Suitable photo-electrode materials are known to be the main bottleneck for large scale deployment of devices for solar fuel production. These semiconducting materials must be efficient, stable and scalable, although, usually two out three of these qualities are met. Hematite is an extensively researched photoelectrode material, known for its long-lasting properties and facile synthesis. However, the position of its band edges and high recombination rates, resulting in low efficiencies, preclude hematite to be used in real applications. On the other hand, complex photo-electrodes with laborious synthesis, e.g. III-V tandems absorbers (GaInP/GaAs), coupled with RuO_x and PtRu catalysts, have proven to be highly efficient for water splitting [1].

With the aim to improve scalability, concentrated light sources allow the use of smaller photoelectrodes, provided they are stable and efficient at operating conditions. However, the use of higher irradiation (>100 kW m^-2) unlocks additional constraints related to heat management, ohmic drop due to inordinate current densities, and unknown electron/hole transfer kinetics under high photon flux and at higher temperatures. It is expected that these effects could be alleviated by careful reactor design, and choosing suitable substrates and operating conditions. However, these issues have been seldom investigated and only a few studies on photoelectrochemical cells for irradiations typically below 30 suns have been reported [2].

Here, we present the model and preliminary experimental validation of a photo-electrochemical cell operating under concentrated irradiation (>100 kW m^-2), using metal oxides (Fe₂O₃ and BiVO₄) as photoelectrode materials, which were selected due to their well-known and predictable photoelectrochemical behavior [3,4]. The effects of the substrate material (Ti or transparent conductive oxides deposited on glass), electrode configuration, electrolyte flow and spectrally resolved photon intensities on the performance of the cell will be presented. Initial predictions indicate that conductive glass is not a suitable substrate due to its low thermal conductivity, resulting in undesirable high temperatures (>80 °C) when operating under irradiations of 600 kW m^-2.

References:

[1] Young, J., Steiner, M., Döscher, H. et al. Nat Energy 2017, 2, 17028.

[2] Vilanova, Mendes, A. Journal of Power Sources 2020, 454, 227890.

[3] Bedoya-Lora, F. Hankin, A. Kelsall, G. J. Mater. Chem. A, 2017, 5, 22683-22696

[4] Gaudy, Y. Haussener, S. et al. J. Mater. Chem. A, 2018, 6, 17337-17352