A Facile Electrochemical Reduction Method for Improving Photocatalytic Performance of α-Fe₂O₃ Photoanode for Solar Water Splitting

Electrochemical reduction method is used for the first time to significantly improve the photo-electrochemical performance of α-Fe 2 O 3 photoanode prepared on fluorine-doped tin oxide substrates by spin-coating aqueous solution of Fe(NO 3 ) 3 followed by thermal annealing in air. Photocurrent density of α-Fe 2 O 3 thin film photoanode can be enhanced 25 times by partially reducing the oxide film to form more conductive Fe 3 O 4 (magnetite). Fe 3 O 4 helps facilitate efficient charge transport and collection from the top α-Fe 2 O 3 layer upon light absorption and charge separation to yield enhanced photocurrent density. The optimal enhancement can be obtained for <50 nm films because of the short charge transport distance for the α-Fe 2 O 3 layer. Thick α-Fe 2 O 3 films require more charge and overpotential than thinner films to achieve limited enhancement because of the sluggish charge transport over a longer distance to oxidize water. Electrochemical reduction of α-Fe 2 O 3 in unbuffered pH-neutral solution yields much higher but unstable photocurrent enhancement because of the increase in local pH value accompanied by proton reduction at a hematite surface.