Ionic-Liquid-Modified Electrocatalysts: From Surface Science to Spectroelectrochemistry
Solid State and Surface Chemistry, Material Synthesis
Final Report Abstract
The unique physicochemical properties of ionic liquids (ILs) have inspired the development of new concepts in catalysis, such as the Solid Catalyst with Ionic Liquid Layer (SCILL). In this approach, the IL is employed as a designer modifier to enhance the selectivity. In this project, it was explored whether this concept, which is successfully applied in heterogeneous catalysis, can be transferred to electrocatalysis. In specific, the project aimed at understanding the potential of electrochemical SCILLs in selective electrooxidation and electroreduction of hydrocarbon oxygenates. The mechanism of IL‐induced selectivity enhancement was explored at the molecular level combining a surface science approach in ultrahigh vacuum (UHV) with electrochemical studies using in‐situ spectroelectrochemical methods. In UHV, the interaction mechanisms of ILs were explored both with ordered noble metal surfaces (Pt(111) and Pd(111)) and with supported nanoparticles (Pt and Pd). The supported particle systems were prepared and characterized under UHV conditions. Infrared reflection absorption spectroscopy (IRAS) was used along with x‐ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM) and temperature programmed desorption (TPD). Detailed information was obtained on the site selectivity, adsorption geometry and interaction strength of several ILs on the model catalyst surfaces. The interaction of the ILs with coadsorbates was tested using CO as a probe molecule. These experiments provided information on the interaction strength with the surface, on the growth and wetting behavior, and in the transmission of reactants through the IL film. In the second part, the UHV studies were connected to in‐situ studies under electrochemical conditions using electrochemical IR spectroscopy (EC‐IRRAS), differential electrochemical mass spectrometry (DEMS), and electrochemical scanning tunneling microscopy (EC‐STM) along with other in‐situ methods. In a first step, the transfer procedures and the stability of the model catalysts was investigated in the electrochemical environment. It was shown that the model catalysts can be transferred from UHV into the electrochemical environment without major changes of the surface structure. In a second step, several test reactions were studied in the electrochemical environment both in the absence and in the presence of ILs. Both selective electrocatalytic hydrogenation (reduction) reactions and dehydrogenation (oxidation) reactions were explored. For the selective electrooxidation of secondary dioles, it was demonstrated for the first time that it is indeed possible to control the selectivity of an electrocatalytic transformation by addition of an IL as catalytic modifier. The observation could be explained on the basis of the potential dependent adsorption behavior of the IL on the Pt electrode surface. With increasing potential, the anions of the IL adsorb specifically on the electrode surface, as observed by EC‐IRRAS. As a result, OH groups are replaced from the surface which are essential reactants in the electrooxidation. By controlling the availability of the surface OH groups via the IL concentration it was possible to suppress specific oxidation steps and, thereby, drastically enhance the selectivity to a partial oxidation product. These findings demonstrate that it is indeed possible to use electrochemical SCILLs to control the selectivity of selective electrocatalytic transformations.
Publications
- Dynamic CO Adsorption and Desorption Through the Ionic Liquid Layer of a Pt Model SCILL, J. Phys. Chem. C 123, 31057 (2019)
C. Schuschke, C. Hohner, C. Stumm, M. Kettner, L. Fromm, A. Görling, J. Libuda
(See online at https://doi.org/10.1021/acs.jpcc.9b09128) - Cobalt Oxide‐Supported Pt Electrocatalysts: Intimate Correlation between Particle Size, Electronic Metal Support Interaction and Stability, J. Phys. Chem. Lett. 11, 8365 (2020)
M. Bertram, C. Prössl, M. Ronovský, J. Knöppel, P. Matvija, L. Fusek, T. Skála, N. Tsud, M. Kastenmeier, V. Matolín, K. Mayrhofer, V. Johánek, J. Mysliveček, S. Cherevko, Y. Lykhach, O. Brummel, J. Libuda
(See online at https://doi.org/10.1021/acs.jpclett.0c02233) - Electrifying Oxide Model Catalysis: Complex Electrodes based on Atomically‐Defined Oxide Films, Catal. Lett., 150, 1546 (2020)
O. Brummel, J. Libuda
(See online at https://doi.org/10.1007/s10562-019-03078-x) - Secondary Alcohols as Rechargeable Electrofuels: Electrooxidation of 2‐Propanol at Pt Electrodes, ACS Catal. 10, 6381 (2020)
F. Waidhas, S. Haschke, P. Khanipour, L. Fromm, A. Görling, J. Bachmann, I. Katsounaros, K.J.J. Mayrhofer, O. Brummel, J. Libuda
(See online at https://doi.org/10.1021/acscatal.0c00818) - Selective Electrooxidation of 2‐Propanol on Pt Nanoparticles Supported on Co3O4: An In‐situ Study on Atomically Defined Model Systems, J. Phys. D: Appl. Phys., 54, 164002 (2021)
T. Yang, M. Kastenmeier, M. Ronovský, L. Fusek, T. Skála, F. Waidhas, M. Bertram, N. Tsud, P. Matvija, K.C. Prince, V. Matolín, Z. Liu, V. Johánek, J. Mysliveček, Y. Lykhach, O. Brummel, J. Libuda
(See online at https://doi.org/10.1088/1361-6463/abd9ea) - Structural Dynamics of Ultrathin Cobalt Oxide Nanoislands under Potential Control, Adv. Funct. Mater.
C. Stumm, M. Bertram, M. Kastenmeier, F. D. Speck, Z. Sun, J. Rodrigez‐Fernandez, J.V. Lauritsen, K. J.J. Mayrhofer, S. Cherevko, O. Brummel, J. Libuda
(See online at https://doi.org/10.1002/adfm.202009923)
