Designing Thermally Compatible Template‐Coating Pairs Toward Dimensionally Stable 3D Porous Carbons with Tunable Density

Abstract The macroscale fabrication of 3D porous carbons with adjustable density and hierarchical architecture is crucial for emerging applications in energy storage, chemical separations, and lightweight structural materials. The pyrolytic conversion of polymer precursors is a common route to 3D porous carbon architectures, which typically relies on a single porous polymer precursor to function both as the structural blueprint and the carbon source. However, this approach can lead to substantial volume reduction, poor mass retention, and loss of architectural features, necessitating compromises between structural inheritance, dimensional stability, and control of density during pyrolysis. Here, a template‐coating platform is utilized to separate these conflicting requirements, facilitating independent optimization of mass and architecture. Specifically, a series of polybenzoxazine coatings is investigated to target early carbonization, minimal degradation, and high char yield. Concurrently, a complementary series of hierarchically porous polystyrene template architectures with tunable thermal properties is developed to meet synthetic and thermal compatibility criteria. The optimized template‐coating combination results in porous carbons that retain the architectural features of the template while maintaining their dimensional integrity (<10% linear shrinkage). By adjusting the coating weight fraction and pyrolysis temperature, we demonstrated a broad range of bulk densities (≈0.1–0.7 g cm ⁻³ ) while preserving structural and dimensional integrity (>80% volume retention). Importantly, these materials occupy a previously inaccessible region in the density‐retention landscape, showcasing low‐density porous carbons with minimal shrinkage (<20 vol%). This work presents a versatile design platform for the macroscale fabrication of structurally and dimensionally stable 3D porous carbons, allowing deterministic control over density across a wide range.