Unexpected effect of stacking manner of covalent triazine polymer on photocatalytic hydrogen production

Abstract

Photocatalytic water splitting has been considered as a promising approach to generate H2 for addressing energy crisis and environmental issues. Herein, we fabricated two novel covalent triazine polymers (CTP), the compact CTP-TG-1 (TG is abbreviation of Tiangong University) and incompact CTP-TG-2, to explore the effect of stacking manner of 2D semiconductor on photocatalytic H2 production. The compact CTP-TG-1 shows excellent H2 production rate of 7066.15 µmol h−1 g−1. Meanwhile, the incompact counterpart, CTP-TG-2, which was constructed by tridimensional monomer, exhibits quite low H2 production rate of 171.65 µmol h−1 g−1. Although the two CTPs possess similar intrinsic features in visible-light absorbance, charge-carrier lifetime and energy level, the electrochemical measurements indicate that the compact CTP-TG-1 possesses faster charge-carrier transport, which is crucial for photocatalytic H2 generation. For the compact CTP-TG-1, the hot π-electrons in each 2D layer not only can migrate within the 2D plane, but also tunnel through 2D interlayer and then to Pt NPs on the surface for H2 generation. In contrast, owing to the large distance of loose 2D interlayer, the incompact CTP-TG-2 shows much lower photocatalytic activity as a result of the suppressed hot π-electrons tunneling. Furthermore, we designed and synthesized other three CTPs, including compact CTP-TG-4 and CTP-TG-5 and incompact CTP-TG-3. As expected, the compact CTP-TG-4 and CTP-TG-5 display one order of magnitude higher photocatalytic activity than that of the compact CTP-TG-3, further confirming the significant contribution of 2D stacking manner on photocatalytic hydrogen production.