Nanostructured photoelectrodes for solar water splitting

Roland Marschall^a

^aUniversity of Bayreuth, Weiherstraße, 26, Bayreuth, Germany

Proceedings of MATSUS Fall 2025 Conference (MATSUSFall25)

E.22 Photoelectrochemical approaches for added-value chemicals and waste valorization - #PecVal

València, Spain, 2025 October 20th - 24th

Organizers: Salvador Eslava, Sixto Gimenez Julia and Ana Gutiérrez Blanco

Invited Speaker, Roland Marschall, presentation 035
Publication date: 17th July 2025

Efficient conversion and storage of solar energy are crucial steps in the establishment of a renewable and carbon neutral energy supply. Photoelectrochemical (PEC) water splitting is a promising energy conversion and storage technology, considered very promising to make use of the large amounts of sunlight that reach the surface of earth. It renders the direct conversion of light into chemical energy possible, e.g. solar fuels like hydrogen or ammonia. By the aid of nanostructuring, diffusion pathways can be drastically shortened in case of low charge carrier diffusion lengths.

Due to its high electric conductivity, beneficial hole diffusion length, and band gap of 2.7 eV suitable to absorb visible light, WO₃ is a well-understood photoanode for photoelectrochemical water splitting.[1,2] In this contribution, a study to unravel the influence of seed layers on the performance of hydrothermally-grown WO₃photonanodes will be presented.[3] Moreover, using a sol-gel synthesis method adapted from Hillard et al.,[4] we systematically investigated the influence of calcination temperature, film thickness, and porosity on the structural, optical, and electronic properties of WO₃ thin films, reaching photocurrent exceeding 3 mA cm^-2.

In recent years, earth-abundant Fe-based materials like spinel ferrites have emerged as auspicious materials for PEC. They have the inherent ability to absorb a large part of the visible light spectrum with band gaps around 2 eV, while some of them being also very good electrocatalysts. In this presentation, the activity and stability of both pristine and hydrogen-treated ZnFe₂O₄ will be presented.[5] Using an illuminated scanning flow cell setup, we monitored the activity and dissolution rates of ZnFe₂O₄ under operando PEC conditions. It was found that at PEC water oxidation conditions, ZnFe₂O₄ does not degrade in basic pH. Moreover, thermally reduced ZnFe₂O₄ shows expected higher OER activity without compromising the stability compared to the pristine one.

References:

[1] J. M. Berak, M. J. Sienko, J. Solid State Chem. 1970, 2, 109–133.

[2] Z. F. Huang, J. Song, L. Pan, X. Zhang, L. Wang, J.J. Zou, Adv. Mater. 2015, 27, 5309–5327.

[3] M. Ade, L. Schumacher, R. Marschall, Sustain. Energy Fuels 2023, 7, 4332-4340.

[4] S. Hilliard, G. Baldinozzi, D. Friedrich, S. Kressman, H. Strub, V. Artero, C. Laberty-Robert, Sust. Energy Fuels 2017, 1, 145–153

[5] N. Cheng, L. Kanzler, Y. Jiang, A. Mingers, M. Weiss, C. Scheu, R. Marschall, S. Zhang, ACS Catal. 2024, 14, 10789–10795.

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