The
search for clean fuel sources has been driven by a rising energy demand and
increasing awareness of anthropogenic climate change. One attractive strategy
is the storage of solar energy in the bonds of H2 and O2 by
photoelectrolysis, or photoelectrochemical water splitting. Hematite (α-Fe2O3)
has emerged as a promising photoanode material for solar-driven water splitting
due to its relative abundance, non-toxicity, chemical robustness, and suitable
bandgap (~2.1 eV), which corresponds to a maximum solar-to-hydrogen efficienc
of 15%. However, its performance to date has been limited primarily by poor
charge transport properties and sluggish oxygen evolution reaction kinetics.
These limitations can be overcome with combined efforts in nanostructuring and surface
catalysis. Hematite nanorods were grown on fluorine-doped tin oxide substrates
via chemical bath deposition, a low cost, facile synthesis method. A TiO2
interlayer showed greatly improved conductivity in the nanorods due to
diffusion of Ti into the α-Fe2O3 lattice. Nanorods with
catalyst overlayers of Sn, Nb, and Co-Pi demonstrated better performance as a
result of reduced surface limitations. The roles of annealing, bulk dopants,
and catalysts were characterized by Mott-Schottky analysis, electrochemical
impedance spectroscopy, and photoelectrolysis. The photoanodes developed compare
favorably with state-of-the-art, especially considering the extreme ease of
synthesis methods used herein.
