Ultrathin oxide layers for nanoscale integration of molecular light absorbers, catalysts, and complete artificial photosystems

Artificial photosynthesis is an attractive approach for the generation of renewable fuels because such systems will be suitable for deployment on highly abundant, non-arable land. Recently emerged methods of nanoscience to create conformal, ultrathin oxide layers enable the hierarchical integration of light absorbers, catalysts, and membranes into systems with far simpler synthetic approaches than available till now. This holds in particular for the coupling of molecular light absorbers and catalysts for sunlight to fuel conversion, providing photoelectrodes with greatly improved stability. Moreover, the use of ultrathin inert oxides as proton conducting, molecule impermeable membranes has opened up the integration of reduction and oxidation half reactions into complete photosynthetic systems on the shortest possible length scale—the nanometer scale. This capability affords minimization of energy-degrading resistance losses caused by ion transport over macroscale distances while separating the incompatible water oxidation and carbon dioxide reduction catalysis environments on the nanoscale. Understanding of charge transport between molecular components embedded in the oxide layers is critical for guiding synthetic design improvements of the light absorber-catalyst units to optimize performance and integrate them into complete artificial photosystems. Recent results and insights from transient optical, vibrational, and photoelectrochemical studies are presented, and future challenges and opportunities for engaging dynamic spectroscopies to accelerate the development of nanoscale integrated artificial photosystems are discussed.