In Situ Lab‐on‐Fiber Platform: A Versatile Tool for Dual‐Mode Optoelectronic Tracking Photocorrosion Dynamics of Cadmium Sulfide

ABSTRACT As versatile catalysts, metal sulfides (MSs) unlock new possibilities for photocatalysis and electrocatalysis, driving innovations in clean energy production. However, they are prone to photocorrosion under illumination, which severely impairs their catalytic efficiency and recyclability, thus fundamentally compromising the stability of the catalytic reaction system. Therefore, critical to this effort is the elucidation of photocorrosion for the practical application of high‐performance catalysts and long‐lasting reactors. Herein, a lab‐on‐fiber sensing platform is developed for in situ, real‐time monitoring of the photocorrosion of cadmium sulfide (CdS). Anchored by a tapered seven‐core optical fiber, the platform facilitates dual‐mode sensing by correlating transmission spectrum evolution with photocurrent dynamics, revealing that CdS photocorrosion exhibits a nonlinear dependence on light intensity. The photocorrosion rate is minimized at 0.8 mW∙cm −2 UV light and is further suppressed by applying a 0.4 V bias. Furthermore, the platform uncovers a protective, dynamic sulfur cycle enabled by sacrificial agents on the catalyst surface. Crucially, key structure–activity relationships of the CdS undergoing photocorrosion are established, enabling the optimization of catalysts and reactors. Beyond catalytic systems, the platform is applicable to the operando exploration of interfacial dynamic behaviors and mechanisms in various nanomaterials, thereby underpinning the design of micro‐nano material interfaces and reaction systems.