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

Nanostructured α‐hematite (Fe 2 O 3 ) is a widely studied material for photoanode applications, particularly for driving the oxygen evolution reaction (OER) under visible light irradiation in photoelectrochemical (PEC) cells. Our recent work has shown that Fe 2 O 3 suffers from photocorrosion in alkaline and neutral electrolytes, with a noticeable decline in performance after 5 h of operation. This highlights the need for strategies that enhance the stability of Fe 2 O 3 ‐based photoanodes. To enhance the stability of Fe 2 O 3 nanorods (NR), we employed atomic layer deposition (ALD) to coat the NR with a well‐defined, controlled TiO 2 overlayer designed to protect the photoanode from photocorrosion during PEC operation. The influence of overlayer thickness is evaluated regarding the PEC activity, stability, and photocurrent retention in alkaline electrolyte using a PEC scanning flow cell coupled to an inductively coupled plasma mass spectrometer (PEC‐ICP‐MS). This setup can quantify metal dissolution during PEC OER, allowing the characterization of the photo‐degradation under realistic illumination conditions. An accelerated stress test (AST) protocol was designed to drive degradation faster and obtain insightful information about the stability of the TiO 2 @Fe 2 O 3 heterostructures using in situ PEC‐ICP‐MS. PEC‐ICP‐MS measurements demonstrate that the TiO 2 coating significantly enhances the photocorrosion resistance of Fe 2 O 3 NR in alkaline electrolytes during operation. A TiO 2 thickness of 2.8 nm (50 ALD cycles) offered the most favorable compromise between activity, photocurrent retention, and decrease of Fe dissolution. The proposed methodology combines in situ stability quantification and ASTs as a powerful tool to advance material development and can be extended to other protected photoanodes.