Advanced STEM Imaging and Spectroscopy for Energy Conversion Materials and Device Research

Energy conversion devices will play a critical role in the transition to a sustainable future by enabling, for example, generation and utilization of green hydrogen [1,2]. Key to these devices are often catalytic materials supported on or within a host material to form a heterogeneous catalyst. Improving heterogeneous catalysts often requires understanding their structure, composition, and bonding environment down to the atomic scale, since properties at these length scales can dictate the performance and durability of the devices utilizing them. These properties can additionally vary across the length scales of the electrodes in which they are incorporated (microns or larger), making high-resolution characterization over large length scales necessary to fully understand relevant properties on the device scale. In addition, the atomic-scale structure of many next-generation heterogeneous catalysts, such as single-atom electrocatalysts (SAEs), is highly sensitive to the high-energy electron probes typically used to characterize materials at this scale, making accurate assessment of their native structure challenging. In each of these cases, characterization by conventional high-resolution (scanning) transmission electron microscopy ((S)TEM) is therefore insufficient to fully understand the properties of heterogeneous catalyst materials utilized in devices.<br/><br/>Here, we will discuss automated (S)TEM imaging and spectroscopy techniques that allow high-resolution information to be obtained and across large fields of view and/or large numbers of catalyst sites [3,4], which, when combined with statistical data analyses, allow the properties of heterogeneous catalyst materials to be more fully understood across relevant scales. In addition, we will discuss the use of ultra-low voltage electron ptychography, performed at 30 keV, to enable direct imaging of the native atomic-scale structure of single-atom electrocatalyst sites while minimizing structural modifications [5]. Combined, these techniques will enable a more accurate and complete picture of the properties of heterogeneous catalyst systems to be obtained, aiding in the development of more advanced materials and devices that are essential for a sustainable future.<br/> <br/>References:<br/>[1] K. Ayers et al., <i>Annu Rev Chem Biomol Eng</i> <b>10</b>, 219 (2019).<br/>[2] D.A. Cullen et al., <i>Nat Energy</i> <b>6</b>, 462 (2021).<br/>[3] H. Yu et al., <i>ACS Nano</i> <b>16</b>, 12083 (2022).<br/>[4] M.J. Zachman et al., <i>Electrochim Acta</i><b> 469</b>, 143205 (2023).<br/>[5] M.J. Zachman et al., <i>Microsc Microanal</i><b> 27</b> (Suppl 1), 2976 (2021).<br/> <br/>This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the Million Mile Fuel Cell Truck (M2FCT) Consortium, technology manager Greg Kleen, and the Electrocatalysis (ElectroCat) consortium, technology manager David Peterson. Electron microscopy research was supported by the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.