Rice University chemists who developed a unique form of graphene have found a way to embed metallic nanoparticles that turn the material into a useful catalyst for fuel cells and other applications. Laser-induced graphene, created by the Rice lab of chemist James Tour last year, is a flexible film with a surface of porous graphene made by exposing a common plastic known as polyimide to a commercial laser-scribing beam. The researchers have now found a way to enhance the product with reactive metals. The research appears this month in the American Chemical Society journal ("In situ Formation of Metal Oxide Nanocrystals Embedded in Laser-Induced Graphene"). 
A scanning electron microscope image shows cobalt-infused metal oxide-laser induced graphene produced at Rice University. The material may be a suitable substitute for platinum or other expensive metals as catalysts for fuel cells. The scale bar equals 10 microns. (Image: Tour Group/Rice University) With the discovery, the material that the researchers call "metal oxide-laser induced graphene" (MO-LIG) becomes a new candidate to replace expensive metals like platinum in catalytic fuel-cell applications in which oxygen and hydrogen are converted to water and electricity. "The wonderful thing about this process is that we can use commercial polymers, with simple inexpensive metal salts added," Tour said. "We then subject them to the commercial laser scriber, which generates metal nanoparticles embedded in graphene. So much of the chemistry is done by the laser, which generates graphene in the open air at room temperature. "These composites, which have less than 1 percent metal, respond as 'super catalysts' for fuel-cell applications. Other methods to do this take far more steps and require expensive metals and expensive carbon precursors." Initially, the researchers made laser-induced graphene with commercially available polyimide sheets. Later, they infused liquid polyimide with boron to produce laser-induced graphene with a greatly increased capacity to store an electrical charge, which made it an effective supercapacitor. 
Rice University chemists embedded metallic nanoparticles into laser-induced graphene. The particles turn the material into a useful catalyst for fuel cell and other applications. (Image: Tour Group/Rice University) For the latest iteration, they mixed the liquid and one of three concentrations containing cobalt, iron or molybdenum metal salts. After condensing each mixture into a film, they treated it with an infrared laser and then heated it in argon gas for half an hour at 750 degrees Celsius. That process produced robust MO-LIGs with metallic, 10-nanometer particles spread evenly through the graphene. Tests showed their ability to catalyze oxygen reduction, an essential chemical reaction in fuel cells. Further doping of the material with sulfur allowed for hydrogen evolution, another catalytic process that converts water into hydrogen, Tour said. "Remarkably, simple treatment of the graphene-molybdenum oxides with sulfur, which converted the metal oxides to metal sulfides, afforded a hydrogen evolution reaction catalyst, underscoring the broad utility of this approach," he said.
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A scanning electron microscope image shows cobalt-infused metal oxide-laser induced graphene produced at Rice University. The material may be a suitable substitute for platinum or other expensive metals as catalysts for fuel cells. The scale bar equals 10 microns. (Image: Tour Group/Rice University) With the discovery, the material that the researchers call "metal oxide-laser induced graphene" (MO-LIG) becomes a new candidate to replace expensive metals like platinum in catalytic fuel-cell applications in which oxygen and hydrogen are converted to water and electricity. "The wonderful thing about this process is that we can use commercial polymers, with simple inexpensive metal salts added," Tour said. "We then subject them to the commercial laser scriber, which generates metal nanoparticles embedded in graphene. So much of the chemistry is done by the laser, which generates graphene in the open air at room temperature. "These composites, which have less than 1 percent metal, respond as 'super catalysts' for fuel-cell applications. Other methods to do this take far more steps and require expensive metals and expensive carbon precursors." Initially, the researchers made laser-induced graphene with commercially available polyimide sheets. Later, they infused liquid polyimide with boron to produce laser-induced graphene with a greatly increased capacity to store an electrical charge, which made it an effective supercapacitor. Rice University chemists embedded metallic nanoparticles into laser-induced graphene. The particles turn the material into a useful catalyst for fuel cell and other applications. (Image: Tour Group/Rice University) For the latest iteration, they mixed the liquid and one of three concentrations containing cobalt, iron or molybdenum metal salts. After condensing each mixture into a film, they treated it with an infrared laser and then heated it in argon gas for half an hour at 750 degrees Celsius. That process produced robust MO-LIGs with metallic, 10-nanometer particles spread evenly through the graphene. Tests showed their ability to catalyze oxygen reduction, an essential chemical reaction in fuel cells. Further doping of the material with sulfur allowed for hydrogen evolution, another catalytic process that converts water into hydrogen, Tour said. "Remarkably, simple treatment of the graphene-molybdenum oxides with sulfur, which converted the metal oxides to metal sulfides, afforded a hydrogen evolution reaction catalyst, underscoring the broad utility of this approach," he said.
The zipped (left) and unzipped (right) forms of the protein GCN4-p1passing through a pore are shown. The differences in shape between the dimer and monomer versions of the protein translate to changes in charge, which can be read by electronics surrounding the nanopore. (Inage: Jeffery Saven and Wenhao Liu) The study was led by Marija Drndic, a professor in the School of Arts & Sciences' Department of Physics & Astronomy; David Niedzwiecki, a postdoctoral researcher in her lab; and Jeffery G. Saven, a professor in Penn Arts & Sciences' Department of Chemistry. It was published in the journal ("Observing Changes in the Structure and Oligomerization State of a Helical Protein Dimer Using Solid-State Nanopores"). The Penn team's technique stems from Drndic's work on nanopore gene sequencing, which aims to distinguish the bases in a strand of DNA by the different percent of the aperture they each block as they pass through a nanoscopic pore. Different silhouettes allow different amounts of an ionic liquid to pass through. The change in ion flow is measured by electronics surrounding the pore; the peaks and valleys of that signal can be correlated to each base. While researchers work to increase the accuracy of these readings to useful levels, Drndic and her colleagues have experimented with applying the technique to other biological molecules and nanoscale structures. Collaborating with Saven's group, they set out to test their pores on even trickier biological molecules. "There are many proteins that are much smaller and harder to manipulate than a strand of DNA that we'd like to study," Saven said. "We're interested in learning about the structure of a given protein, such as whether it exists as a monomer, or combined with another copy into a dimer, or an aggregate of multiple copies known as an oligomer." Detection is also often a limitation. "There are no ways to amplify peptides and proteins like there are for DNA," Drndic said. "If you want to study proteins from a particular source, you're stuck with very small samples. With this method, however, you can just collect the amount of data you need and the number of proteins you want to pass through the pore and then study them one at a time as they naturally exist in the body." Using the Drndic group's silicon nitride nanopores, which can be drilled to custom diameters, the research team set out to test their technique on GCN4-p1, a protein selected because it contains a common structural motif found in transcription factors and intracellular receptors. "The dimer version is 'zipped' together," Niedzwiecki said, "It is a 'coiled coil' of interleaved helices that is roughly cylindrical. The monomer version is unzipped and is likely not helical; it's probably more like a string." The researchers put different ratios of zipped and unzipped versions of the protein in an ionic fluid and passed them through the pores. While unable to tell the difference between individual proteins, the researchers could perform this analysis on populations of the molecule. "The dimer and monomer form of the protein block a different number of ions, so we see a different drop in current when they go through the pore," Niedzwiecki said. "But we get a range of values for both, as not every molecular translocation event is the same." Determining whether a specific sample of these types of proteins are aggregating or not could be used to better understand the progression of disease. "Many researchers," Saven said, "have observed these long tangles of aggregated peptides and proteins in diseases like Alzheimer's and Parkinson's, but there is an increasing body of evidence that is suggesting these tangles are occurring after the fact, that what are really causing the problem are smaller protein assemblies. Figuring out what those assemblies are and how large they are is currently really hard to do, so this may be a way of solving that problem."