Graphene-based hydrogen storage devices

In the race to develop the next generation of clean fuel, hydrogen is on of the main contenders; an abundant element which that can react with ambient oxygen to release energy, leaving only water as waste product.

One of the main hurdles to overcome before hydrogen can become a widespread energy source in practical applications is the problem of hydrogen storage and transport, particularly for use in mobile applications.

 In this respect, the novel material graphene (single or few sheets of graphite) has recently attracted attention as a promising storage medium. Indeed, graphene is lightweight, chemically stable and exhibits attractive physico-chemical properties for hydrogen adsorption.

graphene

Fig.1: Flowing hydrogen (in white) over corrugated graphene (C-C bonds in gray) already loaded with chemisorbed H (in orange).

 Theoretical studies regarding chemically modified graphene suggest that it can adsorb up to 8 % mass ratio of hydrogen, which is close to the objectives of the US Department of Energy for hydrogen storage (9 wt% by 2015).For practical use as a storage medium, hydrogen should be released when needed, possibly without heating the device to high temperatures (several hundred centigrades).Objective of this project is the study, on experimental and theoretical footings, of the effects of modifications of corrugation, chemistry, and interplane spacing of graphene layers on hydrogen sorption.To this end, it is important that the interaction between hydrogen and graphene can be tuned by adjusting the distance between adjacent layers, by tuning the sheet curvature or by chemical functionalization of the material, thus enabling controlled adsorption and desorption of hydrogen.

Atomically resolved_STM_image_of_monolayer_graphene_on_SiC0001
Fig.2: Atomically resolved STM image of a monolayer of graphene on SiC(0001).

The possibility of implementing hydrogen storage systems activated through external magnetic fields and that work at constant temperature and pressure is under investigation. On-going activities include:
  • Synthesis and characterization of graphene on silicon carbide (SiC) and metal substrates (Fig. 2).
  • Studies of hydrogen adsorption and desorption on as-grown mono and few layer graphene.
  • Functionalization of graphene surfaces with chemical species to enhance hydrogen adsorption.
  • Controlled modification of graphene curvature and few layer graphene interplane separation to maximize hydrogen adsorption.
The facilities available at CNI@NEST laboratories include:
  • two dedicated chemical vapour deposition (CVD) systems for the production of graphene on SiC and on metals.
  • Atomic force microscopy (AFM).
  • Variable temperature UHV scanning tunnelling microscopy (STM) and spectroscopy (STS).
  • Scanning electron microscopy (SEM).
  • Transmission electron microscopy (TEM).
  • Raman spectroscopy.
  • Fourier transform infrared spectroscopy (FTIR).
  • Auger electron spectroscopy.
  • Highly sensitive gravimetric balances.
 Fig.3: Simulation of graphene curvature invertion and hydrogen desorption (click on image to watch movie).