Fullerene as a Photoelectron Transfer Promoter Enabling Stable TiO ₂ -Protected Sb ₂ Se ₃ 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.