Solar fuel production: Strategies and new opportunities with nanostructures

The photocatalytic and photoelectrochemical reduction of water or CO2 is an intriguing approach to producing sustainable solar fuels, and has attracted growing and intense interest. Nanostructuring of photocatalysts and photoelectrodes has been proven to be a strong strategy to dramatically improve overall solar-to-fuel conversion efficiencies. Another technological barrier for the practical implementation of solar fuel production is long-term material durability, which has recently been well addressed through use of conformal coatings of protective layers onto the narrow band-gap semiconductors that are suitable for efficient solar-to-fuel conversions but photoelectrochemically unstable. These significant progresses may lead us to the practical implementation of solar fuel production. In this review, we will focus on these exciting progresses achieved using nanostructuring strategies, specifically regarding how the nanostructure influences the charge transport and separation; special attention wilt be paid to how a nanoscale coating (overlayer) passivates the surface states, thereby reducing the surface electron hole recombination, and how a nanoscale coating (protective layer) prevents the photocorrosion or photopassivation of the semiconductors with optimal band gaps. We hope that the design strategies using these nanostructures will offer new and greater opportunities for efficient solar fuel production to existing photocatalytic and photoelectrochemical systems. (C) 2015 Elsevier Ltd. All rights reserved.