# Laser-Processed 2D Germanane on Graphene for Organohydrogel-Based Zinc-Ion Hybrid Capacitors

## TL;DR

This paper explores using laser-processed germanane on graphene to improve zinc-ion capacitor performance.

## Contribution

A new method for in situ decoration of 2D germanane sheets on laser-induced graphene for energy storage is introduced.

## Key findings

- HGe-decorated LIG shows high Zn2+ storage capacity in aqueous electrolyte.
- MGe-decorated LIG exhibits excellent cyclic stability with 83% capacity retention after 12,000 cycles.

## Abstract

Group
14 monoelemental
two-dimensional (2D) materials beyond graphene,
such as silicene and germanene, have gained significant attention
in the scientific community. Covalent functionalization of germanene
with hydrogen and methyl leads to germanane (hydrogen/methyl-terminated
germanene; HGe/MGe). While the optical and electronic properties of
HGe and MGe were explored previously, there is no report on their
zinc ion storage electrochemistry. Though the layered HGe/MGe sheets
have tunable interlayer spacing, which cushions the volume expansion
during ion storage, their inferior electrical conductivity limits
the charge transfer kinetics. Herein, we demonstrate a single-step,
facile approach for in situ decoration of 2D HGe/MGe sheets over laser-induced
graphene (LIG) using a pulsed laser and examine their morphological,
chemical, and electrochemical (EC) characteristics. The HGe/MGe-decorated
LIG is tested as a cathode for a zinc ion hybrid capacitor (ZHC) in
an aqueous electrolyte and polyacrylamide organohydrogel to unveil
the selective sites for zinc ion electrochemistry by experimental
and theoretical aspects. This ZHC design enables a notable Zn2+ storage capacity (104 F g–1 @ 0.25 A g–1 in aqueous electrolyte) for HGe-decorated LIG, whereas
MGe-decorated LIG records impressive cyclic stability (capacity retention
83% after 12000 cycles). Density functional theory calculations elucidate
favorable adsorption of Zn at MGe and HGe networks. These findings
summarize the applicability of 2D functionalized germanane, which
has the potential to expand by numerous alkyl chains and terminal
groups for targeted energy storage applications.