Operando Surface Characterization on Catalytic and Energy Materials from Single Crystals to Nanoparticles

Abstract

Modern surface science faces two major challenges, a materials gap and a pressure gap. While studies on single crystal surface in ultrahigh vacuum have uncovered the atomic and electronic structures of the surface, the materials and environmental conditions of commercial catalysis are much more complicated, both in the structure of the materials and in the accessible pressure range of analysis instruments. Model systems and operando surface techniques have been developed to bridge these gaps. In this Review, we highlight the current trends in the development of the surface characterization techniques and methodologies in more realistic environments, with emphasis on recent research efforts at the Korea Advanced Institute of Science and Technology. We show principles and applications of the microscopic and spectroscopic surface techniques at ambient pressure that were used for the characterization of atomic structure, electronic structure, charge transport, and the mechanical properties of catalytic and energy materials. Ambient pressure scanning tunneling microscopy and X-ray photoelectron spectroscopy allow us to observe the surface restructuring that occurs during oxidation, reduction, and catalytic processes. In addition, we introduce the ambient pressure atomic force microscopy that revealed the morphological, mechanical, and charge transport properties that occur during the catalytic and energy conversion processes. Hot electron detection enables the monitoring of catalytic reactions and electronic excitations on the surface. Overall, the information on the nature of catalytic reactions obtained with operando spectroscopic and microscopic techniques may bring breakthroughs in some of the global energy and environmental problems the world is facing.

Single-Atom (Iron-Based) Catalysts: Synthesis and Applications

“…For the synthesis of Fe-SACs, Fe anchored by four N atoms appears to be the ideal chemical species for wider applications such as organic transformations, electrocatalysis under varying pH conditions, environmental remediation, N 2 fixation, and in battery and fuel cell operations . Various supports namely porous carbon, graphene, and C 3 N 4 have been utilized for the preparation of SACs, and modern analytical techniques such as XAFS, HAADF-STEM, and XPS enable the identification of the chemical state of SA metal sites on assorted supports, thus verifying the existence of SA. ,− The catalytic activity and selectivity of any catalytic processes could be tuned by selecting suitable support . The atomically dispersed nature of SACs allows the utilization of almost 100% of its activity, which bodes well for newer opportunities in several applications.…”

Heterogeneous Catalysis: Enabling a Sustainable Future

“…In the past, catalyst characterization was conducted "off-line" from the reaction environment, preventing physical insights from studying catalytic systems under practical conditions. We saw in the last decade a rapid development of in situ/operando characterization tools, which helped researchers to identify the catalyst descriptors and structure-reactivity relations (Choi et al, 2020). As the in situ/operando characterization tools become more sophisticated and functional under harsh conditions, e.g., high temperature and high pressure, we shall see a quantum leap in our ability to unlock many new catalysts and catalytic routes.…”

Celebrating 50 Years of KAIST: Collective Intelligence and Innovation for Confronting Contemporary Issues

“…In the third thrust, Prof. Jeong Yeong Park discusses the state-of-the-art in operando surface characterization techniques for studying a wide variety of chemical reactions on active materials in real, nonideal environments, which may help to uncover previously unidentified chemical reaction mechanisms (Figure 5a). 9 Conventional ex situ surface characterization techniques were limited to highly crystalline samples and ultrahigh vacuum (UHV), inevitably leaving gaps in our understanding of the surface chemistry of catalysts in their operational environment. To this end, ambient-pressure (AP) techniques, such as AP-STM (scanning tunneling microscopy), AP-XPS (X-ray photoelectron spectroscopy), AP-AFM (atomic force microscopy), vibrational spectroscopies, and E-TEM (environmental transmission electron microscopy), have been developed to characterize single crystal and nanoparticle samples in operando and to monitor previously unobservable chemical reactions that occur only in ambient temperature/pressures.…”

“…In the third thrust, Prof. Jeong Yeong Park discusses the state-of-the-art in operando surface characterization techniques for studying a wide variety of chemical reactions on active materials in real, nonideal environments, which may help to uncover previously unidentified chemical reaction mechanisms (Figure a) . Conventional ex situ surface characterization techniques were limited to highly crystalline samples and ultrahigh vacuum (UHV), inevitably leaving gaps in our understanding of the surface chemistry of catalysts in their operational environment.…”

“…Overview of the third thrust on advanced techniques in materials research. (a) Plot highlighting the so-called “pressure and material gaps” that exist between conventional characterization techniques that require high vacuum and practical applications in ambient settings, stressing the importance of operando tools to bridge this gap . (b) Schematic illustration highlighting the different stages of the development of graphene liquid cell (GLC) technology and their applications .…”