A key consideration is the design of interfaces that achieve a sufficient increase in charge carrier lifetime with a high quantum yield, whilst minimizing the energy loss associated with this lifetime gain. Osterloh (DOI: 10.1039/C2CS35266D) reviews the current state of research on nanoscale-enhanced photoelectrodes and photocatalysts in ‘‘Inorganic nanostructures for photoelectrochemical and photocatalytic water splitting’’. The effects of nanostructuring on carrier generation and collection, multiple exciton generation, and quantum confinement, as well as implications of particle size on surface recombination, the size of space charge layers, and on the possibility of controlling nanostructure energetics via potential determining ions, are described. In ‘‘Nanostructured photoelectrodes based on WO3: applications to photooxidation of aqueous electrolytes’’, Bignozzi, Caramori, Cristino, Argazzi, Meda and Tacca (DOI: 10.1039/ C2CS35373C) focus on the preparation and modification of nanostructured WO3 thin films for photoanodes. WO3 is one of the few materials that can achieve efficient water photo-oxidation under visible illumination, stably operating under strongly oxidizing conditions; achieving almost quantitative photon to electron conversion. Park, McDonald and Choi (DOI: 10.1039/C2CS35260E) report on ‘‘Progress in bismuth vanadate photoanodes for use in solar water oxidation’’. Latest efforts to improve performance include morphology control, formation of composite structures, composition tuning, and coupling of oxygen evolution catalysts, and are directly applicable to the understanding and improvement of other photoelectrode systems. Artero and Fontecave (DOI: 10.1039/ C2CS35334B) give us their perspective on ‘‘Solar fuels generation and molecular systems: is it homogeneous or heterogeneous catalysis?’’ While allowing for fine tuning of catalytic properties through ligand design, molecular approaches are frequently criticized because of the inherent fragility of the resulting catalysts when exposed to extreme redox potentials. In a number of cases the true catalytic species is heterogeneous arising from the transformation of the initial molecular pre-catalyst. In their review, they discuss cases in which this issue has been directly addressed, similar to homogeneous hydrogenation reactions in organometallic chemistry. In ‘‘Design and development of photoanodes for water-splitting dye-sensitized photoelectrochemical cells’’, Swierk and Mallouk (DOI: 10.1039/C2CS35246J) discuss dye sensitized solar cells (DSSCs) that use low-cost materials, feature tunable molecular sensitizers, and exhibit quantum efficiencies near unity. These features can be exploited by functionalizing DSSCs with catalysts for water oxidation and reduction. California Institute of Technology, Pasadena, California 91125, USA † Part of the solar fuels themed issue. DOI: 10.1039/c3cs90016a