Multiscale Regulation of Interfacial Microenvironments for High-Efficiency Electrochemical CO2 Reduction to C2+ Products: A Review and Perspective

Abstract Electrochemical reduction of CO2 to high-value C2+ products represents a promising route for achieving a sustainable carbon cycle, yet its practical application is hindered by intrinsic challenges in catalyst design, reaction pathways, and carbonate precipitation, which affect the efficiency, selectivity, safety, and lifespan of electrolyzers. This review systematically reorganizes the CO2-to-C2+ electrocatalysis literature around an explicit four-dimension × four-scale matrix (4D × 4S), where the four dimensions are materials engineering (I), confinement/tandem (II), microenvironment/interface regulation (III), and reactor/operation (IV), and the four scales are electronic structure, atomic-to-molecular reaction network, mesoscopic transport, and device-reactor performance. This review draws on representative experimental and computational studies in CO2-to-C2+ electrocatalysis rather than attempting an exhaustive catalog. We have the following main conclusions: (i) atomic-site design shall cooptimize with mesoscale confinement and microenvironment to achieve higher selectivity at industrial current densities; (ii) membrane-electrode-assembly lifetime, not peak performance, is the central bottleneck for C2+ commercialization, with salt precipitation and cation crossover as the dominant failure modes2; (iii) several material classes (atomically defined paired sites, conductive MOFs/COFs, etc.) can maintain high Faraday efficiency of their respective specific C2+ products at industrial current densities, but each faces a characteristic trade-off (e.g., lifetime vs. selectivity) that no single optimization strategy can resolve; (iv) Cross-scale theoretical–experimental closure, enabled by operando spectroscopy, machine-learning surrogates, and physics-informed neural networks, is the most promising direction for accelerating the field. The 4D × 4S matrix provides a reusable scaffold for designing and evaluating the next generation of C2+ electrocatalysts and electrolyzers, with standardized operando datasets and community-accepted validation protocols as the immediate priorities. We expect that CO2-to-CO will be the realistic first commercial target, with C2+ products as a longer-term goal contingent on substantial catalyst and membrane innovation.