Summer Scholar Alexandra Barth analyzes carbon monoxide resistance of core-shell nanoparticle catalysts in the Román Lab.
|MPC-CMSE Summer Scholar Alexandra Barth works at a hood where she makes carbide core-platinum shell nanoparticles for electrocatalytic applications such as fuel cells and electrolyzers in the lab of MIT Associate Professor of Chemical Engineering Yuriy Román-Leshkov. The process of making core-shell nanoparticles consists of many steps and takes three to five days to complete. Photo, Maria E. Aglietti, Materials Processing Center.|
In May the group of MIT Associate Professor of Chemical Engineering Yuriy Román-Leshkov published a study showing that an ultra-thin shell of platinum on a carbide core could catalyze hydrogen evolution and oxidation reactions as effectively as pure platinum at a fraction of the cost. MPC-CMSE Summer Scholar Alexandra T. Barth is helping to advance this work by studying the tunability of these core-shell materials and their performance in a number of electrocatalytic applications.
“What’s been interesting is we found even when we’re creating nanoparticles that are just coated with an atomically thin layer of platinum, they act as effectively as conventional platinum-only nanoparticle catalysts,” Barth explains.
Platinum is a key component in many traditional and emerging technologies, including automobile catalytic converters, oil reforming, fuel cells and electrolyzers. The goal of the project, Dr. Maria Milina, a postdoctoral associate in the Román group explains, is to design noble metal catalysts with significantly reduced metal loadings but improved activity and stability. “We tackle this challenge through the synthesis of core-shell nanoparticles, in which a cheap metal carbide core not only reduces the requirements for expensive platinum but also beneficially modifies its electronic properties,” says Milina.
Avoiding carbon monoxide poisoning
The research of Prof. Román shows that platinum-coated carbide nanoparticles can be used as catalysts for hydrogen evolution and hydrogen oxidation reactions that occur at the cathode of water electrolyzers and at the anode of fuel cells, respectively. Simultaneously they demonstrate remarkable resistance to carbon monoxide, a common catalyst poison. “You want to create a catalyst that will activate hydrogen even when carbon monoxide is present in fuel streams,” Barth says. Carbon monoxide is known to bind strongly to platinum and to block its ability to catalyze other reactions. “Metal carbide cores favorably modulate electronic properties of platinum through subsurface strain and ligand effect leading to the reduced carbon monoxide binding energy of platinum in a core-shell architecture,” explains Prof. Román.
Barth, a rising senior from Florida State University, is interning in the Román lab at MIT this summer. She is synthesizing core-shell nanoparticles with varying core and shell composition, examining their structure with techniques such as infrared spectroscopy and powder X-ray diffraction, and conducting electrocatalytic experiments to analyze their performance in hydrogen evolution/hydrogen oxidation reactions.
A multistep process
The process of making core-shell nanoparticles consists of many steps and takes three to five days to complete, Barth notes. “It’s interesting because the entire process was devised in this lab, so it’s like nothing that’s been done before,” she says. The process involves synthesizing the nanoparticles in a reverse microemulsion, heating the sample in a methane atmosphere to produce a carbide core, and separating the nanoparticles from their silica templates simultaneously dispersing them on a high surface area carbon support in a diluted hydrofluoric acid. The last step in the process, working with hydrofluoric acid, required special safety training.
After synthesis, Barth tests the core-shell nanoparticle catalyst in a three-electrode electrochemical cell. “We initially determine the hydrogen evolution and oxidation activity of the catalysts in a pure hydrogen atmosphere. Then we intentionally introduce carbon monoxide poison into the hydrogen stream and record how quickly catalyst deactivates and how high is the overpotential required to strip carbon monoxide from the platinum surface,” she says.
Infrared spectroscopy challenge
While characterization of solids by X-ray diffraction was a familiar skill from her work at FSU, Barth was facing a challenge with infrared spectroscopy. “We know what we’re expecting of this analysis. I firstly need to record a spectrum of a reduced in hydrogen catalyst, then I should saturate it with carbon monoxide and, after removal of physisorbed species, register another spectrum with the absorbances corresponding to platinum-carbon monoxide interactions. But the use of infrared spectroscopy for carbon-supported catalysts has been always a challenge due to the high opacity of these materials. So that’s been a work in progress,” she says.
“Back at FSU, I do radiochemistry research, so I make crystals with nuclear elements,” she explains. “This is out of my comfort zone because I’ve never done nanoparticle research before, and I’ve never done catalysis research before. But what I have realized through doing this summer project is that I could advance my current research at FSU by including new catalytic studies.” Barth is considering modifying her honors thesis to bridge radiochemistry and catalysis, taking her work from just making crystals to testing their catalytic properties.
Barth is pursuing a major in chemistry at Florida State and hopes to pursue a doctorate in inorganic chemistry.
MPC and CMSE sponsor the nine-week National Science Foundation Research Experience for Undergraduates (NSF REU) internships with support from NSF’s Materials Research Science and Engineering Centers program (grant number DMR-14-19807). The program runs from June 7 through Aug. 6, 2016.
– Denis Paiste, Materials Processing Center | July 27, 2016