Mechanisms of adsorbing hydrogen gas on metal decorated graphene

TL;DR

This paper investigates how decorating graphene with different metals affects hydrogen adsorption, identifying three distinct mechanisms and highlighting the tunability of Kubas adsorption via electric fields for improved hydrogen storage.

Contribution

The study systematically analyzes metal-decorated graphene for hydrogen storage, revealing three adsorption mechanisms and demonstrating electric field tuning of Kubas adsorption.

Findings

Identified three hydrogen adsorption mechanisms on metal decorated graphene.

Demonstrated electric field can modulate Kubas adsorption.

Provided insights into optimizing graphene-based hydrogen storage materials.

Abstract

Hydrogen is a key player in global strategies to reduce greenhouse gas emissions. In order to make hydrogen a widely-used fuel, we require more efficient methods of storing it than the current standard of pressurized cylinders. An alternative method is to adsorb H$_2$ in a material and avoid the use of high pressures. Among many potential materials, layered materials such as graphene present a practical advantage as they are lightweight. However, graphene and other 2D materials typically bind H$_2$ too weakly to store it at the typical operating conditions of a hydrogen fuel cell. Modifying the material, for example by decorating graphene with adatoms, can strengthen the adsorption energy of H$_2$ molecules, but the underlying mechanisms are still not well understood. In this work, we systematically screen alkali and alkaline earth metal decorated graphene sheets for the adsorption of hydrogen gas from first principles, and focus on the mechanisms of binding. We show that there are three mechanisms of adsorption on metal decorated graphene and each leads to distinctly different hydrogen adsorption structures. The three mechanisms can be described as weak van der Waals physisorption, metal adatom facilitated polarization, and Kubas adsorption. Among these mechanisms, we find that Kubas adsorption is easily perturbed by an external electric field, providing a way to tune H$_2$ adsorption.