Fabrication of porous carbon films and their applications for electrocatalytic electrodes

Porous polyacrylonitrile (PAN) films spin coated on a quartz substrate with subsequent drying under humid conditions were used for preparing porous carbon films (PCFs) through conventional heat treatments such as stabilization and carbonization. The drying time, relative humidity (RH), and concentration of the PAN solution affected the morphology of the porous surface without significantly changing the intrinsic properties of the carbon films as thick as ~1.5 μm. The pores were present even after the heat treatments, and the resulting carbonized PAN films had pores with an average diameter and depth of up to ~1.2 μm and ~200 nm, respectively. The resulting PCFs were used as FTO-free counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The PCF-CEs displayed high electrical conductivity with a sheet resistance of ~12 Ω/sq. Furthermore, PCFs showed superior charge transfer properties at CE/electrolyte interfaces and increased current exchange for electrochemical iodine reduction. The DSSCs using PCF-CEs dried for 120 min showed significantly improved power conversion efficiency (PCE, 5.24%) and fill factor (FF, 0.48) compared to those using carbon nanosheet CEs (PCE, 4.46%; FF, 0.4), because of the advantageous and synergistic electrical and morphological improvements. This work provides a promising class of potential materials that can be used as electrocatalytic electrodes in electrochemical devices.