Understanding the Wettability of C₁N₁ (Sub)Nanopores: Implications for Porous Carbonaceous Electrodes

Understanding how water interacts with nanopores of carbonaceous electrodes is crucial for energy storage and conversion applications. A high surface area of carbonaceous materials does not necessarily need to translate to a high electrolyte-solid interface area. Herein, we study the interaction of water with nanoporous C₁N₁ materials to explain their very low specific capacitance in aqueous electrolytes despite their high surface area. Water was used to probe chemical environments, provided by pores of different sizes, in ¹H MAS NMR experiments. We observe that regardless of their high hydrophilicity, only a negligible portion of water can enter the nanopores of C₁N₁, in contrast to a reference pure carbon material with a similar pore structure. The common paradigm that water easily enters hydrophilic pores does not apply to C₁N₁ nanopores below a few nanometers. Calorimetric and sorption experiments demonstrated strong water adsorption on the C₁N₁ surface, which restricts water mobility across the interface and impedes its penetration into the nanopores.