Publication date: 31st March 2013
The tandem design for harvesting solar light for direct water splitting is an interesting route for future sustainable energy production. In this regard, silicon has been found to be an excellent material for photocathodic H2 evolution. While silicon is stable at the reductive potentials used for H2 evolution, the ease in which Si oxidizes in many other conditions restricts one’s freedom when working with these electrodes. In this work a couple nm of Ti were sputter deposited onto the Si thus protecting the silicon from oxidation while still allowing light to pass through. This allowed for the oxidative electrodeposition of a MoSx catalyst. Upon testing this composite for photocathodic H2 evolution, an electrode was produced with a H2 evolution onset of ~+0.33 V vs. RHE and a Tafel slope of 39mV/decade in red light (lamda >635 nm, 38.6 mW/cm2. After a couple hours of testing it was found that the Ti protective layer was degrading. To resolve this issue a Ti/TiO2 protective layer was investigated. A Pt catalyst was used to focus solely on support stability. Using a Pt/100nm TiO2/5nm Ti/n+p Si electrode an onset of +0.52V vs. RHE and a Tafel slope of 30mV/decade was achieved in red light. This electrode was stable for at least 3 days. Using a Fe(II)/Fe(III) redox couple it was found that the bandbending of TiO2 prevented a large majority of oxidative reactions from occurring. This band bending effect prevented the oxidative electrodeposition of the MoSx catalyst on the TiO2/Si. However in most cases the oxidation of catalyst deactivates them, thus we feel the TiO2’s bandbending properties will typically be a beneficial property for photocathodic H2 evolution.
Cyclic voltammetry of photoelectrocatalytic HER of various n+p-Si electrodes. The samples were irradiated with red light (AM1.5 cut-off <635 nm, 38.6 mW/cm2) and scanned at 50 mV/s.
Seger, B.; Pedersen, T.; Laursen, A. B.; Vesborg, P. C. K.; Hansen, O.; Chorkendorff, I., Using TiO(2) as a Conductive Protective Layer for Photocathodic H(2) Evolution. Journal of the American Chemical Society 2013, 135, 1057-64. Seger, B.; Laursen, A. B.; Vesborg, P. C. K.; Pedersen, T.; Hansen, O.; Dahl, S.; Chorkendorff, I., Hydrogen Production Using a Molybdenum Sulfide Catalyst on a Titanium-Protected n plus p-Silicon Photocathode. Angewandte Chemie-International Edition 2012, 51, 9128-9131. 1. Seger, B.; Pedersen, T.; Laursen, A. B.; Vesborg, P. C. K.; Hansen, O.; Chorkendorff, I., Using TiO(2) as a Conductive Protective Layer for Photocathodic H(2) Evolution. Journal of the American Chemical Society 2013, 135, 1057-64. 2. Seger, B.; Laursen, A. B.; Vesborg, P. C. K.; Pedersen, T.; Hansen, O.; Dahl, S.; Chorkendorff, I., Hydrogen Production Using a Molybdenum Sulfide Catalyst on a Titanium-Protected n plus p-Silicon Photocathode. Angewandte Chemie-International Edition 2012, 51, 9128-9131.
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