The effect of CO₂ and H₂O molecule adsorption on SCN-Black TiO₂ during photocatalytic CO₂ reduction

Fang-Yu Fu^1,2*, Tsai-Yu Lin², Chiu-Ching Liao², Putikam Raghunath⁴, Ming-Chang Lin⁴, Chih-I Wu¹, Kuei-Hsien Chen³, Li-Chyong Chen^2,5, Heng-Liang Wu^2,5

¹Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan
²Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
³Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
⁴Department of Applied Chemistry, National Chiao Tung University, Hsinchu, Taiwan
⁵Center of Atomic Initiative for New Materials, National Taiwan University, Taipei, Taiwan

* Presenter:Fang-Yu Fu, email:Fangyufu0601@gmail.com

The gas molecule adsorbs on semiconductor surface will dramatically influence the semiconductor charge transport kinetics, desorption amount of gas molecule and the performance of photochemical reaction. From CO₂ reduction reaction, typically CO₂ gas pass through water container then act as reaction gas, the mixture gas caused the problem to identify whether initial CO₂ or H₂O molecule adsorption behavior will further influence CO₂ reduction reaction performance or not.

Based on our previous study, the KSCN-modified hydrogenated nickel nano-cluster-modified black TiO₂ (SCN-B-TiO₂) exhibits enhanced photocatalytic CO₂ reduction due to the interfacial dipole effect [1]. In order to investigate the effect of CO₂ and H₂O molecule during photocatalytic CO₂ reduction reaction, we perform the sequential purge CO₂ and H₂O gas molecule on SCN-B-TiO₂ surface and not only study the CO₂ reduction activity, also conduct in-situ FTIR, in-situ UPS analysis with different sequence CO₂ and H₂O molecule adsorption condition, to construct relationship between initial stage of surface functional groups, band structure and final results of photocatalytic performance.

Our results exhibited that CO₂ gas come initial stage (CO₂ first) is similar with mixture gas, however the H₂O first dramatically suppress the SCN-B-TiO₂ sample catalytic activity, and in-situ FTIR analysis shows the CO₂ first have form less carbonate species and with light irradiation shows faster desorption amount of CO₂ radical, in-situ UPS analysis shows CO₂ first adsorb on SCN-B-TiO₂ will have downward shift 0.2 eV of band structure, however H₂O we did not observe clear shift, this downward band bending behavior which would enhance interfacial charge transport kinetics. The in-situ UPS results have further confirmed through computational DOS analysis.

[1] F. Y. Fu, ACS Applied Material Interface. 2019 11, 28, 25186-25194

Keywords: CO₂ reduction, Photocatalyst, Black TiO₂, Sequential gas molecule