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2014 MRS Spring Meeting


D9.04 - Efficient Water-Splitting BiVO Photoanode Deposited with Reactive Sputtering Method


Apr 25, 2014 9:00am ‐ Apr 25, 2014 9:15am

Description

Water splitting using sun light is a promising strategy to harvest abundant solar energy on the Earth. BiVO has appeared as an important semiconducting oxide to split water using sun light, because of its appropriate band gap matching with solar spectrum and stability in aqueous solutions under illumination. Among a variety of preparing techniques, including spray pyrolysis and spin-coating, reactive sputtering is proved to be most reliable as a result of commercially available and scalable deposition in modern industry compared with chemical methods.Herein we used reactive sputtering method to deposit highly photoactive bismuth vanadate (BiVO) photoanode. We investigated the effects of V/Bi ratio, deposition and annealing temperatures, molybdenum doping, cobalt phosphate (Co-Pi) catalyst, and wide-bandgap oxide hole-blocking layer on the crystallography and photoelectrochemical properties of BiVO thin films. The results showed that at vanadium rich side and elevated deposition temperature it was prone to form pure-phase monoclinic BiVO, which is more photoactive than tetragonal phase. Although the photocurrent was improved with increased deposition temperature, the situation was not the case after annealing in air for 2 hours at 500°C. Molybdenum dopant can greatly improve the conductivity of electrons. So after doping, the photocurrent could be increased by 3 times, reaching ~1mA/cm. Co-Pi catalyst is proved to be an efficient oxygen evolution catalyst, which can decrease the overpotential of water oxidation. The gate voltage of water oxidation shifted to a much lower value after Co-Pi deposition using electrochemical/photo-assisted electrochemical deposition method. Bulk recombination within photoanode side should also be suppressed to output electrons efficiently. Wider-bandgap tin oxide and tungsten oxide were adopted as hole-blocking layers to reflect holes diffused to the interface. After optimization of experimental conditions including film thickness, we can acquire BiVO photoanode with photocurrent density exceeding 1.8mA/cm at potential 1.23V vs RHE under AM1.5.-------------------------------------------------------------------------Mail address: Hahn-Meitner-Platz 1, 14109, Berlin, GermanyCorresponding author’s email: ellmer@helmholtz-berlin.de

Speaker(s):

  • Klaus Ellmer, Helmholtz-Zentrum Berlin für Materialien und Energie

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