Operando Spectroscopic Platforms for Probing Catalyst Behavior under Realistic Electrochemical and Photocatalytic Environments

Sung-Fu Hung (洪崧富)

National Yang Ming Chiao Tung University Department of Applied Chemistry (國立陽明交通大學 應用化學系)

Abstract:

Electrochemical environments in different reactor configurations can lead to markedly distinct catalytic behaviors. For CO2 reduction reaction (CO2RR), flow-based reactors have demonstrated substantial improvements in Faradaic efficiency and catalytic current density compared with conventional H-type cells.[1] These differences highlight the unique microenvironment and catalytic characteristics of flow-cell systems.
To accurately evaluate the intrinsic properties of catalysts under realistic flow-cell operating conditions, custom-designed flow cells have been specifically devised for operando X-ray absorption spectroscopy (XAS) [2,3] and operando Raman spectroscopy [4,5] during CO2RR. These systems avoid the limitations of conventional in situ measurements performed in three-electrode H-cells, where the catalytic environment differs significantly from that of practical electrochemical measurements. Such operando configurations ensure that spectroscopic observations are obtained under conditions consistent with actual catalytic performance testing.
Another important flow-based configuration, the membrane electrode assembly (MEA), also exhibits catalytic behavior distinct from both flow cells and H-cells. Accordingly, operando MEA reactors have been designed for XAS measurements to investigate catalyst evolution and reaction behavior during CO₂RR and proton-exchange-membrane water splitting.
For second-row transition metals, the intrinsic spectral resolution of conventional XAS can limit the ability to resolve subtle operando changes during catalysis. To overcome this challenge, operando high-resolution fluorescence-detected XAS has been developed to detect and identify fine spectral variations associated with catalytic processes.[6]
Beyond electrocatalysis, solar irradiation can also be used to drive photocatalytic reactions by introducing gaseous reactants to catalyst surfaces. An electrolyte-free operando photocatalytic system has therefore been developed to monitor catalyst evolution under realistic photocatalytic conditions.[7]
Overall, operando spectroscopic techniques provide critical insights into catalytic current density, chemical states, crystal structures, and reaction intermediates. Such comprehensive understanding of catalyst behavior across diverse reaction systems is essential for guiding the development of advanced catalytic technologies toward Net Zero emissions.