Mechanism Investigation of the Postnecking Treatment to WO3 Photoelectrodes

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