Scaling Low-Temperature CO ₂ -to-Syngas Electroreduction: Failure Modes, Engineering Bottlenecks, and Mitigation Strategies

Low-temperature CO2 electroreduction (CO2eR) to syngas offers tunable H2:CO ratios and a renewable route to decarbonized syngas production, yet catalyst-level advances rarely translate to scalable, durable systems. This review addresses that disconnect with a systems-engineering perspective. We first establish the component foundations, electrolytes, membranes, and cell architectures of flow cells and zero-gap membrane electrode assembly (MEA) electrolyzers, together with integrated versus decoupled syngas production modes, then analyze the engineering failure modes that dominate at scale: non-uniform current distribution, localized hotspots, electrode flooding, salt precipitation, and thermal gradients. Single-pass CO2 conversion efficiency (SPCE) is introduced as a co-equal metric alongside Faradaic and energy efficiency (FE/EE). Original contributions include a standardized accelerated stress test (AST) protocol, a lifecycle sustainability assessment (LCSA) framework with quantitative carbon footprint benchmarking, a mitigation strategy compatibility matrix, and three-benchmark design pathways targeting high EE, high stability, and high SPCE, providing a