Application of Solar Energy Conversion

Topic: Characterization of degradation pathways of supra molecular photocatalysts under repair with HPLC

Background

• Photocatalytic water splitting with supra molecular photocatalysts leads to formation of hydrogen using visible light
• Long term catalytic activity is hampered by limited TON’s (upto 500) and life times of active catalysis of 48 h max.
• Analysis of degradation products at the endpoint of catalysis have revealed that the catalyst is intact but the bridging ligand hydrogenated
• Reoxidation of the bridging ligand with 1O2 was accomplished and lead to regeneration of the photocatalytic activity
• Successive repetition of this repair process improved overall TON and lifetime ruthenium (II) photocenter, a tetrapyridophenazine (tpphz) bridging ligand and a diiodo-platinum(II) catalytic center (a). Photocatalytic hydrogen production with Ru(tpphz)PtI2 (b, TON = turnover number). Through the short exposure of the hydrogenated PMD to in situ generated singlet oxygen (1O2), the photocatalyst is re-oxidized to its active form and is again applicable for light-driven hydrogen production. By the repetitive active repair of the damaged photocatalyst, the long-term activity of the PMD is prolonged to weeks of active hydrogen formation. Research question
• Why is the catalytic performance of the photocatalyst in consecutive runs getting lower? o Hypothesis – 1O2 attacks the structure of the catalyst leading to oxidative destruction of the ligand units
• HPLC of the supramolecular photocatalyst before photocatalysis, after photocatalysis, after repair for the consecutive repair cycles may lead to the identification of the degradation processes occurring o See hypothetical strucutres, (note Ru-tpphz-PtI2 is chemically, photochemically a very stable molecule)