Visible-light photocurrent response of TiO2-polyheptazine hybrids: Evidence for interfacial charge-transfer absorption

Michal Bledowski, Lidong Wang, Ayyappan Ramakrishnan, Oleksiy V. Khavryuchenko, Volodymyr D. Khavryuchenko, P. Carlo Ricci, Jennifer Strunk, Till Cremer, Claudia Kolbeck, Radim Beranek

Research output: Contribution to journalArticlepeer-review

152 Scopus citations

Abstract

We investigated photoelectrodes based on TiO2-polyheptazine hybrid materials. Since both TiO2 and polyheptazine are extremely chemically stable, these materials are highly promising candidates for fabrication of photoanodes for water photooxidation. The properties of the hybrids were experimentally determined by a careful analysis of optical absorption spectra, luminescence properties and photoelectrochemical measurements, and corroborated by quantum chemical calculations. We provide for the first time clear experimental evidence for the formation of an interfacial charge-transfer complex between polyheptazine (donor) and TiO2 (acceptor), which is responsible for a significant red shift of absorption and photocurrent response of the hybrid as compared to both of the single components. The direct optical charge transfer from the HOMO of polyheptazine to the conduction band edge of TiO2 gives rise to an absorption band centered at 2.3 eV (540 nm). The estimated potential of photogenerated holes (+1.7 V vs. NHE, pH 7) allows for photooxidation of water (+0.82 V vs. NHE, pH 7) as evidenced by visible light-driven (λ > 420 nm) evolution of dioxygen on hybrid electrodes modified with IrO2 nanoparticles as a co-catalyst. The quantum-chemical simulations demonstrate that the TiO 2-polyheptazine interface is a complex and flexible system energetically favorable for proton-transfer processes required for water oxidation. Apart from water splitting, this type of hybrid materials may also find further applications in a broader research area of solar energy conversion and photo-responsive devices.

Original languageEnglish
Pages (from-to)21511-21519
Number of pages9
JournalPhysical Chemistry Chemical Physics
Volume13
Issue number48
DOIs
StatePublished - 28 Dec 2011
Externally publishedYes

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