Isomeric Cu(I) Azolate Frameworks Showing Contrasting Electrocatalytic CO₂ Reduction Selectivities and Stabilities

Metal‒organic frameworks have attracted wide interest in the electrocatalytic CO₂ reduction reaction (eCO₂RR), but their differences of performances originated from chemical composition and stabilities are rarely concerned. Here, isomeric Cu(I) triazolate frameworks (MAF-2Fa and MAF-2Fb) with similar thermal/chemical stabilities but very different coordination modes are used for eCO₂RR studies. MAF-2Fa with monotypic planar dinuclear Cu(I) coordination mode achieves high selectivity for C₂H₄ (53%) and C₂ products (70%), with almost unchanged over a wide potential window (‒1.1 to ‒1.5 V), making it among one of the best Cu-complex electrocatalysts. In contrast, MAF-2Fb with multiple Cu(I) coordination modes (including planar/bent dinuclear, linear mononuclear, and trigonal mononuclear ones) showed low C₂/C₁ products without significant differences. More interestingly, MAF-2Fa can maintain its performance for at least 8 h, whereas MAF-2Fb decomposed into inorganics with inferior performance after 1.5 h. The significant differences of eCO₂RR selectivities and stabilities are elucidated by computational simulations and operando electrochemical tests.