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Enhanced photopromoted electron transfer over a bilayer WO3 n-n heterojunction prepared by RF diode sputtering


A bilayer WO3 photoelectrode was obtained by radio frequency (RF) plasma sputtering in reactive 40%O2/Ar atmosphere by depositing on a tungsten foil two successive WO3 coatings at two different total gas pressures (3 Pa and 1.7 Pa, respectively), followed by calcination at 600 °C. Two monolayer samples deposited at each of the two pressures and a bilayer sample deposited at inverted pressures were also prepared. Their photoelectrocatalytic (PEC) activity was evaluated by both Incident Photon-to-Current Efficiency (IPCE) measurements and separate evolution of H2 and O2 by water splitting in a two-compartment PEC cell. SEM analysis revealed that the photoanodes have a nanostructured porous double layer surmounting a columnar basement (Staffa-like morphology, after the name of the Scottish island). Mott-Schottky analysis showed that the single layer deposited at 3 Pa has a conduction flat band potential 0.1 V more positive than that deposited at 1.7 Pa. The equivalent n-n heterojunction at the interface of the double-layer creates a built-in electric field that facilitates the photopromoted electron transfer toward the lower laying conduction band material, while the columnar innermost layer introduces percolation paths for efficient electron transport toward the conductive tungsten foil. Both phenomena contribute to decrease the interfacial charge transfer resistance (Rct) and lead up to a ca. 30% increase in the PEC performance compared to the monolayer and to the inverted bilayer coatings and to a 93% faradaic efficiency, which is among the highest reported so far for WO3 photoanodes. Upon methanol addition an outstanding 4-fold photocurrent density increase up to 6.3 mA cm-2 was attained over the bilayer WO3 photoanode, much larger than the usually observed current doubling effect.

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Publication details

The article was accepted on 18 May 2017 and first published on 18 May 2017

Article type: Paper
DOI: 10.1039/C7TA03887A
Citation: J. Mater. Chem. A, 2017, Accepted Manuscript
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    Enhanced photopromoted electron transfer over a bilayer WO3 n-n heterojunction prepared by RF diode sputtering

    G. L. Chiarello, M. Bernareggi, M. Pedroni, M. Magni, S. Pietralunga, A. Tagliaferri, E. VASSALLO and E. Selli, J. Mater. Chem. A, 2017, Accepted Manuscript , DOI: 10.1039/C7TA03887A

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