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

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What Nanoporous Supports Do We Need for Solar
Light-Driven Fuel Synthesis
Direct Solar to Fuel by Solid Photocatalysts Pri
nciple
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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, gt 400 hours
• ? Direct solar to fuel works with UV light

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Direct Solar to Fuel by Solid Photocatalysts
Where we are UV light-driven CO2 reduction by
H2O Isolated Ti centers in nanoporous silicate
Anpo, Catal. Today 1998, 44, 327 Frei, J. Phys.
Chem. B 2004, 108, 18269

• ? Direct Solar to Fuel Works with UV Light

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Direct Solar to Fuel by Solid
Photocatalysts Where we are Visible
light-driven H2O ? H2 O2
Single Component mixed metal oxide NiInTaO3
Two-component mixed metal oxide with shuttle
(Z-scheme)
Q.Y. 0.3 at 420 nm Arakawa, Science 2001, 414,
625
Q.Y. 0.3 at 500 nm Kudo, Chem. Commun. 2001,
2416

• Water splitting with visible light observed, but
  very low efficiency.

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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
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What we need

• Fact
• Numerous small bandgap semiconductor
  photocatalysts work efficiently under visible
  light (?gt600 nm, q.y.gt50), 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

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What Active Molecular Components are
AvailableSome Examples
Organometallic

• Ru(bpy)32 sensitizer/ Ni(cyclam) catalyst
  (CO2 to CO, H2O reduction)
• Inorganic
• IrOx Clusters (H2O oxidation)
• MMCT units (CO2 splitting)

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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
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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
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Solar to Fuel by Solid PhotocatalystsWhat 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