On the Photocorrosion of Hematite Photoanodes: Effect of pH, Electrolyte and Protective Overlayers

BENAVENTE LLORENTE, VICTORIA; KEN J. JENEWEIN; ANDRÉ HOFER; ATTILA KORMÁNYOS; JULIEN BACHMANN; SERHIY CHEREVKO

Congreso; ISE Regional Meeting in Prague; 2022

International Society of Electrochemistry

Photoelectrochemical (PEC) cells are promising energy conversion devices allowing to store solar energy directly in high-energy-density fuels. One of the longstanding challenges in this area is to find stable semiconductor materials for the photoanodes to perform the oxygen evolution reaction (OER) [1]. Recent reports have described photo-degradation pathways involving the dissolution of metals from BiVO4 and WO3 photoanodes [2,3], exposing the importance of an accurate stability assessment of photoanodes during PEC OER. The main goal of this work is to study the stability of photoanodes based on abundant metal oxides absorbing light in the visible range using α-Fe2O3 nanorods as a model system. The influence of pH and electrolyte type on stability is evaluated. Furthermore, protective overlayers are deposited onto α-Fe2O3 nanorods, including stable semiconductor oxides deposited by atomic layer deposition (TiO2) or co-catalysts electrodeposited onto photoanodes (cobalt phosphate). To quantify the stability, an optimized photoelectrochemical scanning flow cell (PEC-SFC) coupled to an inductively coupled plasma mass spectrometer (ICP-MS) was used to detect metal dissolution during PEC OER. This setup includes a solar simulator and AM 1.5 G filter allowing the characterization of the photo-degradation under realistic illumination conditions [4]. Fig.1. A) Scheme of the PEC-ICP-MS setup [4]. B) Top layer: Potentiostatic protocol vs. time also displaying illumination period (yellow area), middle layer: resulting current density, bottom layer: Resulting Fe dissolution in different electrolytes. Figure 1B displays a typical stability measurement of α-Fe2O3 nanorods using alkaline electrolytes under irradiation. The dissolution of Fe species is detected, indicating photo-corrosion of the α-Fe2O3 nanorods. On the other hand, when the alkaline electrolyte contains phosphate salts, a remarkable decrease in Fe dissolution is observed. Therefore, selecting an appropriate electrolyte might alleviate the degradation pathway associated with photo-corrosion of α-Fe2O3 nanorods. The analysis of dissolution phenomena during PEC OER can provide a deeper understanding of the key factors driving the photo-degradation of metal oxide photoanodes. The exploration of surface-modified α-Fe2O3 photoanodes might guide the design of more stable photoactive materials for PEC solar-to-fuel production.