Role of TiO 2 coating layer on the performance of Cu 2 O photocathode in photoelectrochemical CO 2 reduction

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Abstract
TiO 2 is usually employed as a protective layer for Cu 2 O in photoelectrocatalytic CO 2 reduction. However, the role of TiO 2 layer on CO 2 reduction activity and selectivity is still elusive. In this work, a systematic investigation is carried out to probe the impact of the deposition parameters of TiO 2 overlayer, including the temperature and thickness, on CO 2 reduction performance. Compositional and (photo-)electrochemical analysis is performed to explore the property of TiO 2 overlayers. Carrier behavior, including donor density and electron energy, and stability of TiO 2 are demonstrated to be influenced by atomic layer deposition conditions and thus play a role in controlling CO 2 reduction reaction. Specifically, as the thickness of the TiO 2 layer increases from 2 to 50 nm, the electron energy tends to be lowered accompanying the electron transfer mode from tunneling for TiO 2 thin layers to type II for thick TiO 2 , leading to a decrease in CO 2 reduction selectivity. With an increase of the TiO 2 deposition temperature, the stability increases with a loss of conductivity. Cu 2 O coated with 2 nm TiO 2 at 150 °C is proven to be the optimized candidate in this work for photoelectrochemical reduction of CO 2 to CO, HCOOH and CH 3 COOH under an applied bias of −0.4 versus RHE.
Funding Information
  • National Natural Science Foundation of China (21673052)
  • Strategic Priority Research Program of Chinese Academy of Sciences (XDB36000000)
  • Belt and Road Initiative by Chinese Adacemy of Sciences (121D11KYSB20170050)

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