Porous 3D Few‐Layer Graphene‐like Carbon for Ultrahigh‐Power Supercapacitors with Well‐Defined Structure–Performance Relationship

3D few-layer graphene-like carbon with hierarchical open porous architecture is obtained by a new in situ Cu template method, leading to top-level supercapacitive performance, especially state-of-the-art power density. An effective new approach is demonstrated, which can extend the understanding of structure-performance relationships for many electrochemical energy-storage systems and form a significant complement to classical electrochemical impedance spectroscopy.