Graphene oxide films developed for a range of technical applications

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(Left): Schematics of side view showing oxygen gas permeating through graphene oxide, GO (top) and reduced graphene oxide, rGO (bottom). For the case of GO, oxygen molecules permeates through the interlayer due to presence of oxygen functional groups acting as “bridges”. However, pristine graphene nanoislands created by removal of oxygen group “bridges” clog permeation paths (dashed boxes), increasing the diffusion length as illustrated in top view. (Right): Possible permeation paths of the oxygen are indicated by the black and gray arrows for GO and rGO, respectively.

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In two recent publications, Los Alamos researchers and collaborators examine graphene oxide films. These films have applications for a range of technologies, including energy, catalysis, sensing, and gas/moisture barriers. The research is described in the following sections.

Building reduced graphene oxide thin films as ultrabarriers for organic electronics

Gas barrier films are crucial to a wide range of products used in food packaging, ship coatings, water/gas purification, and electronic device packaging. In 2010, the global market for gas barrier films involving the packaging industry was $130 billion and is expected to grow to $171 billion by 2016, according to a SmithersPira report. Development of high performance gas and moisture barrier films is therefore of significant importance.

In Advanced Energy Materials, Materials Synthesis and Integrated Devices (MPA-11) scientists working with collaborators from Rutgers University, Georgia Institute of Technology, and Tohoku University (Japan) report that properly stacking atomically thin sheets of carbon, specifically graphene oxide, leads to bulk thin films that prevent oxygen/moisture penetration better than current commercially available polymer-chain based barrier films. The results provide a new route for the design and preparation of high-performance and solution-processable gas/moisture barriers, which have potential applications for a wide range of encapsulation technologies.

Taking advantage of the unique properties of graphene, which prevents even the smallest atoms of hydrogen to pass due to its close-packed hexagonal structure, the team developed a scalable chemical route to produce the reduced graphene oxide material. The researchers filtered the material to form thin films. They applied their barrier films to working organic photovoltaic devices (OPVs) and monitored device performance over time. The team chose OPVs due to their high sensitivity to environmental conditions (i.e., oxygen and moisture levels). The new films made by this process resulted in substantial improvements in OPV lifetime relative to devices without a barrier layer as well as devices encapsulated in commercially available polymer-chain-based barrier films.

Figure 4. (Left): Schematics of side view showing oxygen gas permeating through graphene oxide, GO (top) and reduced graphene oxide, rGO (bottom). For the case of GO, oxygen molecules permeates through the interlayer due to presence of oxygen functional groups acting as “bridges”. However, pristine graphene nanoislands created by removal of oxygen group “bridges” clog permeation paths (dashed boxes), increasing the diffusion length as illustrated in top view. (Right): Possible permeation paths of the oxygen are indicated by the black and gray arrows for GO and rGO, respectively.

Reference: “Reduced Graphene Oxide Thin Films as Ultrabarriers for Organic Electronics,” Advanced Energy Materials 4, 1300986 (2014); doi: 10.1002/aenm.201300986. Authors include Hisato Yamaguchi (MPA-11 and Rutgers University), Wanyi Nie, Gautam Gupta, and Aditya Mohite (MPA- 11); Jimmy Granstrom, Hossein Sojoudi, and Samuel Graham (Georgia Institute of Technology); Takeshi Fujita and Mingwei Chen (Tohoku University, Japan); Damien Voiry and Manish Chhowalla (Rutgers University).

A Laboratory Directed Research and Development (LDRD) program Director’s Postdoctoral Fellowship funded the Los Alamos portion of the work. The research supports the Laboratory’s Energy Security mission area and Materials for the Future science pillar. Technical contact: Aditya Mohite

Ozonated graphene oxide film as a proton-exchange membrane

In research published as a “hot paper” and showcased on the frontispiece of the communication section of Angewandte Chemie, a high-impact applied chemistry journal, LANL researchers and collaborators describe a new self-supported proton-exchange membrane composed of ozonated graphene oxide (GO) incorporated into a polymer electrolyte fuel cell. Their results suggest that GO derivatives could become a carbon-based, non-polymeric alternative to Nafion® for hydrogen fuel cell, supercapacitor, catalysis, and sensing applications.

Soon after the discovery of graphene, GO began attracting considerable interest because of its unique electronic and optical properties. Graphene oxide contains several chemical functional groups that are attached to the graphite basal plane and can be manipulated to tailor GO for specific applications. The new study demonstrates that modifying dispersed GO presents a powerful opportunity to optimize a nanoscale material for proton exchange membranes. The researchers revealed that the reaction of GO with ozone results in a high level of oxidation, which leads to significantly improved ionic (protonic) conductivity of the GO. The team synthesized freestanding ozonated GO films and used them as efficient proton-conducting electrolytes for fuel cell membranes. The increase in protonic conductivity of the ozonated GO originates from enhanced proton hopping, which is due to the higher content of oxygenated functional groups in the basal planes and edges of ozonated GO as well as the morphological changes in GO caused by ozonation.

Reference: “Ozonated Graphene Oxide Film as a Proton-Exchange Membrane,” Angewandte Chemie International Edition 53, 3588 (2014); doi: 10.1002/anie.201310908. The lead author is Director’s Postdoctoral Fellow Wei Gao. Coauthors include W. Gao, G. Wu, R. Mukundan, E. L. Brosha, A. M. Dattelbaum, and P. Zelenay (Materials Synthesis and Integrated Devices, MPA-11); J. K. Baldwin (Center for Integrated Nanotechnologies, MPA-CINT); M.T. Janicke; D.A. Cullen, and K.L. More (Oak Ridge National Laboratory); C. Galande and P.M. Ajayan (Rice University).

Funding for the Los Alamos work came from the DOE Office of Energy Efficiency and Renewable Energy through the Fuel Cell Technologies Office and from Los Alamos National Laboratory through the Laboratory Directed Research and Development (LDRD) program and a Director’s Postdoctoral Fellowship. The work was conducted in part at the Center for Integrated Nanotechnologies (CINT), a DOE Office of Science User Facility operated by Los Alamos National Laboratory and Sandia National Laboratories. The research supports the Lab’s Energy Security mission area and Materials for the Future science pillar.

Technical contact: Piotr Zelenay

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Showcased on the frontispiece of the journal’s communication section, this graphic combines schematic diagrams of a freestanding ozonated graphene oxide membrane and a hydrogen fuel cell operating with the membrane.