Understanding the role of hydrated metal chlorides in the salt-assisted synthesis of doped porous carbons

Porous nitrogen-doped carbons are promising for energy storage and gas adsorption, with performance governed by pore structure and surface chemistry. This study examines how hydrated alkali (LiCl, NaCl, KCl) and alkaline earth (MgCl 2 , CaCl 2 ) metal chlorides affect the carbonization of molecular precursors (adenine, guanine and glucose) through templating and composition-modifying effects. Alkali chlorides largely preserve precursor composition and exhibit minimal templating, with NaCl being mostly inert. In contrast, alkaline earth chlorides strongly influence carbonization. MgCl 2 functions as an effective templating agent while inducing significant compositional changes, producing highly porous carbons with high surface areas (up to 2648 m 2 /g) and modifying nitrogen configurations. CaCl 2 primarily acts as a template, generating porosity while maintaining precursor chemistry. Precursor structure also matters: adenine forms tubular morphologies with MgCl 2 , unlike guanine. Electrochemical measurements reveal that MgCl 2 -derived carbons, particularly adenine-MgCl 2 , showed the best performance in supercapacitors and Zn-ion capacitors due to their high surface area, accessible microporosity, and moderate nitrogen content. These results demonstrate that hydrated metal chlorides provide a simple strategy to tune the structure and chemistry of nitrogen-doped carbons through salt-assisted carbonization.