Operando synchrotron radiation insights into multiscale regulation of CO ₂ electroreduction

Electrochemical CO₂ reduction (CO₂RR) represents a promising approach toward sustainable carbon utilization, yet achieving high selectivity and stability in electrocatalysts requires precise control over their active-site structure, interfacial properties, and local reaction environment. Since these factors are subject to continuous evolution under operating conditions, advanced characterization techniques with adequate spatiotemporal and energy resolution are essential to establish reliable structure-performance correlations. Here, we present a systematic review of multiscale catalyst regulation strategies for CO₂RR, with particular emphasis on the role of operando synchrotron radiation (SR) techniques in elucidating the underlying reaction dynamics mechanisms. The discussion covers three interconnected dimensions, namely size effects, interface engineering and microenvironment modulation. For each dimension, we examine how tailored synchrotron-based spectroscopic and scattering methods can be employed to address the corresponding mechanistic questions. Particular attention is given to distinguishing reversible dynamic restructuring from irreversible degradation and to decoupling the interplay between intrinsic catalyst properties and the local reaction environment. We further discuss how operando SR characterizations can help resolve device-level challenges such as carbonate formation and mass transport limitations in membrane electrode assemblies. Finally, current technical limitations and emerging opportunities in synchrotron methodology are outlined to provide guidance for the future development of efficient CO₂RR systems.