(548b) Transparent ALD-Grown Ta2O5 Protective Layers for Corrosion Vulnerable Photoanodes in Solar Water Splitting

Transparent ALD-grown Ta₂O₅protective layers for corrosion vulnerable photoanodes in
solar water splitting

Tuo Wang*,
Chengcheng Li, Jinglong Gong

Key
Laboratory for Green Chemical Technology of Ministry of Education; School of
Chemical Engineering and Technology, Tianjin University; Collaborative
Innovation Center of Chemical Science and Engineering; Tianjin 300072, China

*E-mail: wangtuo@tju.edu.cn

Photoelectrochemical water splitting for
hydrogen production by semiconductors has been extensively investigated in
recent decades for the conversion and storage of the intermittent solar energy.
However, photocorrosion caused by oxidative holes has restricted the
application of many promising semiconductors (such as ZnO, Si) during the water
oxidation reaction, which is considered particularly demanding compared with
the reduction of protons. Chemically stable protective layers have been
investigated to alleviate this problem, whereas their optical properties are
rarely examined explicitly as a contributing factor. This work describes the
design and fabrication of highly stable corrosion vulnerable photoanodes with
ultrathin (~1.5 nm) Ta₂O₅ protective layers conformally
deposited by atomic layer deposition. The photocurrent of the protected
electrode remains stable during stability tests over several hours without
degradation, while the bare electrode shows a fast decay because of
photocorrosion. The optical property of Ta₂O₅ ensures its
transparency to sunlight, prohibiting the generation of high energy oxidative
holes from
Ta₂O₅
that will attack the underlying material. The stability of protected
electrode is deteriorated upon the incorporation of high energy UV light (¦Ë
< 290 nm) to deliberately generate holes from Ta₂O₅. It is
concluded that the transparency of Ta₂O₅ to sunlight is
the main reason accounting for the excellent stability of the photoanode.
Moreover, the photoactivity of the electrode is improved due to the surface
state passivation effect of Ta₂O₅, and the photocurrent
can be further increased upon the deposition of additional surface catalytic
layers such as NiO. This study may provide a new perspective on selecting
protective materials for unstable semiconductors by evaluating the transparency
of the overlayer.