WFU Joint Chemistry and Physics Colloquium

TITLE: Sunlight-to-Fuel Energy Conversion Using Cu(I)-Containing Oxide Semiconductors

SPEAKER: Professor Paul A. Maggard,

TIME: Wednesday April 10, 2013 at 4:00 PM

PLACE: Room 101 Olin Physical Laboratory

The conversion of solar energy to chemical fuels, e.g., the renewable production of hydrogen or methanol, has attracted intense research interest as both a practical and environmentally responsible way to meet our growing energy needs. The photoelectrochemical reduction of water to hydrogen can be facilitated using p-type semiconducting films, such as previously known for crystalline III-V semiconductors. Our research efforts focus on a promising new class of p-type semiconductors found in the Cu(I)-tantalate and Cu(I)-niobate systems, e.g., CuNb₃O₈ and Cu₃Ta₇O₁₉, that exhibit bandgap sizes spanning the visible-light energies. Measurements of their conduction-band energies show that these are located at suitable energies (from approximately .0.6 V to .1.5 V at pH = 6.3) for driving fuel-producing reduction reactions at their surfaces. A new nanoparticle synthetic strategy for these semiconductors will be presented that involves the use of Li₃NbO4 nanoparticles and solvothermally-mediated copper(I)-exchange reactions. In addition, the new metastable Cu₂Nb₈O₂₁ will be described that must be prepared at low temperatures from nanoparticle precursors owing to an instability to a disproportionation reaction at its surfaces. The relationship of this nanoparticle instability to a surface nanostructuring of polycrystalline films of Cu(I)-niobates and Cu(I)-tantalates (when heated to relatively low temperatures) will also be explored within this presentation. Importantly, the latter effect can lead to a very strong enhancement of the cathodic photocurrents for the reduction of water to hydrogen for some of these Cu(I)-containing semiconductors. These results will also be placed within a broader context that involves the requirements of combining photon absorption, charge-carrier transport, and catalyst turnover in sunlight-to-fuel energy conversion schemes.