Nanohole-Structured and Palladium-Embedded 3D Porous Graphene for Ultrahigh Hydrogen Storage and CO Oxidation Multifunctionalities

Abstract

Atomic-scale defects on carbon nanostructures have been considered as detrimental factors and critical problems to be eliminated in order to fully utilize their intrinsic material properties such as ultrahigh mechanical stiffness and electrical conductivity. However, defects that can be intentionally controlled through chemical and physical treatments are reasonably expected to bring benefits in various practical engineering applications such as desalination thin membranes, photochemical catalysts, and energy storage materials. Herein, we report a defect-engineered self-assembly procedure to produce a three-dimensionally nanohole-structured and palladium-embedded porous graphene hetero-nanostructure having ultrahigh hydrogen storage and CO oxidation multifunctionalities. Under multistep microwave reactions, agglomerated palladium nanoparticles having diameters of ∼10 nm produce physical nanoholes in the basal-plane structure of graphene sheets, while much smaller palladium nanoparticles are readily impregnated inside graphene layers and bonded on graphene surfaces. The present results show that the defect-engineered hetero-nanostructure has a ∼5.4 wt % hydrogen storage capacity under 7.5 MPa and CO oxidation catalytic activity at 190 °C. The defect-laden graphene can be highly functionalized for multipurpose applications such as molecule absorption, electrochemical energy storage, and catalytic activity, resulting in a pathway to nanoengineering based on underlying atomic scale and physical defects.

Graphene decorated with metal nanoparticles: Hydrogen sorption and related artefacts

“…In agreement with theory, our recent experiments demonstrated that hydrogen sorption by r-GO and KOH activated r-GO (a-r-GO) follows standard trends and correlates with SSA values (~100-3300 m 2 /g range in our experiments) both at room temperature and 77K. [32][33][34] Nevertheless, reports on extremely high hydrogen uptakes (either in absolute values or relative to reported SSA) by various types of r-GO continue to appear, [35] outnumbering studies which find trivial uptake numbers. [36] In several cases the data presented as an evidence for exceptional hydrogen storage of graphene are represented by abnormal shapes of isotherms [35,37] or obtained by rather uncommon measurement methods.…”

“…Air-etched holey r-GO samples were reported earlier to show 5-fold increase of hydrogen sorption at 77K with a rather unusual shape of isotherms. [35] Our experiments confirmed that oxygen from air is etching the carbon support around Pt or Pd nanoparticles at high temperatures thus providing formation of holes in r-GO sheets.…”

“…[35]) and by microwave exfoliation have not showed significant difference after decoration with Pd and exhibited similar hydrogen storage properties. Additionally, we tested as precursor r-GO prepared by chemical reduction of graphene oxide (Graphenea) and have not found any significant difference with samples prepared using thermal or microwave exfoliation.…”

“…Finally, the mixture was treated in a microwave oven for 2 mins and cooled down to room temperature under argon protection. We prepared also several samples of "perforated graphene" by air annealing of r-GO and a-r-GO precursors using either rapid microwave treatment (following procedure given in ref [35]) or by heating in oven at 673-773K for 30-60 min. The weight of samples before and after the treatment was measured to control evaporation of carbon due to reaction with air and formation of gaseous reaction products.…”

“…[32][33][34] Nevertheless, reports on extremely high hydrogen uptakes (either in absolute values or relative to reported SSA) by various types of r-GO continue to appear, [35] outnumbering studies which find trivial uptake numbers. [36] In several cases the data presented as an evidence for exceptional hydrogen storage of graphene are represented by abnormal shapes of isotherms [35,37] or obtained by rather uncommon measurement methods. For example, ~4.6wt% uptakes already at 40bar and ambient temperatures were measured by Kim et al using quartz microbalance method.…”