Artificial photosynthesis cint 0711-2010

Editor's Notes

• #35: Growing a particular CBI structure at different temperatures give different, but related morphologies.Different CBI materials (i.e., Sn/Zn and Zn/Sn materials) give the same morphology, but at different growth temperatures.Example: Zn/Sn clovers obtained at 80 ○C have the same morphology as the Sn/Zn clovers obtained at room temperature.Changing the growth temperature changes like the diffusion rate and solubility of the CBI materials. These parameters alter the diffusion limited crystal growth processes that produce these snowflake-like CBI structures.
• #38: Most important, the properties of the of the CBI structures can be selected by choice of metals—without significantly altering the molecularpacking. Nature of metals in cores has little influence on the crystal structure and morphology. The metals in the core macrocycles determine their individual optoelectronic or catalytic properties. A variety of binary combinations of metals can be coupled in the CBI materials to provide a range of opto-electronic and catalytic functions of the CBI materials.For example, the Zn/Sn clovers are photoconductors.
• #52: The Zn/Sn clovers, already shown to be photoconductive, are also photocatalytic.When irradiated with visible light, the photocatalytic reduction of platinum complex to Pt metal initiates the growth of many seed nanoparticles that continue to grow dendritically by photocatalytic and autocatalytic reduction of Pt complex and oxidation of ascorbic acid.This is important because we can use the CBI nanostructures own photocatalytic properties to generate CBI structure-metal nanocomposites that are required for our artificial photosynthesis system.Under the same solution conditions and light exposure, the CBI structure should harvest the light energy to photocatalytically reduce water to hydrogen in the absence of the Pt complex.Although hydrogen is required for Fischer-Tropsch reaction to produce liquid fuels, it is not the main target of our artificial photosynthesis system.Photocatalytic activity allows us the add nanoscale metal components as electronic conductors or catalysts—CBI nanostructure-metal nanocomposites
• #58: Electrochemical CO2 reduction:Off and on for a several decades, we have been investigating electrochemical CO2 reduction to CO using cobalt porphyrin electrocatalysts. CO is an important and valuable intermediate to the production of carbon-based liquid fuels. For example, the Fischer-Tropsch reaction uses CO and H2 as feedstocks to produce methane, methanol, and higher hydrocarbon fuels.We have also been using Sn porphyrins and Sn porphyrin nanostructures to photosynthesize H2 using visible light, giving us both of the feedstocks for the Fischer-Tropsch reaction. The Co porphyrin was simply adsorbed onto carbon gas diffusion electrodes in a polycrystalline form. The thermodynamic potential for the reaction: CO2 (g) + 2H+ + 2e- -> CO + H2O is -0.52 V (NHE) or -0.75 V (Ag/AgCl).The current voltage curve for the reaction shows that the reaction requires a potential of at least ‑0.75 V (vs. Ag/AgCl) to reduce CO2 almost exclusively to CO. The current efficiency for the CO2 (g) + 2H+ + 2e- -> CO + H2O reaction can be as high as 80%. Photoelectrochemical CO2 reduction:For our nanoengineeredCoTPP-modified gas diffusion electrodes, a visible light-induced increase in catalysis is observed but the potential at which reduction occurs is virtually unchanged.Adding SnTPP (photocatalyst) to the CoTPP electrode does not have a significant effect. Photocatalytic CO2 reduction:Apparently requires better coupling between the photocatalyst (SnP, ZnP) and the CO2-reduction catalyst (CoP).Our quantum computation studies have identified low energy intermediates of the reaction and point to a Co(I)-CO2 complex as the active species when in an aqueous environment. The reaction can be photoassisted by coupling a photoexcited electron donor with the Co porphyrin catalyst. The excited electron donor should be able to reduce Co(III) porphyrin to the Co(I) species for solar assisted CO2 reduction.Need better coupling of harvested solar energy with chemical catalysts.
• #96: Electrochemical CO2 reduction:Off and on for a several decades, we have been investigating electrochemical CO2 reduction to CO using cobalt porphyrin electrocatalysts. CO is an important and valuable intermediate to the production of carbon-based liquid fuels. For example, the Fischer-Tropsch reaction uses CO and H2 as feedstocks to produce methane, methanol, and higher hydrocarbon fuels.We have also been using Sn porphyrins and Sn porphyrin nanostructures to photosynthesize H2 using visible light, giving us both of the feedstocks for the Fischer-Tropsch reaction. The Co porphyrin was simply adsorbed onto carbon gas diffusion electrodes in a polycrystalline form. The thermodynamic potential for the reaction: CO2 (g) + 2H+ + 2e- -> CO + H2O is -0.52 V (NHE) or -0.75 V (Ag/AgCl).The current voltage curve for the reaction shows that the reaction requires a potential of at least ‑0.75 V (vs. Ag/AgCl) to reduce CO2 almost exclusively to CO. The current efficiency for the CO2 (g) + 2H+ + 2e- -> CO + H2O reaction can be as high as 80%. Photoelectrochemical CO2 reduction:For our nanoengineeredCoTPP-modified gas diffusion electrodes, a visible light-induced increase in catalysis is observed but the potential at which reduction occurs is virtually unchanged.Adding SnTPP (photocatalyst) to the CoTPP electrode does not have a significant effect. Photocatalytic CO2 reduction:Apparently requires better coupling between the photocatalyst (SnP, ZnP) and the CO2-reduction catalyst (CoP).Our quantum computation studies have identified low energy intermediates of the reaction and point to a Co(I)-CO2 complex as the active species when in an aqueous environment. The reaction can be photoassisted by coupling a photoexcited electron donor with the Co porphyrin catalyst. The excited electron donor should be able to reduce Co(III) porphyrin to the Co(I) species for solar assisted CO2 reduction.Need better coupling of harvested solar energy with chemical catalysts.