Synthesis of Phenol–Formaldehyde Resin-Derived Multiporous Carbons with Tunable Micro/Mesoporous Structures through One-Pot Wet Mixing and Nano-CaCO3-Assisted Activation for High-Performance Organic-Electrolyte Supercapacitors

Abstract

Porous carbons are widely used as electrode materials for electric double-layer capacitors (EDLCs), but their high-rate performance in organic electrolytes is governed more by transport-limited accessibility than by BET surface area alone. Here, a wet one-pot strategy integrating KOH activation with nano-CaCO3-assisted pore engineering was developed to construct phenol–formaldehyde-derived multiporous carbons (MPCs) as a model platform for establishing process–structure–performance relationships. By systematically varying the activation temperature, pre-carbonization temperature, and activation time, the coupled evolution of pore architecture, carbon microstructure, and product yield was clarified. Higher activation severity increased accessible porosity and promoted a micro-to-meso shift, whereas pre-carbonization favored mesopore-dominant pore development under fixed activation conditions. At a constant activation temperature of 950 °C, activation time acted as a structural knob that balanced pore accessibility and the local ordering of sp2 carbon domains. Device-level evaluation in symmetric CR2032 coin cells using 1.0 M TEABF4/PC showed that high-rate capacitance utilization is governed more directly by impedance-limited accessibility than by nominal surface area alone. Under the fixed PF:KOH:CaCO3 ratio of 1:1.5:1.5, activation at 950 °C for 3 h provided the most practical operating condition, combining low electrochemical losses (Rct ≈ 0.65 Ω; IR drop ≈ 0.195 V), a reduced thermal budget, and improved process economy, as reflected by a carbon yield of 30% and a yield-normalized surface area (YSA) of 449 m2 g–1, while delivering 81% rate retention and 13.6 Wh kg–1 at approximately 8.5 kW kg–1. These findings establish an impedance-aware design framework for MPC electrodes in organic-electrolyte EDLCs.