New Progress in Molecular Hydrogen Formation from Photocatalysis of Methanol on Anatase-TiO2(101)

The DICP Research Group led by Prof. YANG Xueming has carried out a systematic study on “Molecular Hydrogen Formation from Photocatalysis of Methanol on Anatase-TiO₂(101).” The results were published in the recent issue of the recent issue of the Journal of American Chemical Society(J. Am. Chem. Soc., 2014, 136 (2), 602–605) .

Rutile and anatase TiO₂ materials have been often used in the study of hydrogen (H₂) production from photocatalytic water splitting, and previous study found that adding methanol (CH₃OH) to pure water solution can dramatically enhance H₂ production, implying that CH₃OH played a crucial role in H₂ production. Despite lots of work focusing on rutile (R)-TiO₂, the anatase form is the most active polymorph in commercial applications for catalysis actually. Even though a lot of photocatslysis studies have been carried out on anatase (A)-TiO₂ particles, very little was done on well-defined surfaces.  

In a recent study, we have shown that photocatalytic dissociation of CH₃OH on TiO₂(110) occurs in a stepwise manner.( J. Am. Chem. Soc., 2012, 134 (32), 13366–13373). And D₂ can be formed via thermal recombination of dissociated D-atoms on the bridge bonded oxygen (BBO) sites from photocatalysis of fully deuterated CH₃OH, suggesting that the last molecular D₂ formation step on the R-TiO₂(110) surface is a thermally driven process. Since only about 7% of D-atoms on the BBO sites contribute to D₂ formation with most D-atoms recombining with BBO atoms to form D₂O, it implies that H₂ formation is not the most efficient process on R-TiO₂(110). (J. Am. Chem. Soc., 2013, 135 (28), 10206–10209). In this work, we have investigated molecular H₂ formation on A-TiO₂(101) from photocatalysis of CH₃OH. Our results show that H₂ is formed via thermal recombination of dissociated H-atoms on the BBO sites from photocatalysis of CH₃OH on A-TiO₂(101). The H atoms at the O_BBO sites mostly come off as H₂ on the A-TiO₂(101) surface, not taking an O_BBO to form H₂O (the O_BBO atoms on A-TiO₂(101) are much more stable than on R-TiO₂(110)). About 40% of the H atoms at the O_BBO sites come off as H₂ on A-TiO₂(101), While only 7% of D-atoms on the BBO sites on R-TiO₂(110) contribute to D₂ formation, suggesting that the H₂ formation process is more efficient on A-TiO₂(101). The present investigation of the mechanism of H₂ formation from UV CH₃OH photocatalysis on A-TiO₂(101) could help us to understand the nature of H₂ production on TiO₂ photocatalysts. (By XU Chenbiao and GUO Qing)