The effect of CO₂ and H₂O molecule adsorption on SCN-Black TiO₂ during photocatalytic CO₂ reduction
Fang-Yu Fu1,2*, Tsai-Yu Lin2, Chiu-Ching Liao2, Putikam Raghunath4, Ming-Chang Lin4, Chih-I Wu1, Kuei-Hsien Chen3, Li-Chyong Chen2,5, Heng-Liang Wu2,5
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,
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