Carbazole-Based Thin Microporous Polymer Films for Photocatalytic Hydrogen Evolution

Photocatalytic hydrogen evolution is a direct pathway to store solar energy in chemicals. Conjugated microporous polymers (CMPs) are porous organic photocatalysts, that are typically applied in powder form in heterogenous catalytic reactions. However, the use of powder photocatalysts in dispersion poses some major challenges when it comes to practical applications in larger scales. In this manuscript, the photocatalytic performance of a carbazole-based porous organic polymer (C-POP) film produced by electro polymerizing 1,2,3,5-Tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) is investigated, well-known for its intriguing photocatalytic properties. The thickness of the intrinsic microporous film is tuneable by the amount of cyclic voltammetry cycles but it is shown that the hydrogen production is not dependent on film thickness. It can therefore be concluded that catalysis is mainly occuring on the outer surface of the films, questioning whether high surface areas are always required for efficient photocatalysis. A microstructured film offers the advantage that, with a reduced amount of polymer material, a constant or even increased external surface area of the film can be achieved. The approach presented here is therefore advantageous for achieving high hydrogen production per unit area with minimal amounts of polymer, as very thin layers are already sufficient for high activity.