High-Sensitivity Low-Energy Ion Scattering Spectrometer will be a transformative resource for materials research at CU Boulder

Anonymous — Fri, 01 Apr 2022 06:00:00 +0000

High-Sensitivity Low-Energy Ion Scattering Spectrometer will be a transformative resource for materials research at CU Boulder Anonymous (not verified) Fri, 04/01/2022 - 00:00

Jonathan Raab

The HS-LEIS system in the SEEL building on East Campus.

CU Boulder’s East Campus is now home to the High-Sensitivity Low-Energy Ion Scattering (HS-LEIS) Spectrometer, a tool researchers from across the Rocky Mountain region will use for advanced materials characterization and analysis.

Because materials interact with the environment through their surfaces, knowledge of surface properties is critical to understanding structure-function relationships of existing and bespoke, next-generation materials designed for a variety of electronic, optical, biological, chemical and other applications, including functional coatings, photovoltaics, catalysis and more.

Housed in the Sustainability, Energy and Environment Laboratory building on East Campus, the HS-LEIS is the culmination of recent advances in detector design for surface analysis. The device can provide the most sensitive and selective methods for non-destructive, property-dictating, top-atomic-layer surface composition analysis.

“Coupled to this dual instrument system are several sample environments, such that one can expose materials to reactive atmospheres, high temperatures, electrochemical potential and other environments to examine their effect on the surfaces,” said Assistant Professor Adam Holewinski, the lead principal investigator of a team of five researchers who submitted the proposal to bring the instrument to CU Boulder. “This has turned into a rather unique, customized surface analysis platform with broad applicability.”

The HS-LEIS is currently the only device of its kind in the Rocky Mountain region, and only the second in the U.S. It is also unique in that it is complimented by an X-ray photoelectron spectroscopy system, to which it is physically tethered to perform sequential analysis on samples, as well as its unique complement of electrochemical cells. The platform also allows for interfaces with a glass reaction chamber that can reach temperatures up to 1200 degrees Celsius and handle corrosive and reactive gases.

Massimo Ruzzene, the associate dean for research in the College of Engineering and Applied Science, said materials research is and continues to be a strength of our college and the university as a whole.

“This instrument will be a new cornerstone in that area and my hope is it will spur exciting interdisciplinary research efforts on campus and in the region for years to come,” he said.

The acquisition of the HS-LEIS was made possible through a collaborative effort by a group of materials-focused researchers from the Department of Chemical and Biological Engineering, the Department of Chemistry, the Materials Science and Engineering Program and the Renewable and Sustainable Energy Institute. In 2019, co-principal investigators Tanja Cuk, Steve George, Adam Holewinski, Mike McGehee and Will Medlin developed a proposal that they submitted to the National Science Foundation, which ultimately funded the creation of the platform.

The HS-LEIS will be accessible to CU Boulder researchers and those in academia and industry. For more information, please contact Adam Holewinski.

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Cuk Research Group isolates reaction step that describes energetics of catalysis on materials

Anonymous — Thu, 16 Dec 2021 16:39:49 +0000

Cuk Research Group isolates reaction step that describes energetics of catalysis on materials Anonymous (not verified) Thu, 12/16/2021 - 09:39

Jonathan Raab

Associate Professor Tanja Cuk

New research published in Nature Materials from Associate Professor Tanja Cuk and colleagues sheds light on a fundamental chemical reaction — the breaking apart of water to produce a molecular fuel such as hydrogen. Cuk is faculty in the Department of Chemistry and the Materials Science and Engineering Program (MSE) and is a Fellow in the Renewable and Sustainable Energy Institute (RASEI).

When water undergoes such a reaction, there are a number of discrete reaction steps that should occur in sequence. Cuk’s lab specializes in timing these steps and therefore isolating individual reactions as part of the broader process.

“This paper isolated one of the reaction steps in time, so we can then learn more about the energetics of that discrete step — how strong or weak the bonds are before and after it — within the broader reaction,” Cuk said.

Understanding the free energy needed to form a chemical is key to its usefulness as a fuel source. If an element has weak electrochemical bonds, it has a high-energy potential, because it can be broken apart easily.

“Similar to what plants do naturally, we are trying to break the bonds of water and reform the bonds of oxygen,” Cuk said. “The protons left over create hydrogen for fuel.”

Cuk and her group used a pulsing photovoltaic effect to generate current and a tuning of the water’s pH to get more products of the first step — reaction intermediates — with higher pH. This creates a curve — the reaction isotherm of Figure 4 in the manuscript and depicted in Figure 1, right — from which the free energy change of that reaction step can be determined.

Figure 1. The time-resolved optical data as a function of pH (litmus scale on the bottom) show how the population of intermediates generates a reaction isotherm (black trace). The emission (in blue) counts the intermediate population (cartooned) and from its growth, one obtains the free energy change for the first electron transfer from water. Figure constructed with the aid of Daniel Morton of RASEI.

“The electrochemical reaction was driven by the charge,” Cuk said. “We have an electrode and we shine light on it. That is the energy inputted into the whole reaction. But we shine pulsed light, so we can time the separate reaction steps within the total fuel-producing reaction.”

Because sunlight is continuous, it can obscure the individual steps associated with a chemical reaction. Using pulsed light in principle allows the researchers to experimentally determine the free energy needed for each meta-stable reaction step. However, a pulsed light spectroscopy, usually called pump-probe or time-resolved spectroscopy, had yet to live up to this.

This work experimentally determined the free energy change of the first electron and proton transfer from water at a material surface. This understanding is especially important for materials science because theorists use it to differentiate the activity of water splitting catalysts. If this is a difficult, energy-intensive process, the catalyst is not as efficient at producing the final fuel, hydrogen.

Ilya Vinogradov, a postdoctoral researcher in the Cuk Research Group and with RASEI, contributed to building the transient reflectance setup, wrote new data acquisition software and mentored the graduate students in data acquisition and analysis. MSE graduate students Suryansh Suryansh and Hanna Lyle acquired the data and processed the data sets. Michael Paolino, a graduate student in Physics, aided in the latest data collection. Vinogradov furthered the SVD analysis spearheaded by Research Associate Aritra Mandal and contributed to the rotation analysis described in Figure 2.

“This research is impactful because it provides an experimental measure of an important theoretical materials performance predictor — free energy change of the first electron transfer step — for water splitting catalysis,” Vinogradov said. “If a material’s descriptor correlates well with device performance, one can computationally optimize its chemical composition and crystal structure for the descriptor in lieu of directly measuring the device’s performance.”

This allows researchers to evaluate different materials as high performers more efficiently and quickly, saving time and cost for materials that would otherwise need to be subject to experimentation.

“Although our method is not quite there yet in terms of throughput and precision, one way a more solid experimental footing may help improve the materials design strategy is by discovering non-idealities that the theorists may have missed,” Vinogradov said. “This can help improve the descriptor's predictive accuracy.”

Cuk said some of these non-idealities would have to do with the reaction kinetics, or the timing with which the intermediate products turn over, rather than directly with the free energies of each reaction step.

“This is important for a truly sustainable energy storage cycle, where the rate at which products turnover keeps up with the rate at which rays of sunlight come in,” she said. “By using a time-resolved spectroscopy, we can get at both the free energies and the rates that circumscribe fuel production.”

New research published in Nature Materials from Associate Professor Tanja Cuk and colleagues sheds light on a fundamental chemical reaction — the breaking apart of water to produce a molecular fuel such as hydrogen. Cuk is faculty in the Department of Chemistry and the Materials Science and Engineering Program (MSE) and is a Fellow in the Renewable and Sustainable Energy Institute (RASEI).

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