In-Situ Liquid Phase Transmission Electron Microscopy and Electron Diffraction Provides Mechanistic Insight into Electrochemical CO2 Reduction on Palladium/Palladium Hydride Catalysts

Electrochemical conversion of CO2 (CO2R) offers a sustainable route for producing fuels and chemicals. Pd-based catalysts are effective for selective conversion of CO2 into formate at low overpotentials and CO/H2 at high overpotentials. Furthermore, Pd catalysts undergo morphology and phase structure transformations under reaction conditions that are not well understood. Herein, in-situ liquid phase transmission electron microscopy (LP-TEM) and select area diffraction (SAD) measurements under CO2R conditions is applied to track the morphology and Pd/PdHx phase interconversion as a function of electrode potential, respectively. Correlating in-situ characterization with electrochemical CO2R activity/selectivity measurements, density functional theory and micro-kinetic analyses, the change in Pd/PdHx catalyst selectivity from formate at low overpotentials towards CO/H2 at higher overpotentials is found to result from electrode potential-dependent thermodynamic changes in the reaction energetics and not morphological or phase structure changes, providing insight that can guide advanced understanding and design of improved performance catalysts

Impact of palladium/palladium hydride conversion on electrochemical CO2 reduction via in-situ transmission electron microscopy and diffraction

Abstract Electrochemical conversion of CO2 offers a sustainable route for producing fuels and chemicals. Pd-based catalysts are effective for converting CO2 into formate at low overpotentials and CO/H2 at high overpotentials, while undergoing poorly understood morphology and phase structure transformations under reaction conditions that impact performance. Herein, in-situ liquid-phase transmission electron microscopy and select area diffraction measurements are applied to track the morphology and Pd/PdHx phase interconversion under reaction conditions as a function of electrode potential. These studies identify the degradation mechanisms, including poisoning and physical structure changes, occurring in PdHx/Pd electrodes. Constant potential density functional theory calculations are used to probe the reaction mechanisms occurring on the PdHx structures observed under reaction conditions. Microkinetic modeling reveals that the intercalation of *H into Pd is essential for formate production. However, the change in electrochemical CO2 conversion selectivity away from formate and towards CO/H2 at increasing overpotentials is due to electrode potential dependent changes in the reaction energetics and not a consequence of morphology or phase structure changes

Impact of palladium/palladium hydride conversion on electrochemical CO₂ reduction via in-situ transmission electron microscopy and diffraction

Electrochemical conversion of CO2 offers a sustainable route for producing fuels and chemicals. Pd-based catalysts are effective for converting CO2 into formate at low overpotentials and CO/H2 at high overpotentials, while undergoing poorly understood morphology and phase structure transformations under reaction conditions that impact performance. Herein, in-situ liquid-phase transmission electron microscopy and select area diffraction measurements are applied to track the morphology and Pd/PdHx phase interconversion under reaction conditions as a function of electrode potential. These studies identify the degradation mechanisms, including poisoning and physical structure changes, occurring in PdHx/Pd electrodes. Constant potential density functional theory calculations are used to probe the reaction mechanisms occurring on the PdHx structures observed under reaction conditions. Microkinetic modeling reveals that the intercalation of *H into Pd is essential for formate production. However, the change in electrochemical CO2 conversion selectivity away from formate and towards CO/H2 at increasing overpotentials is due to electrode potential dependent changes in the reaction energetics and not a consequence of morphology or phase structure changes.</p