Restructuring of Porphyrin Networks Driven by Self-Assembled Octanoic Acid Monolayer on Au(111)

Interfacial Engineering of Mn Porphyrin/Au Electrodes for Identifying MnOx as the Active Species under Oxygen Evolution Reactions

Understanding the influence of surface structural features at a molecular level is beneficial in guiding an electrode's mechanistic proposals for electrocatalytic reactions. The relationship between structural stability and catalytic activity significantly impacts reaction performance, even though atomistic knowledge of active sites remains a topic of discussion. In this context, this work presents scanning tunneling microscopy (STM) results for the highly ordered arrangement of manganese porphyrin molecules on a Au(111) surface; STM allows us to monitor active sites at a molecular level to focus on long-standing issues with the electrocatalytic process, especially the exact nature of the real active sites at the interfaces. After water oxidation, manganese porphyrin rapidly decomposes into active catalytic species as bright protrusions. These newly formed active species drastically lost catalytic activity, up to 82%, through only acid treatment, one of the oxide removal methods, not by deionized water and acetone treatments. STM results of the obviated active species on the Au surface by an acidic solution support the forfeited catalytic activity. In addition, it shows a 67% decrement in catalytic activity by adsorption of phosphonic acid, one of the oxide's preferred adsorption materials, compared to the pristine one. Based on these observations, we confirm that the newly formed active species, as water oxidation catalysts, mostly consist of manganese oxides. Notable findings of our work provide molecular evidence for the active sites of Au and modified Au electrodes that spur the future development of water oxidation catalysts.

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

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.