Commercial P25 modified by Au-Cu alloy nanoparticles as thin film exhibits, for CO2 reduction by water under sun simulated light, a rate of methane production above 2000 μmol (g of photocatalyst)(-1) h(-1). Although evolution of hydrogen is observed and O2 and ethane detected, the selectivity of conduction band electrons for methane formation is almost complete, about 97%. This photocatalytic behavior is completely different from that measured for Au/P25 (hydrogen evolution) and Cu/P25 (lower activity, but similar methane selectivity). Characterization by TEM, XPS, and UV-vis spectroscopy shows that Au and Cu are alloyed in the nanoparticles. FT-IR spectroscopy and chemical analysis have allowed one to detect on the photocatalyst surface the presence of CO2(•-), Cu-CO, and elemental C. Accordingly, a mechanism in which the role of Au is to respond under visible light and Cu binds to CO and directs the reduction pathway is proposed.

The reduction of carbon dioxide to useful chemicals has received a great deal of attention as an alternative to the depletion of fossil resources without altering the atmospheric CO2 balance. As the chemical reduction of CO2 is energetically uphill due to its remarkable thermodynamic stability, this process requires a significant transfer of energy. Achievements in the fields of photocatalysis during the last decade sparked increased interest in the possibility of using sunlight to reduce CO2. In this review we discuss some general features associated with the photocatalytic reduction of CO2 for the production of solar fuels, with considerations to be taken into account of the photocatalyst design, of the limitations arising from the lack of visible light response of titania, of the use of co-catalysts to overcome this shortcoming, together with several strategies that have been applied to enhance the photocatalytic efficiency of CO2 reduction. The aim is not to provide an exhaustive review of the area, but to present general aspects to be considered, and then to outline which are currently the most efficient photocatalytic systems.

Fuel cells are devices that transform efficiently the chemical energy of hydrogen or another fuel into clean electricity. The fuel cells technology is attractive for its high-energy efficiency and expanded...