posted on 2024-03-07, 17:39authored byKathleen Becker, Chengcan Xiao, Samutr Assavachin, Anna Kundmann, Frank E. Osterloh
Gallium phosphide is an established photoelectrode material
for
H2 or O2 evolution from water, but particle-based
GaP photocatalysts for H2 evolution are very rare. To understand
the reasons, we investigated the photocatalytic H2 evolution
reaction (HER) of suspended n-type GaP particles with iodide, sulfite,
ferricyanide, ferrous ion, and hydrosulfide as sacrificial electron
donors, and using Pt, RhyCr2–yO3, and Ni2P HER cocatalysts.
A record apparent quantum efficiency of 14.8% at 525 nm was achieved
after removing gallium and oxide charge trapping states from the GaP
surface, adding a Ni2P cocatalyst to reduce the proton
reduction overpotential, lowering the Schottky-barrier at the GaP–cocatalyst
interface, adjusting the polarity of the depletion layer at the GaP–liquid
interface, and optimizing the electrochemical potential of the electron
donor. The work not only showcases the main factors that control charge
separation in suspended photocatalysts, but it also explains why most
known HER photocatalysts in the literature are based on n-type and
not p-type semiconductors.