Hydrogen Storage In Graphene Research Articles

Controlling the electrochemical hydrogen generation and storage in graphene oxide by in-situ Raman spectroscopy

Hydrogen, generated from water splitting, is postulated as one of the most promising alternatives to fossil fuels. In this context, direct hydrogen generation by electrolysis and fixation to graphene oxide in an aqueous suspension could overcome storage and distribution problems of gaseous hydrogen. This study presents time-resolved determination of the electrochemical hydrogenation of GO by in-situ Raman spectroscopy, simultaneous to original functional groups elimination. Hydrogenation is found favoured by dynamic modulation of the electrochemical environment compared to fixed applied potentials, with a 160% increase of C–H bond formation. Epoxide groups suppression and generated hydroxide groups point at these epoxide groups being one of the key sites where hydrogenation was possible. FTIR revealed characteristic symmetric and asymmetric stretching vibrations of C–H bonds in CH 2 and CH 3 groups. This shows that hydrogenation is significantly also occurring in defective sites and edges of the graphene basal plane, rather than H-Csp 3 groups as graphane. We also determined a −0.05 V RHE reduction starting potential in alkaline electrolytes and a 150 mV cathodic delay in acid electrolytes. The identified key parameters role, together with observed diverse C-H x groups formation, points at future research directions for large-scale hydrogen storage in graphene.

Migration and desorption of hydrogen atom and molecule on/from graphene

Migration and desorption of hydrogen atom and molecule on/from graphene are crucial for understanding mechanism of the hydrogen storage in graphene and graphene synthesis. All possible hydrogen atom migration, hydrogen atom and hydrogen molecule desorption from single layer graphene have been studied systematically by using functional density theory B3LYP/6-31G(d). Our results show that the hydrogen atom desorption is energetically favorable with the lowest desorption barrier of 149.3 kJ mol−1 from stable hydrogen adsorption sites, while the migration is restricted due to high barriers which are greater than 191.0 kJ mol−1. Hydrogen molecular desorption is possible only from edge adsorbed hydrogen atom due to its comparable barrier of 149.9 kJ mol−1. Other hydrogen molecular desorption pathways are less likely due to small population of the reaction species.

Effect of nitrogen doping and external electric field on the adsorption of hydrogen on graphene

Effect of doping and external electric field on the adsorption of hydrogen on graphene was studied by using density functional theory. Substitutional nitrogen, pyridinic and pyrrolic nitrogen doping has been considered. It was found that hydrogen prefers to be physically adsorbed on the pristine and substitutional nitrogen doped graphene, whereas hydrogen prefers to be chemically adsorbed on the pyridinic and pyrrolic nitrogen doped graphene. An external electric field can enhance the chemical adsorption of hydrogen on the pyridinic and pyrrolic N-doped graphene. These demonstrate nitrogen doping combined with external electric field can increase the capacity of hydrogen storage in graphene.

Electric field manipulated reversible hydrogen storage in graphene studied by DFT calculations

AbstractEnhancement of hydrogen storage capacity is a great challenge that the research community is facing. The challenge lies on the fact of interdependence of hydrogen storage and release processes. It presents that the hydrogen release would be difficult if the hydrogen can be stored easily or vice versa. This work strategically tackles this critical issue through density functional theory (DFT) calculations by applying defect engineering on graphene, and also changing the hydrogenation/dehydrogenation and hydrogen diffusion chemical potentials via applying electric field. It is found that hydrogen molecules are dissociatively adsorbed on N‐doped graphene spontaneously in the presence of a perpendicular electric field F. After adsorption, H atoms diffuse on N‐doped graphene surface with low energy barrier and the graphene can be fully hydrogenated. By removing the electric filed, the stored hydrogen can be released efficiently under ambient conditions. It demonstrates that the N‐doped graphene is a promising hydrogen storage material with the storage capacity up to 6.73 wt%. The electric field can act as a switch for hydrogen uptake/release processes.

(Invited) Prospects for Hydrogen Storage in Graphene

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Prospects for hydrogen storage in graphene

Hydrogen-based fuel cells are promising solutions for the efficient and clean delivery of electricity. Since hydrogen is an energy carrier, a key step for the development of a reliable hydrogen-based technology requires solving the issue of storage and transport of hydrogen. Several proposals based on the design of advanced materials such as metal hydrides and carbon structures have been made to overcome the limitations of the conventional solution of compressing or liquefying hydrogen in tanks. Nevertheless none of these systems are currently offering the required performances in terms of hydrogen storage capacity and control of adsorption/desorption processes. Therefore the problem of hydrogen storage remains so far unsolved and it continues to represent a significant bottleneck to the advancement and proliferation of fuel cell and hydrogen technologies. Recently, however, several studies on graphene, the one-atom-thick membrane of carbon atoms packed in a honeycomb lattice, have highlighted the potentialities of this material for hydrogen storage and raise new hopes for the development of an efficient solid-state hydrogen storage device. Here we review on-going efforts and studies on functionalized and nanostructured graphene for hydrogen storage and suggest possible developments for efficient storage/release of hydrogen under ambient conditions.

Enhanced Hydrogen Storage in Graphene Oxide‐MWCNTs Composite at Room Temperature

AbstractHigh hydrogen capacity (up to 2.6 wt%) is reported for highly aligned structures of Graphene oxide‐Multiwalled carbon nanotubes composite at room temperature. It is demonstrated that the scalable liquid crystal route can be employed as a new method to prepare unique 3‐D framework of graphene oxide layers with proper interlayer spacing as building blocks for cost‐effective high‐capacity hydrogen storage media. The strong synergistic effect of the intercalation of MWCNTs as 1‐D spacers within graphene oxide frameworks resulted in unrivalled high hydrogen capacity at ambient temperature. The mechanisms involved in the intercalation procedure are fully discussed. The main concept behind intercalating one‐dimensional spacers in between giant GO sheets represents a versatile and highly scalable route to fabricate devices with superior hydrogen uptake.

Hydrogen storage in graphene decorated with Pd and Pt nano-particles using an electroless deposition technique

Graphene samples prepared by the exfoliation of graphitic oxide were decorated with platinum (Pt) and palladium (Pd) by an electroless deposition technique. The obtained composites were attempted to be used as hydrogen storage materials. The composites were characterized by transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The porous texture of all graphenes was analyzed using nitrogen adsorption isotherms at 77 K. The hydrogen adsorption was accurately measured by a volumetric adsorption apparatus at 303 K up to 5.7 MPa. The mesopores that originated from the space between exfoliated graphene sheets were observed by nitrogen adsorption isotherms on all graphene samples. Structure investigations reveal that specific surface areas apparently decrease after Pd or Pt decoration. The Pt and Pd nanoparticles of 2–5 nm diameter homogeneously dispersed on the exfoliated graphene sheets and voids of graphene sheets. Experimental results show that Pd or Pt decoration doubles the hydrogen capacity supporting the existence of the hydrogen spillover effect in Pd- or Pt-graphene systems.