What Nanoporous Supports Do We Need for Solar Light-Driven Fuel Synthesis

1. What Nanoporous Supports Do We Need for Solar Light-Driven Fuel Synthesis Direct Solar to Fuel by Solid Photocatalysts Principle:

2. Direct Solar to Fuel by Solid Photocatalysts Where we are: UV light-driven Water Splitting: mixed metal oxide nanoparticles Kudo, J. Am. Chem. Soc.2003, 125, 3082. Q.Y. = 56%, > 400 hours ● Direct solar to fuel works with UV light

3. Direct Solar to Fuel by Solid Photocatalysts Where we are: UV light-driven CO2 reduction by H2O: Isolated Ti centers in nanoporous silicate ● Direct Solar to Fuel Works with UV Light Anpo, Catal. Today1998, 44, 327 Frei, J. Phys. Chem. B2004, 108, 18269

4. Direct Solar to Fuel by Solid PhotocatalystsWhere we are: Visible light-driven H2O → H2 + O2 Single Component mixed metal oxide NiInTaO3 Two-component mixed metal oxide with shuttle (Z-scheme) • Water splitting with visible light observed, but very low efficiency. Q.Y.= 0.3% at 420 nm Arakawa, Science2001, 414, 625 Q.Y.= 0.3% at 500 nm Kudo, Chem. Commun. 2001, 2416

5. Direct Solar to Fuel by Solid Photocatalysts Where we are: Visible light-driven CO2 Splitting Binuclear photocatalytic sites on inert mesoporous oxide support Frei, J. Am. Chem. Soc. 2005, 127, 1610

6. What we need Fact: Numerous small bandgap semiconductor photocatalysts work efficiently under visible light (λ>600 nm, q.y.>50%), but require sacrificial reagents Lesson: no defects or ill-defined structures can be involved in energy transduction, charge migration, or catalytic transformation because they will invariably lead to loss of stored energy, charge, or chemical selectivity How can we avoid sacrificial reagents: • Active moieties (light harvesting, charge separation, catalytic sites) of molecular makeup • Need 3-D high surface area ‘spectator’ support for the molecular functionalities with precisely arranged (Angstrom) anchoring sites and structural elements for physical separation on the nanometer scale. • Need to remove promptly the redox products from the reactive surface  exploit gas-solid interface

7. What Active Molecular Components are Available:Some Examples Organometallic: Ru(bpy)32+ sensitizer/ Ni(cyclam) catalyst (CO2 to CO, H2O reduction) Inorganic: IrOx Clusters (H2O oxidation) MMCT units (CO2 splitting)

8. Organic/Metal Oxide Hybrid Functionalities on Mesoporous Supports side view top view Challenge: Incorporation of organic and polynuclear transition metal units at preselected sites and defined orientation inside silica wall

9. Mixed Oxide Functionalities on Mesoporous Silica Supports Challenge: Ir oxide patches of defined composition and structure covalently linked to Co-O-Ti units inside mesoporous silica wall

10. Solar to Fuel by Solid Photocatalysts:What needs to be done Develop methods that afford imprinting of molecular components and well-defined metal oxide clusters into walls of mesoporous nonreducible oxide supports at predetermined locations and with defined orientation New types of templates Methods for creating channel patterns with oxidizing/reducing sites Mesoporous membranes Defect-free active component/silica interface Design new catalytic components for coupled H2O oxidation/CO2 reduction