# Stepwise De‐solvation and Diffusion Kinetics of Hydrated Zn‐ion in Hierarchical Porous Carbon Anode for Improved EDLC Behavior

## TL;DR

This paper shows how designing hierarchical pores in carbon anodes improves zinc-ion supercapacitor performance by enabling efficient ion transport and energy storage.

## Contribution

The study introduces a stepwise de-solvation mechanism of hydrated Zn-ions in hierarchical micropores to enhance EDLC behavior in ZiHSCs.

## Key findings

- Stepwise de-solvation of [Zn(H2O)6]2+ reduces de-solvation energy and improves diffusion kinetics.
- The optimized anode achieves 224.1 mAh/g capacitance and 99.1% capacity retention over 100,000 cycles.
- In situ and ex situ analyses confirm rapid micropore filling and removal of bound water during discharge.

## Abstract

Porous carbon (PC) is widely recognized as a promising anode material for zinc‐ion hybrid supercapacitors (ZiHSCs), but its practical deployment is hindered by sluggish ion diffusion kinetics and poor rate performance. In this study, a stepwise de‐solvation of hydrated Zn‐ion is observed during migration within the hierarchical micropore channels characterized by dominated dimension of 0.74 and 1.54 nm. This phenomenon mitigates the free energy dissipation of hydrated Zn‐ion diffusion, accelerates charge transfer kinetics, and substantially enhances the EDLC generation. In situ Raman, ex situ FT‐IR and XPS analysis reveal an intensive removal of bound water from [Zn (H2O)6]2+ and rapid micropore filling at the discharge state. The optimized anode delivers a specific capacitance of 224.1 mAh/g at 0.2 A/g, an impressive energy density of 179.6 Wh/kg (active materials basis), and exceptional cycling stability (99.1% capacity retention over 100,000 cycles). This dimension design paradigm establishes a generalizable framework for optimizing porous carbons in energy storage, bridging the gap between fundamental ion‐solvent‐pore interactions.

The size mismatch between the micropore channel and [Zn(H2O)6]2+ in porous carbon anode during the discharge process was addressed by regulating the hierarchical channel. The inducted stepwise de‐solvation of [Zn(H2O)6]2+ significantly reduced its de‐solvation energy, promoted the EDLC behavior, and strengthened the diffusion kinetic.