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Metalloporphyrin-modified semiconductors for solar fuel production.

ABSTRACT: We report a direct one-step method to chemically graft metalloporphyrins to a visible-light-absorbing gallium phosphide semiconductor with the aim of constructing an integrated photocathode for light activating chemical transformations that include capturing, converting, and storing solar energy as fuels. Structural characterization of the hybrid assemblies is achieved using surface-sensitive spectroscopic methods, and functional performance for photoinduced hydrogen production is demonstrated via three-electrode electrochemical testing combined with photoproduct analysis using gas chromatography. Measurements of the total per geometric area porphyrin surface loadings using a cobalt-porphyrin based assembly indicate a turnover frequency ≥3.9 H₂ molecules per site per second, representing the highest reported to date for a molecular-catalyst-modified semiconductor photoelectrode operating at the H⁺/H₂ equilibrium potential under 1-sun illumination.

SUBMITTER: Khusnutdinova D

PROVIDER: S-EPMC5355850 | biostudies-literature | 2017 Jan

REPOSITORIES: biostudies-literature

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Metalloporphyrin-modified semiconductors for solar fuel production.

Khusnutdinova D D Beiler A M AM Wadsworth B L BL Jacob S I SI Moore G F GF

Chemical science 20160805 1

We report a direct one-step method to chemically graft metalloporphyrins to a visible-light-absorbing gallium phosphide semiconductor with the aim of constructing an integrated photocathode for light activating chemical transformations that include capturing, converting, and storing solar energy as fuels. Structural characterization of the hybrid assemblies is achieved using surface-sensitive spectroscopic methods, and functional performance for photoinduced hydrogen production is demonstrated < ...[more]

PMID: 28451172

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Project description:Most chemical reactions promoted by light and using a photosensitizer (a dye) are subject to the phenomenon of luminescence. Redistribution of light in all directions (isotropic luminescence emission) and in a new spectral range (luminescence emission spectrum) makes experimental and theoretical studies much more complex compared to a situation with a purely absorbing reaction volume. This has a significant impact on the engineering of photoreactors for industrial applications. Future developments associated with photoreactive system optimization are therefore extremely challenging, and require an in-depth description and quantitative analysis of luminescence. In this study, a radiative model describing the effect of luminescence radiation on the calculation of absorptance is presented and analyzed with the multiple inelastic-scattering approach, using Monte Carlo simulations. The formalism of successive orders of scattering expansion is used as a sophisticated analysis tool which provides, when combined with relevant physical approximations, convenient analytical approximate solutions. Its application to four photosensitizers that are representative of renewable hydrogen production via artificial photosynthesis indicates that luminescence has a significant impact on absorptance and on overall quantum yield estimation, with the contribution of multiple scattering and important spectral effects due to inelastic scattering. We show that luminescence cannot be totally neglected in that case, since photon absorption lies at the root of the chemical reaction. We propose two coupled simple and appropriate analytical approximations enabling the estimation of absorptance with a relative error below 6% in every tested situation: the zero-order scattering approximation and the gray single-scattering approximation. Finally, this theoretical approach is used to determine and discuss the overall quantum yield of a bio-inspired photoreactive system with Eosin Y as a photosensitizer, implemented in an experimental setup comprising a photoreactor dedicated to hydrogen production.

Project description:Dye-sensitisation of TiO2 and other metal oxides is an established strategy to couple solar light harvesting with efficient charge separation for the production of electricity in dye-sensitised solar cells (DSCs) or fuels in dye-sensitised semiconductor photocatalysis (DSP). Perylene monoimide (PMI) dyes have emerged as promising organic dyes, but they have not previously been used in a functional assembly with TiO2 in aqueous solution. Here, five novel PMI dyes bearing carboxylic acid, phosphonic acid, acetylacetone, hydroxyquinoline or dipicolinic acid anchoring groups for attachment onto TiO2 are reported. We identified functional DSC and DSP systems with PMI-sensitised TiO2 in aqueous solution, which permitted a side-by-side comparison with respect to performance between the two systems. Structure-activity relationships allowed us to suggest anchor-condition-system associations to suit specific anchoring groups at various pH values, and with different electron mediators (redox couple or sacrificial electron donor) and catalysts in DSC and DSP schemes. A DSC sensitised with the hydroxyquinoline-modified PMI dye reached the highest short-circuit current density (J SC ≈ 1.4 mA cm-2) in aqueous electrolyte solution during irradiation with simulated solar light. This dye also achieved a turnover number (TONPMI) of approximately 4900 for sacrificial proton reduction after 24 h irradiation in a DSP scheme with Pt as a H2-evolving co-catalyst at pH 4.5. This performance was only surpassed by the carboxylic acid-bearing dye, which reached a new benchmark turnover number (TONPMI ≈ 1.1 × 104 after 72 h) for an organic dye in nanoparticulate DSP for solar fuel production. At higher pH (8.5), our results showed that the phosphonic acid group allows for higher performance due to a stronger anchoring ability. This study provides a platform for aqueous PMI dye-sensitised TiO2 chemistry and gives valuable insights into the performance of different anchoring groups in DSC and DSP systems.

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Metalloporphyrin-modified semiconductors for solar fuel production.

Publications

Metalloporphyrin-modified semiconductors for solar fuel production.

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