Operando characterization technique innovations in single-atom catalyst-derived electrochemical CO₂ conversion

Single-atom catalysts (SACs) are the perfect epitome of cutting-edge innovation in catalysis, offering distinct active sites in the form of isolated, individual atoms. SACs amalgamate the advantages of homogeneous and heterogeneous catalysis, in turn enhancing the activity, selectivity, and stability during catalytic processes. The latest progressions in in situ/operando characterization techniques have simplified the understanding of the catalyst heterogeneity and structure sensitivity of SACs by enabling the real-time observation of SACs under a coexistent working environment to provide insights into their structure and catalytic efficiency. Operando techniques are the backbone for investigating the stability and activity of SACs during energy conversions. Techniques such as operando X-ray absorption spectroscopy (XAS), polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS), and near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) have been employed to study SACs under different reaction conditions. Furthermore, in situ visualization microscopy techniques have made notable progress in the imaging of ongoing catalytic reactions on SACs and revealed enigmatic effects such as facet-resolved catalytic ignition and anisotropic surface oxidation. Therefore, in this review, we have compiled the developments in the significant operando characterization techniques for SAC-derived electrochemical carbon dioxide reduction reaction (eCO₂RR).