In Situ Photocorrosion Assessment of Protected Hematite Photoanodes During Accelerated Stress Tests

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

Congreso; 34th Topical Meeting of the ISE; 2023

Photoelectrochemical (PEC) water splitting produces H2 from sunlight and water, enabling the green storage of solar energy. The lifetime of the employed metal oxide photoanodes is limited by the photo-corrosion of the semiconductor materials, where the active dissolution of metals during the PEC oxygen evolution reaction (OER) has shown to play a significant role in the degradation [1]. To extend the lifetime of the photoanodes, the deposition of protective overlayers has been intensively researched [2,3]. For improving PEC cells even further, fundamental research on the stability using in situ techniques is indispensable to determine the best protection strategy that enhances long-term performance. In this work, we prepared Fe2O3 nanorods as a model system and modified the surface with ultrathin TiO2 overlayers using atomic layer deposition (ALD). The influence of overlayer thickness and annealing treatment after the ALD is evaluated regarding the PEC activity and stability in alkaline electrolyte. Particularly, we propose using an accelerated stress test (AST) to obtain more representative information on the long-term performance of the photoanodes in a shorter time scale. The AST protocol consisted of 3 s potentiostatic pulses alternating between open circuit potential (OCP) and 1.7 VRHE. To quantify the stability and activity, 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) HR-TEM of TiO2@Fe2O3 b) Photocurrent of the different modified photoanodes at 1.5 VRHE in NaOH 50 mM. c) Typical stability measurement during an AST. Top tile: obtained current density under irradiation, bottom tile: Resulting Fe dissolution in NaOH 50 mM. Figure 1a shows that the ALD allowed depositing a conformal and continuous TiO2 overlayer on the Fe2O3. Figure 1b indicates that the increase in thickness hinders the obtained photocurrent while a short annealing step increases the activity. Figure 1c shows that the dissolution of Fe is significantly decreased with the TiO2 overlayer, and the activity is better retained during an AST. Therefore, selecting appropriate thickness and annealing conditions can prevent the dissolution during PEC conditions and mitigate the performance loss during an AST.