Discovery of nanographene for hydrogen storage solving low reversibility issues

TL;DR

This study identifies nanographene with vacancy sites as a promising hydrogen storage material due to its high reversibility and low activation energy barriers for hydrogen uptake and release, based on density functional theory calculations.

Contribution

It introduces vacancy-centered hexagonal armchair nanographene as a novel material with self-catalytic properties for efficient hydrogen storage and release.

Findings

Hydrogen uptake and release barriers are nearly equal (~1.2 eV).

Dehydrogenation is slightly exothermic, hydrogenation slightly endothermic.

High coverage forms quintuply hydrogenated vacancies with exothermic release.

Abstract

We found good reversibility of hydrogen uptake-release in vacancy-centered hexagonal armchair nanographene (VANG) based on density functional theory calculation. VANG has a triply hydrogenated vacancy (V$_{111}$) at the center and acts as a self-catalytic property to reduce an activation barrier of hydrogen uptake-release. We found remarkable features in an almost equal value of the activation energy barrier of 1.19 eV for hydrogen uptake and 1.25 eV for hydrogen release on V$_{111}$ of VANG. The dehydrogenation showed slightly exothermic and the hydrogenation became slightly endothermic, suggesting the efficiency of hydrogen uptake-release. In high hydrogen coverage, the quintuply hydrogenated vacancy (V$_{221}$) is formed with some hydrogenated located in the in-plane and armchair edges. This structure produces an exothermic hydrogen release from the in-plane with an energy barrier of not more than 2 eV. This finding potentially addresses the low reversibility issues in the organic chemical hydrides as hydrogen storage materials.