Enhancing the Long-Term Photoelectrochemical Performance of TiO₂/Si Photocathodes by Coating of Ti-Doped Mesoporous Hematite

Hematite has been demonstrated as a promising surface cocatalyst for photoelectrochemical cathodes in a strong alkaline electrolyte. However, the reliability of hematite-sensitized photocathodes is still inadequate even with an extra TiO2 passivation layer. Titanium (Ti) doping is shown to significantly enhance the conductivity of hematite. Herein, ordered mesoporous Ti-doped hematite was presynthesized and coated on the surface of TiO2-protected silicon. The obtained composite exhibited greatly improved photoelectrochemical (PEC) performance, where continuous hydrogen production with ∼12 mA cm–2 at 0 V versus a reversible hydrogen electrode for over a week (168 h) with only 5% photocurrent decay in 1.0 M KOH solution was achieved, more than an order of magnitude enhancement in lifetime relative to the pristine hematite. The surface potential investigation suggested a more uniform dispersion of photoelectrons on the surface through Ti doping in hematite particles. The low electronic concentration in the TiO2 layer avoided the self-reduction of TiO2, prolonging the lifetime of the device. This study develops an effective protection mechanism for composite photoelectrodes, providing a promising strategy to protect the photocathode via surface decoration of meticulously tailored catalysts.