The slurry was stirred by hand in the watch glass for 30 min under ambient conditions. The film was gradually formed upon drying of the slurry before being transferred to a glass surface, where it was kneaded with a spatula for 10 min to ensure homogeneous incorporation of the active material and PTFE and then rolled into a freestanding film using a homemade aluminium rolling pin. The film was dried in vacuo at 90 degrees for at least 24 h to remove any excess ethanol. The masses of components were calculated so that the final film had a composition of 95 wt.% functionalized carbon material and 5 wt.% PTFE. The same procedure was used for all freestanding composite films and all films had a thickness of ca. 250 𝜇m.