Hybrid island-and-sea approach for corrosion protection of Si photocathode in neutral-pH water splitting.

Photoelectrochemical (PEC) water splitting is a promising way for converting solar energy into green hydrogen, yet the long-term stability of the studied photoelectrodes remains a main challenge. Therefore, corrosion protection of photocathode and photoanode materials has attracted attention. Here, we demonstrate a simple yet effective "island-and-sea" strategy to enhance the stability of silicon-based photocathodes in neutral media water splitting. Platinum nanoparticles ("islands") deposited on Si facilitate efficient charge transfer, whereas the remaining surface is passivated with a hydrophobic 1-octadecyl (OD) self-assembled monolayer ("sea") that acts as a corrosion-resistant barrier. This organic-protective layer allows stable PEC operation without altering the semiconductor's band structure and complex fabrication steps. The Si/Pt + OD structure maintains a stable photocurrent over 6 h, compared to a 50% decline after 3 h of operation for the unprotected Si/Pt photocathode. Since neutral electrolytes like seawater are readily available and inexpensive natural resources on the planet, the "island-and-sea" approach applicable for stable operation at neutral pH becomes crucial for real-world applications.