Fullerene as a Photoelectron Transfer Promoter Enabling Stable TiO₂‐Protected Sb₂Se₃ Photocathodes for Photo‐Electrochemical Water Splitting

Understanding the degradation mechanisms of photoelectrodes and improving their stability are essential for fully realizing solar‐to‐hydrogen conversion via photo‐electrochemical (PEC) devices. Although amorphous TiO 2 layers have been widely employed as a protective layer on top of p‐type semiconductors to implement durable photocathodes, gradual photocurrent degradation is still unavoidable. This study elucidates the photocurrent degradation mechanisms of TiO 2 ‐protected Sb 2 Se 3 photocathodes and proposes a novel interface‐modification methodology in which fullerene (C 60 ) is introduced as a photoelectron transfer promoter for significantly enhancing long‐term stability. It is demonstrated that the accumulation of photogenerated electrons at the surface of the TiO 2 layer induces the reductive dissolution of TiO 2 , accompanied by photocurrent degradation. In addition, the insertion of the C 60 photoelectron transfer promoter at the Pt/TiO 2 interface facilitates the rapid transfer of photogenerated electrons out of the TiO 2 layer, thereby yielding enhanced stability. The Pt/C 60 /TiO 2 /Sb 2 Se 3 device exhibits a high photocurrent density of 17 mA cm −2 and outstanding stability over 10 h of operation, representing the best PEC performance and long‐term stability compared with previously reported Sb 2 Se 3 ‐based photocathodes. This research not only provides in‐depth understanding of the degradation mechanisms of TiO 2 ‐protected photocathodes, but also suggests a new direction to achieve durable photocathodes for photo‐electrochemical water splitting.