Fig. 1. Key operational challenges and characterization imperatives in CO2RR MEAs. (a) Schematic representation of the critical three-phase reaction interface (electrolyte, catalyst and CO2 gas) within an MEA, essential for efficient CO2 mass transport, electron/proton transfer, and catalytic conversion. (b) Catalyst degradation pathways: structural disintegration (e.g., detachment, dissolution) and agglomeration. (c) Interfacial failure mechanisms: flooding caused by interface hydrophobicity loss disrupts ionic conduction and gas/liquid transport, compromising MEA stability and product selectivity. (d) Heterogeneities in local microenvironment: local cation and pH gradients dynamically influence CO2 utilization, and reaction kinetics, impacting product selectivity and overall efficiency.

Fig. 2. In-situ and operando characterization techniques for resolving dynamic interfaces and degradation pathways in MEAs for CO2 electrocatalysis. (a) Complementary operando characterization techniques targeting key MEA components and processes: XAS/XAFS probes local catalyst structure and electronic state evolution through incident X-rays, detecting absorption edge shifts and white-line peak intensity changes in the reflected signal; Raman/FTIR interrogates interfacial reaction intermediates and local chemical environments via characteristic vibrational modes under incident optical excitation; MEA diagnosis tracks electrode potential distribution correlated with operating time to identify performance decay signatures; EIS and relaxation time analysis maps frequency-dependent impedance evolution to resolve charge transfer kinetics, ionic transport resistances, and transient degradation phenomena. Device photographs and detailed schematic diagrams of (b) operando X-ray absorption spectroscopy (XAS). (c) operando Raman spectroscopy and (d) MEA electrochemical diagnostics. (b) is reprinted with permission from Ref. [16]. Copyright 2024 American Chemical Society. (c) is reprinted with permission from Ref. [18]. Copyright 2024, American Chemical Society. (d) is reprinted with permission from Ref. [23]. Copyright 2020, American Chemical Society.

Fig. 3. Schematic representation of multimodal operando characterization strategies for resolving dynamic interfaces and degradation pathways in CO2RR MEA. This illustration maps key spatial regions within an MEA—electrolyte, catalyst layer, and GDL—to targeted diagnostic techniques. By integrating these spatially and temporally complementary techniques, future research will decode the interplay between catalyst dynamics, interfacial reactivity, and degradation cascades across hierarchical MEA structures under industrial operating conditions.