Dual ion relay storage mechanism in hierarchical porous carbon electrode for aqueous zinc-ion hybrid capacitors

Abstract

Aqueous zinc-ion hybrid capacitors (ZIHCs) are promising for sustainable energy storage, but their specific capacity is severely limited by the kinetic and capacity mismatch between capacitive carbon cathodes and zinc anodes. Herein, we present a synergistic space-confinement and activation strategy to synthesize hierarchical porous carbon nanosheets (CMK-x, x represents the pyrolysis temperature) derived from coal tar pitch. The optimized CMK-700 features a high specific surface area of 2223.9 m²·g⁻¹ and a maximized ultramicropores volume of 0.4836 cm³·g⁻¹. Combined ex-situ characterization and molecular dynamics simulations, a unique dual-ion relay storage mechanism enabled by spatial domain separation across different pore structures was unraveled. Specifically, the larger [Zn(H₂O)₆]²⁺ ions are stored in larger micropores (> 1 nm) at a voltage window of 0.3–1.9 V, while smaller hydrated protons ([H₃O]⁺) act as ‘charge relays’ to penetrate the ultramicropores below 0.3 V. Such a proton accommodation through reversible chemical hydrogen adsorption/desorption contributes significant surface pseudocapacitance. Consequently, the assembled ZIHCs deliver an impressive high specific capacity of 368.1 mAh·g⁻¹ at 0.5 A·g⁻¹ and outstanding long-term stability with 86.39% capacity retention after 21000 cycles. This work provides new insights into designing high-performance ZIHC cathodes through the strategic integration of a dual-ion relay storage mechanism.

Graphical abstract

Keywords

hierarchical porous carbon / ultramicropore structure / dual ion relay storage / electrochemical performance / zinc-ion hybrid capacitors

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