Noble‐Metal‐Free Photocatalytic H2 Generation: Active and Inactive ‘Black’ TiO2 Nanotubes and Synergistic Effects

Abstract Over the past five years a number of different synthesis approaches has been reported to obtain so‐called ‘black’ titania. One of the outstanding features of the material is that certain synthesis processes lead to the formation of an intrinsic co‐catalytic center and thus enable noble‐metal free photocatalytic H2‐generation. In the present work, using TiO2 nanotube layers, we compare three common ‘blackening’ approaches, namely i) the original high‐pressure hydrogenation (HPT‐H2), ii) a classic high temperature reduction in Ar, and iii) an electrochemical (cathodic) reduction. We demonstrate that except for high pressure hydrogenation also cathodic reduction leads to an activation of TiO2 ‐ that is, it exhibits noble‐metal‐free photocatalytic H2 generation. Moreover, we show that a combination of cathodic reduction/high pressure hydrogenation leads to a synergistic effect, that is, a significant enhancement of the combined co‐catalytic activity.