Hierarchical pore engineering in waste-derived carbons for supercapacitors: bridging the performance gap from three-electrode evaluation to practical two-electrode devices.

Supercapacitors based on waste-derived porous carbons have attracted significant attention due to their low cost, sustainability, and tunable pore structures. However, a persistent discrepancy remains between the high capacitance values reported in three-electrode (half-cell) configurations and the significantly lower performance observed in practical two-electrode devices. This gap is frequently overlooked, leading to overestimation of material performance and limiting the translation of laboratory-scale results into real applications. This review critically examines recent advances in hierarchical pore engineering of waste-derived carbons with a specific focus on understanding and bridging the performance gap between intrinsic material properties and device-level behaviour. We first analyse the fundamental differences between three-electrode and two-electrode evaluation systems, highlighting the origins of performance inflation that arise from low mass loading, restricted voltage windows, electrolyte effects, and the neglect of internal resistance. A quantitative and mechanistic framework is then established to explain the translation of capacitance from single-electrode to full-cell configurations. Building on this, structure-performance relationships are systematically evaluated across multiple studies to identify why materials with ultrahigh surface areas (>2000 m