Activation
of Hematite Photoanodes for Solar Water
Splitting: Effect of FTO Deformation
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Abstract
The
sintering at 800 °C is found to induce the diffusion of
Sn from the F-doped SnO<sub>2</sub> (FTO) into the hematite lattice,
enhancing the photoelectrochemical cell (PEC) properties of the hematite
photoanodes, but this diffusion also has detrimental effects on the
conductivity of the FTO substrate. In the present research we examined
the role of FTO deformation during the activation of hematite photoanodes
synthesized on FTO substrates. The incorporation of Sn dopants from
the FTO substrates in the hematite lattice was confirmed by X-ray
photoelectron spectroscopy and was found to increase with sintering
time. Further from the extended X-ray absorption fine structure analysis,
it was found that the diffused Sn atoms affected the metal sites of
the hematite lattice. Increased diffusion of Sn into the hematite
lattice caused structural disordering of the FTO, but optimum sintering
time compensated for the structural disordering and improved the ordering.
Under high-temperature annealing at 800 °C, the FTO substrates
underwent a stoichiometric change that directly affected their electrical
conductivity; their resistivity was doubled after 20 min of sintering.
Activation of hematite photoanodes by high-temperature sintering entails
a kinetic competition between Sn dopant diffusion from the FTO substrate
into the hematite and the resulting thermal deformation and conductivity
loss in the FTO substrates