The water photo-oxidation reaction mechanism on bare and co-catalyst coated hematite photoanodes for solar water splitting

events hall

Mr. Anton Tsyganok

10.04.2022

David Wang Auditorium, 3rd floor Dalia Meidan Bldg.

14:30

Hematite is an attractive candidate for photoanodes for solar water splitting based on its favorable properties. However, the performance of state-of-the-art hematite photoanodes is still far short of the theoretical efficiency. Some of the efficiency losses result from the water photo-oxidation reaction between the photoanode and the electrolyte. This seminar addresses key questions related to the reaction mechanism on hematite photoanodes with and without a co-catalyst overlayer.

The water photo-oxidation reaction mechanism on bare hematite photoanodes was studied by potentiodynamic discharge measurements following polarization under water photo-oxidation conditions. The metastable surface intermediates discharge in a double-peak wave during cathodic potential sweep. The relative peak heights were found to reverse after long time delays since turning the light off. This observation indicates that the discharge proceeds in parallel pathways, suggesting the same for water photo-oxidation reaction. The suggested parallel reaction mechanism was supported using impedance spectroscopy and a micro-kinetic modeling.

The role of FeNi (oxy)hydroxide overlayer in improving the photoanode performance was studied by operando X-ray absorption spectroscopy measurements. Only the Ni K-edge spectra showed pronounced dependence on potential in dark and under illumination. The results suggest that the photo-generated holes in the hematite layer transfer mainly to the Ni atoms in the overlayer, resulting in reduced electron-hole recombination and cathodic shift in the onset potential.

BIO

Acquired BSc and MSc degrees at Materials Science and Engineering faculty in Technion.
For the master degree studied the effect of FeNi (oxy)hydroxide overlayer for improving hematite photoanodes performance by means of photoelectrochemical impedance spectroscopy (PEIS) and intensity modulated photocurrent spectroscopy (IMPS).

Supervisor: Prof. Avner Rothschild