Lay summary

Photoelectrochemical cells (PEC) can convert solar energy into clean hydrogen fuel by solar water Splitting. In this SNF project we investigate how metal oxides interact with the electrolyte in PEC cells at the molecular level by using advanced synchrotron x-ray and photoelectron spectroscopy methods.

In PEC anode materials, solar energy creates electron-hole pairs which separate under an external field; the holes diffuse to the anode-electrolyte interface into the electrolyte where they can oxidize water and generate oxygen gas; in return, an electron from the electrolyte enters the anode material, and at the cathode hydrogen is evolved which can be used as fuel.

Defects in the bulk of the electrode materials can cause premature recombination of the electron hole pairs and thus work against the efficiency of PEC electrodes. Hematite, an otherwise quite suitable PEC anode materials, has a very short hole diffusion length with a limited efficiency of the system.

Defects at the electrode surface can be beneficial, however. Our recent operando study of a PEC system under light and bias showed the existence of 2 different types of electron holes during PEC operation.


[1] A. Braun, S. Erat, X. Zhang, Q. Chen, F. Aksoy, R. Löhnert, Z. Liu, S.S. Mao, T. Graule, Surface and bulk oxygen vacancy defect states near the Fermi level in 100 nm WO3-δ/TiO2 (110) films: A resonant valence band photoemission spectroscopy study, J. Phys. Chem. C.


[2] D.K. Bora, A. Braun, S. Erat, R. Löhnert, A.K. Ariffin, R. Manzke, K. Sivula, T. Graule, M. Grätzel, E. Constable, Evolution of an oxygen NEXAFS transition in the upper Hubbard band in α-Fe2O3 upon electrochemical oxidation, J. Phys. Chem. C, 2011, 115 (13), 5619–5625.

http://pubs.acs.org/doi/abs/10.1021/jp108230r   http://arxiv.org/abs/1106.1089

[3] D. Bora, A. Braun, R. Erni, G. Fortunato, T. Graule, E. Constable, Hydrothermal treatment of a hematite film leads to highly oriented faceted nanostructures with enhanced photocurrents, Chem. Mater. 2011, 23, 2051–2061


[4] R. Solarska, A. Heel, J. Ropka, A. Braun, L. Holzer, J. Ye, T. Graule. Enhancement of Photocatalytic Performance of Calcium Bismuth Mixed Oxide by One-Step Flame Spray Synthesis. Applied Catalysis A 2010, 382(2) 190-196.


[5] A. Braun, K.K. Akurati, G. Fortunato, F.A. Reifler, A. Ritter, A.S. Harvey, A. Vital, T. Graule, Nitrogen doping of TiO2 photocatalyst forms a second eg state in the Oxygen (1s) NEXAFS pre-edge, J. Phys. Chem. C, 2010, 114 (1), 516–519

http://pubs.acs.org/doi/pdf/10.1021/jp908875t  http://arxiv.org/abs/1106.1026