Based on our previous covalent dye-catalyst assembly for hydrogen evolution in dye-sensitized photoelectrochemical cells (DSPEC)[1], a new dyad was synthesized, introducing an extended linker to improve charge transfer, light harvesting properties and stability in aqueous media.[2] Furthermore, the catalyst unit was changed to a tetraaza-macrocyclic Co catalyst with higher activity[3]. Hydrogen evolution activity of NiO films sensitized with the new dyads was significantly improved.
Transient absorption spectroelectrochemistry (TA-SEC) was used to investigate the light-induced processes that lead to the catalytically active state in the sensitized NiO films under applied potential. Application of a potential allows to study the system under conditions close to the operando conditions in photoelectrochemical tests and in various oxidation states of the catalyst[4]. It has been shown to strongly influence the charge recombination kinetics in sensitized NiO films[5,6].
Charge separation and charge-separated state lifetimes could be determined and showed heavy dependence on the applied potential, increasing by up to six orders of magnitude into the millisecond scale. Furthermore, electron transfer to the catalyst unit to form the long-lived (> 1 ms) catalytically active state was observed, allowing a correlation of light-induced process kinetics with the observed catalytic performance.

[1]: Kaeffer, N., Massin, J., Lebrun, C., Renault, O., Chavarot-Kerlidou, M., & Artero, V., Journal of the American Chemical Society, 2016, 138(38), 12308–12311.
[2]: Click, K. A., Beauchamp, D. R., Huang, Z., Chen, W., & Wu, Y., Journal of the American Chemical Society, 2016, 138(4), 1174–1179.
[3]: Varma, S., Castillo, C. E., Stoll, T., Fortage, J., Blackman, A. G., Molton, F., Deronzier, A., & Collomb, M.-N., Physical Chemistry Chemical Physics, 2013, 15(40), 17544.
[4]: Bold, S., Zedler, L., Zhang, Y., Massin, J., Artero, V., Chavarot-Kerlidou, M., & Dietzek, B., Chemical Communications, 2018, 54(75), 10594–10597.
[5]: Dillon, R. J., Alibabaei, L., Meyer, T. J., & Papanikolas, J. M., ACS Applied Materials & Interfaces, 2017, 9(32), 26786–26796.
[6]: D’Amario, L., Antila, L. J., Pettersson Rimgard, B., Boschloo, G., & Hammarström, L., The Journal of Physical Chemistry Letters, 2015 6(5), 779–783.