Hybrid Artificial Photosynthetic Systems Comprising Semiconductors as Light Harvesters and Biomimetic Complexes as Molecular Cocatalysts

Abstract

S olar fuel production through artificial photosynthesis may be a key to generating abundant and clean energy, thus addressing the high energy needs of the world's expanding population. As the crucial components of photosynthesis, the artificial photosynthetic system should be composed of a light harvester (e.g., semiconductor or molecular dye), a reduction cocatalyst (e.g., hydrogenase mimic, noble metal), and an oxidation cocatalyst (e.g., photosystem II mimic for oxygen evolution from water oxidation). Solar fuel production catalyzed by an artificial photosynthetic system starts from the absorption of sunlight by the light harvester, where charge separation takes place, followed by a charge transfer to the reduction and oxidation cocatalysts, where redox reaction processes occur. One of the most challenging problems is to develop an artificial photosynthetic solar fuel production system that is both highly efficient and stable. The assembly of cocatalysts on the semiconductor (light harvester) not only can facilitate the charge separation, but also can lower the activation energy or overpotential for the reactions. An efficient light harvester loaded with suitable reduction and oxidation cocatalysts is the key for high efficiency of artificial photosynthetic systems.In this Account, we describe our strategy of hybrid photocatalysts using semiconductors as light harvesters with biomimetic complexes as molecular cocatalysts to construct efficient and stable artificial photosynthetic systems. We chose semiconductor nanoparticles as light harvesters because of their broad spectral absorption and relatively robust properties compared with a natural photosynthesis system. Using biomimetic complexes as cocatalysts can significantly facilitate charge separation via fast charge transfer from the semiconductor to the molecular cocatalysts and also catalyze the chemical reactions of solar fuel production. The hybrid photocatalysts supply us with a platform to study the photocatalytic mechanisms of H 2 /O 2 evolution and CO 2 reduction at the molecular level and to bridge natural and artificial photosynthesis. We demonstrate the feasibility of the hybrid photocatalyst, biomimetic molecular cocatalysts, and semiconductor light harvester for artificial photosynthesis and therefore provide a promising approach for rational design and construction of highly efficient and stable artificial photosynthetic systems.

Morphology‐Controlled Self‐Assembly and Nanostructured NiO: An Efficient and Robust Photocatalytic Water‐Oxidation Catalyst

“…The reactionw as performed by photoirradiation (l ! 420 nm) of ab orate buffer (80 mm, pH 8.5, 15 mL) containing aN iO catalyst, Na 2 [15] for which the electrode potential is higher than that of Ru(bpy [16] can furthero xidize another Scheme1.Principalprocesses of O 2 evolution in al ight-driven water-oxidation system. WOC = water-oxidation catalysts.…”

“…[1] The overall photocatalytic water-splitting reaction involves three major steps for molecular-basedp hotocatalytic systems: 1) absorption of light by ap hotosensitizert o generatet he excited-state sensitizer for solar-energy harvesting and utilization, 2) water oxidation that extracts electrons and protons, and 3) reduction of protons or the conversion of CO 2 into hydrocarbon fuels by using the protons generated during the second step. [2] Photocatalytic reactions could be realized if these three sequential steps are completed. To make this artificial system economically viable, the use of minor or preciousm etals in each step should be avoided.…”

Integration of [(Co(bpy)3]2+ Electron Mediator with Heterogeneous Photocatalysts for CO2 Conversion

“…During the photocatalytic process, electron-hole pairs are created in semiconductors upon light irradiation and the generation of labile intermediates. [33] Unstable intermediates are readily converted into end products. It is believed that desirable active performance can be accomplished only if the free energy (DG) is surmounted.…”

Multi‐Electron Oxygen Reduction by a Hybrid Visible‐Light‐Photocatalyst Consisting of Metal‐Oxide Semiconductor and Self‐Assembled Biomimetic Complex

“…A fascinating approach is the hybridization of metal oxide semiconductors exhibiting a strong absorption in the wide spectral range and molecular metal complexes with highly efficient and selective electrocatalytic activity. [6,7] Although this type of hybrid photocatalysts has recently attracted much interest for H 2 generation, [8] CO 2 reduction, [9,10] and environmental purification, [11] …”

“…On the other hand, the direct copper complex-BiVO 4 bonding and the concentration of O 2 near the surface enable the rapid electron transfer from the CB of BiVO 4 to O 2 in the OBBC through the copper ions. [7,22] Consequently, the multielectron reduction of O 2 efficiently proceeds through the pair of Cu ions in the OBBC, being accompanied by the coupling with H + . H 2 O 2 was not detected from the solutions after the reaction.…”