(671f) Nanostructured Photoelectrodes for Enhanced Charge Carrier and Mass Transfer in Solar Water Spitting

Photoelectrochemical water splitting for hydrogen production by semiconductors has been extensively investigated in recent decades for the conversion and storage of the intermittent solar energy. During this process, photo-generated charge carriers will transfer from the bulk to the surface of photoelectrodes for the water splitting reaction. Meanwhile, hydrogen and oxygen bubbles formed upon the surface reaction will detach from the surface of photoelectrodes. However, unfavorable surface and interface structures will hinder the transfer of charge carriers, which severely limits the overall efficiency. Additionally, a poor wettability of the electrode will result in the accumulation of hydrogen and oxygen bubbles, which imposes a significant mass transfer resistance between electrolyte and electrode.

This research describes the design and synthesis of nanostructured photoelectrodes for enhanced charge carrier transfer and bubble detachment. Fe₂O₃ nanotubes was synthesized with shortened distance for charge collection, exhibiting a photocurrent density of 1.5 mA/cm2 at 1.23 V vs. RHE. A dendritic nanostructured Fe2O3 photoanode was also obtained for enhanced solid-liquid junction area to improve the charge collection efficiency, generating a photocurrent of ~2.5 mA cm^-2 at 1.23 V vs. RHE. For Si based photoanodes that suffer from interface defects, a high-quality Al₂O₃ tunnelling layer was introduced to repair the interfacial defects and suppress charge recombination, yielding a photocurrent density of ~ 28 mA cm^-2 at 1.23 V vs. RHE for oxygen evolution. Eventually, planar Si(100) substrate was etch to expose the (111) facets, forming micro-pyramid structures. The enhanced wettability of the pyramid structured Si photocathode exhibited a water reduction photocurrent of 35 mA cm^-2 at 0 V vs. RHE, which was caused by the promoted detachment of hydrogen bubbles.