Cation-Dependent Salt Templating of Phenolic Resin-Derived Hierarchical Porous Carbon for High-Performance Supercapacitors

High-surface-area porous carbon electrodes that feature a well-balanced pore distribution and facilitate rapid ion transport are crucial for enhancing electric double-layer capacitors. Conventional phenolic resin-derived carbons are usually dominated by micropores and show limited pore connectivity, which restricts electrolyte infiltration and rate performance. Herein, we report a cation-dependent salt-templating strategy by introducing equimolar ZnCl2, MgCl2, and MnCl2 into a resorcinol–hexamethylenetetramine hydrothermal system. The three divalent cations direct markedly different carbon-framework evolution. Zn2+ mainly promotes micropore formation and smaller carbon spheres, Mg2+ favors particle fusion and larger pores, whereas Mn2+ converts discrete microsphere assemblies into a continuous three-dimensional hierarchical porous network. Among the resulting samples, PC-Mn exhibits a specific surface area of 1459 m2 g–1, a total pore volume of 1.12 cm3 g–1, and a micropore surface area measuring 1105 m2 g–1, along with well-developed mesoporous channels ranging from 2 to 4 nm. When tested in 6 M KOH, PC-Mn reaches a capacitance of 270.15 F g–1 and maintains 182.49 F g–1 at a current density of 20 A g–1, achieving a capacitance retention of 95.6% following 10,000 cycles. Furthermore, the PC-Mn symmetric supercapacitor exhibits a specific capacitance of 252.04 F g–1 and an energy density of 21.24 Wh kg–1 at a power density of 20,123 W kg–1. These results demonstrate that regulating the divalent cation species in salt-templated phenolic resin systems provides an effective approach for tailoring hierarchical pore structures and improving the electrochemical performance of porous carbon electrodes.