To further enhance the activity of the catalyst, the chloride ions on the Pt centers were replaced with iodide to give the POM-PtI cluster (see synthetic discussion above for details). When employed for light-driven HER under identical conditions as described above, POM-PtI showed significantly higher activity with a maximum TON of ca. 740 after tirradiation = 10 h (Figure ). Note that the higher reactivity of POM-PtI compared with POM-PtCl is in line with previous reports: