Low-Cost Nanomaterials for Photoelectrochemical Water Splitting - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 281

Fig. 13 Photoelectrochemical performance of the unmodified hematite photoanode and the same
anode modified with IrO 2 nanoparticles under AM 1.5G 100 mW/cm 2 simulated sunlight. The
dashed line is the photocurrent for the former state-of-the-art hematite photoanode. Reproduced
with permission from [ 90 ]
3.4 Other Low-Cost Nanomaterials for PEC Water
Oxidation
In addition to these binary metal oxides, ternary metal oxides such as SrTiO 3 [ 67 ,
117 ] and BiVO 4 [ 113 - 115 , 121 ] have also been studied for PEC water oxidation.
Ternary metal oxides could provide new opportunities in developing photoelec-
trode, as their electronic bands are formed by atomic orbitals from more than one
element and the modulation of the stoichiometric ratio of the elements could finely
tune the potentials of valence and conduction bands as well as the band-gap energy
[ 95 ]. SrTiO 3 has favorable band-edge positions that straddled the water oxidation
and reduction potentials. However, the large band-gap SrTiO 3 (3.75 eV) limits its
efficiency for water oxidation. Zhang et al. used a hydrothermal method to fabricate
SrTiO 3 nanocrystals modified TiO 2 nanotube arrays for PEC water splitting [ 117 ].
They found that the incorporation of SrTiO 3 could shift the flat band potential of
TiO 2 to a more negative value, and thus, improve its PEC performance. BiVO 4 has a
favorable band-gap of 2.3 eV for efficient absorption of solar light. Furthermore, its
conduction band is close to 0 V versus RHE at pH = 0, as a result of the overlap of
empty Bi 6p orbitals with anti-bonding V 3d-O 2p states, which can reduce the need
for external bias for PEC water splitting. However, charge transport and interfacial
charge transfer have been found to be key limiting factors for PEC water splitting. A
number of methods have been demonstrated to improve their charge transport
efficiency and further improve their PEC performance. For example, Mo- and W-
doped BiVO 4 have been demonstrated to increase the solar energy conversion
efficiency for PEC water splitting by improving their carrier densities with W and