High-potential Porphyrin-based SnO2 Photoanodes for Water Photooxidation
Francesca Tessore a, Gabriele Di Carlo a, Alessio Orbelli Biroli b, Elisabetta Benazzi c, Stefano Caramori c
a Dipartimento di Chimica, Università degli Studi di Milano
b Istituto di Scienze e Tecnologie Molecolari del CNR (CNR-ISTM), via Golgi, 19, Milan, 20133, Italy
c Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Ferrara, via Fossato di Mortara 17, Ferrara, 44121, Italy
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Oral, Francesca Tessore, presentation 112
DOI: https://doi.org/10.29363/nanoge.hopv.2019.112
Publication date: 11th February 2019

Porphyrins are very promising light harvesters for molecular water splitting (WS) [1-3], due to the strong UV-Vis absorptions, the high electrochemical and photochemical stability, the electronic properties which can be tuned quite easily through appropriate structural modifications [4-6]. A well-established approach for the preparation of porphyrins with potential high enough to allow water oxidation is to endow the macrocycle with electron-withdrawing groups, to induce an electron deficiency that leads to a positive shift in the ground state oxidation potential, so that the holes remaining on the photooxidized porphyrin are thermodynamically capable of driving water oxidation [3].

We have prepared some ß-substituted A4-type and meso-substituted A3B- type ZnII porphyrins, carrying pentafluorophenyl moieties and different pi-spacers and anchoring groups. The compounds have a calculated HOMO-LUMO energy gap of ∼2.2 eV with a E0red/E0ox potential of ∼0.7-0.8 V (vs Fc+/Fc), and they have been used to sensitize wide band-gap semiconductors, i.e. TiO2 and SnO2.

A detailed photoelectrochemical characterization of the photoanodes has been carried out, evaluating their performances with hydrobromic and ascorbic acid as sacrificial agents, in order to explore the electronic transfer ability of the dyes in the absence of kinetic barriers which can limit the dye regeneration. The most performing photoanode with respect to charge separation and collection has been functionalized with the efficient binuclear iridium(IV) catalyst reported by Brudvig [7], demonstrating the ability of the substrate to carry out water oxidation, and showing photoinduced production of oxygen with a Faradaic yield equal to 90%.  


The use of instruments purchased through the Regione Lombardia-Fondazione Cariplo joint SmartMatLab Project (Fondazione Cariplo Grant 2013-1766) is gratefully acknowledged.

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