A Stereoscopic Perspective on the Triple-Phase Interface Microenvironment in Electrochemical CO2 Reduction: Insights from In Situ Studies

Abstract When powered by renewable electricity, the electrochemical carbon dioxide reduction reaction (CO 2 RR) represents a transformative strategy for achieving sustainable carbon–neutral cycles. Researchers are striving to decode its ambiguous mechanisms through in situ characterization and establish structure–activity correlations in CO 2 RR systems under operating conditions. Despite these efforts, building a coherent framework that connects insights into atomic-level processes to macroscopic system behavior remains challenging. From this perspective, we present a holistic overview of the critical microregions in CO 2 RR systems and the associated phenomena requiring scrutiny at the triple-phase interface from a stereoscopic perspective. We systematically summarize recent advances in in situ characterization techniques applied across the distinct microregions, including the electrolyte microenvironment, reaction interface, electrocatalyst structure, and diffusion field. By integrating these insights, we highlight advances in mapping the dynamic cross-compartment interactions and transient species formation mechanisms within the CO 2 RR process. Finally, we conclude with suggestions for future research, emphasizing the need for synergistic integration of in situ characterization tools and innovative methodologies to resolve lingering mechanistic ambiguities. Such advancements could accelerate the rational design of efficient CO 2 RR systems and development of sustainable energy solutions.