Photodegradation of CuBi<sub>2</sub>O<sub>4</sub> Films Evidenced by Fast Formation of Metallic Bi using Operando Surface‐sensitive X‐ray Scattering**
Davide Derelli, Francesco Caddeo, Kilian Frank, Kilian Krötzsch, Patrick Ewerhardt, M. A. von Krüger, Sophie Medicus, Lars Klemeyer, Marvin Skiba, Charlotte Ruhmlieb, Olof Gutowski, Ann‐Christin Dippel, Wolfgang J. Parak, Bert Nickel, Dorota Koziej
Abstract
Abstract CuBi 2 O 4 has recently emerged as a promising photocathode for photo‐electrochemical (PEC) water splitting. However, its fast degradation under operation currently poses a limit to its application. Here, we report a novel method to study operando the semiconductor‐electrolyte interface during PEC operation by surface‐sensitive high‐energy X‐ray scattering. We find that a fast decrease in the generated photocurrents correlates directly with the formation of a metallic Bi phase. We further show that the slower formation of metallic Cu, as well as the dissolution of the electrode in contact with the electrolyte, further affect the CuBi 2 O 4 activity and morphology. Our study provides a comprehensive picture of the degradation mechanisms affecting CuBi 2 O 4 electrodes under operation and poses the methodological basis to investigate the photocorrosion processes affecting a wide range of PEC materials.