Unraveling the Role of Lithium-Ion Promotion in Iridium and Platinum Catalysts for CO Oxidation

The overreliance on fossil fuels has significantly exacerbated environmental issues, particularly the emission of harmful gases like carbon monoxide (CO), a byproduct of incomplete combustion [1]. CO oxidation, a widely studied catalytic process, converts CO into less harmful CO₂, presenting an energy-efficient approach to mitigate its adverse effects [2]. Nanostructured metals are commonly used as catalysts to facilitate this conversion process. Noble metals, such as Pt and Ir, supported on various oxides, are frequently employed to enhance the efficiency and stability of this reaction, leveraging metal-support interactions [3]. Electrochemical Promotion of Catalysis (EPOC) introduces a groundbreaking approach to dynamically enhance catalytic activity by applying an external electrical potential or current across solid electrolyte-supported catalysts. This non-Faradaic phenomenon arises from the migration of ionic species—such as alkali, oxygen, or lithium ions—from the electrolyte to the catalyst surface. This migration forms a neutral double layer that alters the work function and surface electronic properties of the catalyst, significantly influencing adsorption energies and reaction rates [4]. EPOC enables reversible and in-situ tuning of catalytic performance, offering immense potential for energy conversion, pollutant abatement, and chemical synthesis. Many traditional EPOC studies rely on solid electrolytes like YSZ or β''-Al 2 O 3 , which exhibit limitations at low temperatures, necessitating the exploration of alternative materials. In this work, we utilize Lithium lanthanum titanate (LLTO), with the chemical formula: La 2/3−x Li 3x TiO 3 , a perovskite-type solid electrolyte known for its high ionic conductivity and stability. LLTO demonstrates remarkable ionic conductivity, with values exceeding 10⁻³ S/cm at ambient temperature [5][6]. Additionally, it demonstrates excellent stability against moisture and high temperatures, making it ideal for practical applications [7][8]. Pt and Ir nanoparticles, synthesized using a modified polyol method, are deposited on LLTO to investigate their catalytic performance under varying electrochemical potentials and reaction conditions. This approach aims to provide insights into the role of Li-ion in Ir and Pt catalysts. The EPOC experiments conducted on Ir/LLTO achieved over 25% enhancement in reaction rate at 150°C under a negative potential (Fig.1), contrary to Pt/LLTO where the reaction rate decreased under the negative potential (Fig.2). Cyclic voltammetry is used for electrochemical characterization to deliver in situ information about the electrochemical interactions Additional physicochemical characterizations, including X-ray photoelectron spectroscopy (XPS), Energy Dispersive X-ray Spectroscopy (EDX), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM), will be employed to confirm the catalyst morphology, changes in metal oxidation states, and possible Li + migration under polarization. This research underscores the broad applicability of LLTO in EPOC studies and elucidates the distinct roles that Li-ion plays in various catalysts. References: [1] S. Dey, G. C. Dhal, D. Mohan, and R. Prasad, “Kinetics of catalytic oxidation of carbon monoxide over CuMnAgOx catalyst,” Materials Discovery , vol. 8, pp. 18–25, Jun. 2017, doi: 10.1016/j.md.2017.09.001. [2] C. Paris et al. , “Benefit of LDH-Derived Mixed Oxides for the Co-Oxidation of Toluene and CO Exhausted from Biomass Combustion,” Catalysts , vol. 14, no. 7, Jul. 2024, doi: 10.3390/catal14070455. [3] C. Panaritis, S. Yan, M. Couillard, and E. A. Baranova, “Electrochemical study of the metal-support interaction between FeOx nanoparticles and cobalt oxide support for the reverse water gas shift reaction,” Journal of CO2 Utilization , vol. 56, p. 101824, 2021, doi: 10.1016/j.jcou.2021.101824. [4] P. Vernoux et al. , “Ionically conducting ceramics as active catalyst supports,” Oct. 09, 2013, American Chemical Society . doi: 10.1021/cr4000336. [5] F. Huang, W. Liu, P. Li, J. Ning, and Q. Wei, “Electrochemical properties of LLTO/fluoropolymer-shell cellulose-core fibrous membrane for separator of high performance lithium-ion battery,” Materials , vol. 9, no. 2, 2016, doi: 10.3390/ma9020075. [6] S. Yan et al. , “Perovskite solid-state electrolytes for Lithium metal batteries,” Batteries , vol. 7, no. 4, 2021, doi: 10.3390/batteries7040075. [7] A. Okos, C. F. Ciobota, A. M. Motoc, and R. R. Piticescu, “Review on Synthesis and Properties of Lithium Lanthanum Titanate,” Nov. 01, 2023, Multidisciplinary Digital Publishing Institute (MDPI) . doi: 10.3390/ma16227088. [8] C. Bohnke, H. Duroy, and J. L. Fourquet, “pH sensors with lithium lanthanum titanate sensitive material: Applications in food industry,” Sens Actuators B Chem , vol. 89, no. 3, pp. 240–247, 2003, doi: 10.1016/S0925-4005(02)00473-2. Figure 1