Improved current collection in WO₃:Mo/WO₃ bilayer photoelectrodes

Abstract

We report on the incorporation of molybdenum into tungsten oxide by co-sputtering and its effect on solar-powered photoelectrochemical (PEC) water splitting. Our study shows that Mo incorporation in the bulk of the film (WO 3 :Mo) results in poor PEC performance when compared with pure WO 3 , most likely due to defects that trap photo-generated charge carriers. However, when a WO 3 :Mo/WO 3 bilayer electrode is used, a 20% increase of the photocurrent density at 1.6 V versus saturated calomel reference electrode is observed compared with pure WO 3 . Morphological and microstructural analysis of the WO 3 :Mo/WO 3 bilayer structure reveals that it is formed by coherent growth of the WO 3 :Mo top layer on the WO 3 bottom layer. This effect allows an optimization of the electronic surface structure of the electrode while maintaining good crystallographic properties in the bulk.

Between photocatalysis and photosynthesis: Synchrotron spectroscopy methods on molecules and materials for solar hydrogen generation

“…We have substituted WO 3 to 5% with various cations (including 5% Mo) and found in no single case an increased photocurrent [27]. Interestingly, if the tungsten oxide is not bulk doped, but coated with a thin Mo-oxide film on top of the WO 3 , then an increased photocurrent was measured [28]. According to the authors, coherent growth of the Mo oxide on the WO 3 allows optimization of the electronic surface structure of the electrode while maintaining good crystallographic properties in the bulk.…”

Mo incorporation in WO3 thin film photoanodes: Tailoring the electronic structure for photoelectrochemical hydrogen production

“…7 Contrary to other reports, 8 resulting WO 3 : Mo photoanodes produced less photocurrent than pure ͑Mo-free͒ WO 3 electrodes. 7 We found that the Mo incorporation had no pronounced impact on the band gap but negatively affected the ͑micro͒structural properties of the photoanode material. 7 To circumvent the latter, we introduced a WO 3 :Mo/ WO 3 bilayer electrode, which showed a ϳ20% photocurrent improvement compared to WO 3 single layers.…”

“…To tailor the optical properties of the WO 3 photoanode, we have thus incorporated Mo. 7 Contrary to other reports, 8 resulting WO 3 : Mo photoanodes produced less photocurrent than pure ͑Mo-free͒ WO 3 electrodes. 7 We found that the Mo incorporation had no pronounced impact on the band gap but negatively affected the ͑micro͒structural properties of the photoanode material.…”

Solar fuel production: Strategies and new opportunities with nanostructures

“…However, the WO 3 :Mo/WO 3 homojunction with a good interface and type II band alignment provided a 20% increase of the photocurrent density at 1.6 V vs. SCE (saturated calomel reference electrode) as opposed to pure WO 3 , because a built-in potential was created at the WO 3 :Mo/WO 3 homojunction, as illustrated in Fig. 5 [52,53]. Building internal fields through the introduction of p/nand homo-junctions buried in a semiconductor through doping control is a classic approach for the construction of electronic devices and solar cells.…”

“…(b) Band alignment of WO 3 :Mo/WO 3 homojunctions. (c) Photocurrent density of WO 3 , WO 3 :Mo, WO 3 :Mo/WO 3 under illumination[52,53].…”