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

Abstract 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.