Speakers
Description
Electrocatalysts exist within a complex liquid reaction environment and experience (electro)chemical driving force that can change their structural and composition from the as-synthesized state. It is, therefore, crucial that we have insight into the working state of the catalyst if we are to reliably relate the catalyst morphologies with this associated catalytic performance. Even though this need to provide insight to inform the design of catalysts for various green energy applications has driven the widespread development and adoption of operando techniques, there remains a crucial gap because the current methods are either broad beam spectroscopy techniques that are mostly sensitive to the ensemble chemical signatures of the catalytic system or microscopic techniques that can provide high spatial resolution imaging of the catalyst morphology but limited information of the catalyst’s chemical state.
In this presentation, we will show how a synergistic combination of transmission electron microscopy (TEM) and transmission X-ray microscopy (TXM) using the same operando microscopy platforms allow us to interrogate both restructuring and chemical composition of identical catalysts under reaction conditions. The first example involves looking at the phase stability of Cu2O cubes under nitrate reduction (NO3RR) conditions. Our TEM results reveal that unlike the rapid restructuring previously reported for carbon dioxide electro-reduction1, the Cu2O cubes were able to maintain their structural integrity during NO3RR at moderately reductive potentials together with a slow formation of redeposited particles. TXM measurements performed with the same electrochemical cell holder at the U41-TXM beamline indicate that the cubes also do not experience rapid reduction, and the emergence of the metallic phase arises from the re-deposition and not reduction. This phase co-existence is further used to rationalize the active phase for ammonia formation2. In the next example, we applied the same approach to the study of oxidation state changes in the Co(OH)2 nanosheets under oxygen evolution (OER) conditions in the Fe impurity containing electrolyte. It is known that the presence of Fe drastically improves the OER activity of Co(OH)2 pre-catalysts but the exact mechanism remains under debate. Here, the TEM results show that the presence of Fe suppresses the degradation of the nanosheets during reaction while scanning TXM measurements at MYSTIIC beamline is used to reveal the oxidation states of the transformed pre-catalysts and the secondary particles formed3.
References:
1. Grosse, P. et al. Dynamic Transformation of Cubic Copper Catalysts during CO2 Electroreduction and its Impact on Catalytic Selectivity. Nat. Commun. 12, 6736 (2021).
2. Yoon, A. et al. Revealing Catalyst Restructuring and Composition During Nitrate Electroreduction through Correlated Operando Microscopy and Spectroscopy. Nat. Mater. Accepted (2024).
3. Yang, F. et al. Fe-Induced Stabilization of Co(OH)₂ Nanosheets: Unveiling Structural and Oxidation State Dynamics in Oxygen Evolution Reaction via Operando Microscopy and Spectroscopy. In Preparation (2024).
