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Aqueous photocurrent measurements correlated to ultrafast electron transfer dynamics at ruthenium tris diimine-sensitized NiO photocathodes

Queyriaux, Nicolas; Wahyuono, Ruri Agung; Fize, Jennifer; Gablin, Corinne; Wächtler, Maria; Martinez, Eugenie; Leonard, Didier; Dietzek, Benjamin; Artero, Vincent; Chavarot-Kerlidou, Murielle
in: Journal of Physical Chemistry C (2017) 5891

Understanding the structural and electronic factors governing the efficiency of dye-sensitized NiO photocathodes is essential to optimize solar fuel production in photo electrochemical cells (PECs). For these purpose, three different ruthenium dyes, bearing either two or four methyl phosphonate anchoring groups and either a bipyridine or a dipyridophenazine ancillary ligand, were synthesized and grafted onto NiO films. These photo electrodes were fully characterized by XPS, ToF-SIMS, UV-vis absorption, time-resolved emission and femtosecond transient absorption spectroscopies. Increasing the number of anchoring groups from two to four proved beneficial for the grafting efficiency. No significant modification of the electronic properties compared to the parent photosensitizer was observed, in accordance with the non-conjugated nature of the grafted linker. The photoelectron chemical activity of the dye-sensitized NiO electrodes was assessed in fully aqueous medium in the presence of an irreversible electron acceptor and photocurrents reaching 190 A.cm-2 were recorded. The transient absorption study revealed the presence of two charge recombination pathways for each of the sensitizers and evidenced a stabilized charge separated state in the dppz derivative, supporting its superior photoelectron chemical activity.

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