Toward record high Zn2+ storage in carbon electrodes via pore confinement engineering

Abstract

The Zn²⁺ storage capability of carbon cathodes for aqueous zinc-ion hybrid supercapacitors (ZHSCs) is seriously restricted by the mismatch between the pore size and charge-carrier ion sizes. Herein, the effective specific surface area (ESSA) which is determined using the specific surface area (SSA) and the well-matched pore size with hydrated Zn²⁺, is proposed to pinpoint the connection between pore structural properties of carbon and Zn²⁺ storage behavior. The ESSA with a pore confinement range from 0.64 to 2.5 nm within carbon is confirmed to be the most suitable for maximum storage of Zn²⁺. As such, Zn//BPC-3, with the highest ESSA, achieves a record high specific capacity of 290 mA h g⁻¹ at 0.3 A g⁻¹ and outstanding cyclability (95.6% capacity retention after 65 000 cycles) by matching the hydrated Zn²⁺ size with the pore structure of electrode materials. Furthermore, multiple operando spectroscopy techniques reveal that the hydrated Zn²⁺ and SO₄²⁻ are adsorbed and exchanged within the pores (sizes larger than 0.64 nm), where H⁺ adsorption/desorption, with a self-regulating pH microenvironment, are accompanied at the carbon cathode–electrolyte interface, finally achieving efficient charge storage. This work will provide a new insight into the structure-driven charge storage mechanism and rational design of high-energy/power-density ZHSCs.