Advanced Photocatalysts: Pinning Single Atom Co‐Catalysts on Titania Nanotubes

Xin Zhou,Karsten Meyer,Radek Zboril,Imgon Hwang,Anca Mazare,Patrik Schmuki,Ondřej Tomanec,Dominik Fehn

doi:10.1002/adfm.202102843

Abstract

AbstractSingle atom (SA) catalysis, over the last 10 years, has become a forefront in heterogeneous catalysis, electrocatalysis, and most recently also in photocatalysis. Most crucial when engineering a SA catalyst/support system is the creation of defined anchoring points on the support surface to stabilize reactive SA sites. Here, a so far unexplored but evidently very effective approach to trap and stabilize SAs on a broadly used photocatalyst platform is introduced. In self‐organized anodic TiO2 nanotubes, a high degree of stress is incorporated in the amorphous oxide during nanotube growth. During crystallization (by thermal annealing), this leads to a high density of Ti3+‐Ovsurface defects that are hardly present in other common titania nanostructures (as nanoparticles). These defects are highly effective for SA iridium trapping. Thus a SA‐Ir photocatalyst with a higher photocatalytic activity than for any classic co‐catalyst arrangement on the semiconductive substrate is obtained. Hence, a tool for SA trapping on titania‐based back‐contacted platforms is provided for wide application in electrochemistry and photoelectrochemistry. Moreover, it is shown that stably trapped SAs provide virtually all photocatalytic reactivity, with turnover frequencies in the order of 4 × 106h−1in spite of representing only a small fraction of the initially loaded SAs.

Highlights

Single atom (SA) catalysis, over the last 10 years, has become a forefront in concentration of remaining finely dispersed Au or Pt atoms in a surface trapped Meδ+ state heterogeneous catalysis, electrocatalysis, and most recently in photoca
During crys- of “classic” heterogeneous catalysis reactallization, this leads to a high density of Ti3+-Ov surface defects that are hardly present in other common titania nanostructures
In self-organized anodic TiO2 nanotubes, such as in Figure 1a, during the growth of the amorphous oxide nanotube-structure, considerable strain is embedded in the tube walls.[38,39]

Summary

Results and Discussion

In self-organized anodic TiO2 nanotubes, such as in Figure 1a, during the growth of the amorphous oxide nanotube-structure, considerable strain is embedded in the tube walls.[38,39] This. The EDX results are in rough agreement with a more accurate determination of the integral Ir loading of the structures by powder analysis (using atomic absorption spectroscopy, AAS), where we obtain 0.58% for the nanotubes and 0.84% for the anatase nanoparticles, that is, the NTs and the NPs show a similar integral Ir loading in spite of a drastically different density of Ti3+-OV defect states This indicates that only a minor fraction of Ir is trapped by galvanic displacement and as a consequence suggests that the drastically different photocatalytic reactivity of the two morphologies is due to a large difference in “truly” active sites.

Conclusion

Experimental Section

Data Availability Statement