Collaborative Research: High-resolution electrochemical and Correlated microscopic characterization of 2D electrocatalysts

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Professor Michael Mirkin of CUNY Queens College and Professor Huolin Xin of the University of California-Irvine are supported by the Chemical Catalysis Program of the Division of Chemistry to study two-dimensional materials, such as flat nanosheets of transition metal chalcogenides as electrocatalysts for speeding up the electrocatalytic production of hydrogen from water. The knowledge obtained is applicable to other important chemical reactions relevant to alternative energy production and storage technologies. The project seeks to develop a unique microscopy technique that allows for the high-resolution imaging of the reactive site. This imaging is conducted using two techniques: transmission electron microscopy (for atomic-scale structural information) and scanning electrochemical microscopy (for electrochemical information). Correlating the data of the two complementary techniques provides information on the nature of the catalytic nanosheet edges, defects and atomic steps. The information is needed to understand the catalytic activity of these materials. The project provides training for a diverse group of students in renewable energy related science and technology, including mathematical modeling and data processing and mining. Area middle school students are exposed to science research through hand-on experience in the investigators' laboratories. The overarching goal of this collaborative research is to visualize and quantify active sites on two-dimensional (2D) catalyst surfaces via high-resolution (i.e., equal or less than 10 nm) reactivity mapping by scanning electrochemical microscopy (SECM) in combination with scanning transmission electron microscopy (STEM) techniques. By using very small nanoelectrode probes and significantly increasing the SECM resolution the researchers map and quantitatively measure activities of the nanosheet edges, defects and atomic steps on 2D electrocatalysts and assess the effects of phase transformations and surface functionalization. The methodology is developed for multi-technique imaging of the same nanoscale portion of the catalytic surface to obtain spatially resolved mechanistic information about heterogeneous processes on 2D electrocatalysts. The nature of the active sites is elucidated by correlating the SECM activity maps with atomic scale structural and bonding information obtained by STEM and spatially resolved electron energy loss spectroscopy (STEM-EELS) with one-to-one correspondence. These approaches investigate two important classes of 2D materials - transition metal dichalcogenides and MXenes. The objective of the research project is to advance the understanding of factors influencing the activity/stability of 2D electrocatalysts and to help put forward new strategies for improving these properties.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.