(436a) Hydrogen Production From Water

Silicon-based photocathodes show promising potential for photoelectrochemical (PEC) water splitting for renewable production of hydrogen.  Trade-offs between stability and efficiency have limited the success of Si-based photoelectrodes.  To overcome this issue, we utilize a thin layer (≈ 2 nm) of strontium titanate, SrTiO₃ (STO), which is grown epitaxially on p-doped Si (001) by molecular beam epitaxy.  The STO layer greatly enhances the stability of the Si-based photocathode.  In addition, the high quality STO layer and clean, low defect interface between STO(001) and Si(001) provides minimal trap states for charge carriers.  Moreover, there is no conduction band offset between STO and Si.  This allows the photo-generated electrons to easily move from the Si substrate to the STO surface, where hydrogen ions are reduced to form gaseous hydrogen.  Based on our electrochemical measurements, we find that the STO-Si photocathode is both stable and exhibits high conversion efficiency.  Studies with continuous Ti/Pt films for H₂ evolution yield a current density above 15 mA/cm²; patterned metal layers are expected to give higher current densities.  The results indicate that Si-based photocathodes for PEC water splitting can be improved using a thin STO layer, providing a viable method for clean hydrogen production.