Nanoporous WO3 photoanodes are prepared by an electrophoretic
deposition method. Postnecking treatment of the WO3 photoanodes
by dropping ammonium metatungstate solution following annealing remarkably
improves the photocurrent of photoelectrochemcial (PEC) water oxidation.
Water oxidation photocurrent density is promoted by a factor of 16
at 1.23 VRHE. To disclose the mechanism for the improvement,
corresponding samples are prepared and investigated by scanning electron
microscopy, electrochemical impedance spectroscopy, and PEC measurement
both in Na2SO4 and Na2SO3 electrolyte. It is found that the significantly increased photocurrent
is mainly due to improved electron transport rather than suppressed
back-reaction at the FTO surface, passivating surface states, or other
reasons. With introduction of a compact layer by pretreating FTO with
ammonium metatungstate, the photocurrent of the necking-treated WO3 photoanode can be further improved, via suppressing the back-reaction
at FTO surface. Both strategies of improving charge transport and
suppressing the back-reaction at the FTO surface can offer a reference
to enhance the photocurrent for other porous photoelectrodes.
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