No abstract

Photocatalytic reduction of carbon dioxide can activate chemically inert carbon dioxide by the use of renewable energy. In the present work, the main products of photocatalytic reduction of CO 2 in aqueous TiO 2 suspensions were found to be methane, methanol, formaldehyde, carbon monoxide, and H 2 . Anatase TiO 2 catalysts with various morphologies, such as nanoparticle, nanotube, and nanosheet, were synthesized through a hydrothermal method. The TiO 2 nanosheets were more active than the nanotubes or nanoparticles in the reduction of CO 2 in aqueous solution. This is because the photogenerated carriers prefer to flow to the specific facets. The TiO 2 sheet with high-energy exposed {001} facets facilitates the oxidative dissolution of H 2 O with photogenerated holes, leaving more photogenerated electrons available for the reduction of CO 2 on {101} facets. Moreover, surface fluorination promotes the formation of Ti 3+ species, which is helpful in the reduction of CO 2 to CO 2 − and in extending the lifetime of photogenerated electron−hole pairs. The optimum ratio of exposed {001} to {101} facets for surface-fluorinated TiO 2 nanosheets was found to be ∼72:28, which corresponds to an initial F/Ti ratio of 1. From our analysis of the effect of adding of known intermediates on the photocatalytic reduction of CO 2 , we propose that the photocatalytic reduction of CO 2 with H 2 O on surface-fluorinated TiO 2 nanosheets proceeds via a mechanism involving generation of hydrogen radicals and carbon radicals.

All‐perovskite tandem solar cells offer a promising avenue to go beyond the efficiency limit of single‐junction devices. Their efficiencies have been increasing rapidly in the past few years; however, their commercial viability is hindered by the instability under thermal stressing. Herein, comprehensive device design strategies are proposed to achieve thermally stable all‐perovskite tandem solar cells while retaining the advantages of solution processing. Metal oxides, i.e., NiOx and SnO2, are used for the hole and electron transport layers in both wide bandgap and narrow subcells. The metal‐based recombination layer is replaced with a stable and conductive indium tin oxide nanocrystals film to fabricate an all metal‐oxide‐based tunnel junction. Based on those design strategies, the encapsulated all‐perovskite tandem solar cells retained 85% of their initial efficiency after stressing at 85 °C for 2500 h and maintained >80% of their initial performance after 900 h operation at the maximum power point and operating temperature of ≈65 °C. Achieving such thermal stability represents a crucial step toward commercial viability of all‐perovskite tandem solar cells.