Nature offers inspiration for developing technologies that integrate the capture, conversion, and storage of solar energy. In this review article, we highlight principles of natural photosynthesis and artificial photosynthesis, drawing comparisons between solar energy transduction in biology and emerging solar-to-fuel technologies. Key features of the biological approach include use of earth-abundant elements and molecular interfaces for driving photoinduced charge separation reactions that power chemical transformations at global scales. For the artificial systems described in this review, emphasis is placed on advancements involving hybrid photocathodes that power fuel-forming reactions using molecular catalysts interfaced with visible-light-absorbing semiconductors. CONTENTS1. Introduction 16051 2. Photochemistry, Photoelectrochemistry, Photocatalysis, Photosynthesis, Photoelectrosynthesis, and Efficiencies 16052 3. Natural Photosynthesis 16053 4. From Enzymes to Human-Engineered Catalysts 16056 5. Artificial Photosynthesis and Photoelectrosynthetic Cells 16056 6. Molecular-Catalyst-Modified Semiconductors 16059 7. Examples Involving Solid-State Photocathodes Modified with Molecular Catalysts 16060 7.1. Photoelectrochemical H 2 Production 16060 7.2. Photoelectrochemical CO 2 Reduction 16075 8. Examples Involving Light-Absorbing Nanoparticles and Nanorods Modified with Molecular Catalysts 16080 8.1. Molecular-Catalyst-Modified Semiconductor Nanoparticles and Nanorods for H 2 Production 16080 8.2. Molecular-Catalyst-Modified Semiconductor Nanoparticles and Nanorods for CO 2 Reduction 16082 9.
In this study, a light sensor is fabricated based on photosystem I (PSI) and a graphene field-effect transistor (FET) that detects light at a high quantum yield under ambient conditions. We immobilized PSI on a micrometer-sized graphene FET using Au nanoparticles (AuNPs) and measured the I–V characteristics of the modified graphene FET before and after light irradiation. The source–drain current (I sd) increased upon illumination, exhibiting a photoresponsivity of 4.8 × 102 A W–1, and the charge neutrality point of graphene shifted by −12 mV. This system represents the first successful photosensing system based on proteins and a solution-gated graphene FET. The probable mechanism of this negative shift can be explained by the increase in negative charge carriers in graphene induced by a hole trap in the AuNP resulting from electron transfer from the AuNP to PSI. Photoresponses were only observed in the presence of two surface-active agents, n-hexyltrimethylammonium bromide and sodium dodecylbenzenesulfonate, because they caused the formation of a hydrophobic environment on the surface of the graphene. The lipid layer of these agents caused dissociation of ascorbate ions from the graphene sheet, thereby expanding the Debye screening length of the electrolyte solution. The hydrophobic environment above graphene also enhanced hole storage in the AuNP through electron transfer from the AuNP to PSI.
In this special collection dedicated to Prof. Jean‐Michel Savéant, we report on the synthesis and characterization of a novel binuclear Fe(III) fused porphyrin. Ultraviolet‐visible spectroscopy confirms the extended electronic structure of this macrocycle. In addition, Fourier transform infrared spectroscopy indicates the Fe centers experience a relatively rigid ligand environment as compared to a structurally related mononuclear complex featuring an 18 π‐aromatic porphyrin ligand. X‐ray photoelectron and X‐ray absorption near edge spectroscopies confirm the iron centers of both assemblies are Fe(III) in the as prepared, resting state. In comparison with the mononuclear porphyrin, electrochemical measurements show there is a doubling of the number of redox events associated with the fused, binuclear complex. In summary, key features of the fused‐iron‐porphyrin include: 1) bimetallic‐iron sites, 2) a π‐extended ligand capable of delocalizing electrons across the multimetallic scaffold, and 3) the ability to store up to six electrons.
Photosystem II (PSII)-modified gold electrodes were prepared by the deposition of PSII reconstituted with platinum nanoparticles (PtNPs) on Au electrodes. PtNPs modified with 1-[15-(3,5,6-trimethyl-1,4-benzoquinone-2-yl)]pentadecyl disulfide ((TMQ(CH)S)) were incorporated into the Q site of PSII isolated from thermophilic cyanobacterium Thermosynechococcus elongatus. The reconstitution was confirmed by Q-reoxidation measurements. PSII reconstituted with PtNPs was deposited and integrated on a Au(111) surface modified with 4,4'-biphenyldithiol. The cross section of the reconstituted PSII film on the Au electrode was investigated by SEM. Absorption spectra showed that the surface coverage of the electrode was about 18 pmol PSII cm. A photocurrent density of 15 nAcm at E = +0.10 V (vs Ag/AgCl) was observed under 680 nm irradiation. The photoresponse showed good reversibility under alternating light and dark conditions. Clear photoresponses were not observed in the absence of PSII and molecular wire. These results supported the photocurrent originated from PSII and moved to a gold electrode by light irradiation, which also confirmed conjugation with orientation through the molecular wire.
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