Realizing Ampere-Level Electrochemical CO ₂ Reduction Using Gas Diffusion Electrodes

Electrochemical CO2 reduction (ECR) offers a promising pathway to convert CO2 into value-added chemicals for a carbon-neutral society, especially when powered by renewable electricity. However, ECR still faces major challenges, including low current densities and limited stability. Flow-cell electrolyzers incorporating gas diffusion electrodes (GDEs) have emerged as a superior alternative to conventional immersed-type H-cells. Notably, only hydrophobic GDEs can be employed as cathodes for ECR, as the unique GDE–catalyst–electrolyte interface establishes a stable gas–liquid–solid three-phase boundary. This architecture significantly enhances mass transport and enables high-rate electrocatalysis. In this tutorial, we present a standardized design framework for flow-cell electrolyzers and outline strategies to optimize GDEs by expanding three-phase boundaries to achieve high-performance ECR. We also summarize key operational considerations and provide case studies for analyzing both liquid and gaseous products at ampere-level partial current densities. While previous tutorials have largely focused on membrane electrode assembly (MEA) electrolyzers, such systems are costly, complex, and sensitive to membrane hydration. To address these limitations, we introduce a newly designed half-reaction flow-cell electrolyzer that is simpler, transparent, and modular. This configuration enables rapid evaluation of cathode catalysts and direct visualization of flooding or salt deposition. Finally, we provide a comprehensive protocol covering system assembly, calibration, electrochemical evaluation, and product quantification. By integrating theoretical context with practical methodology, this tutorial aims to improve reproducibility, ensure data reliability, and advance efficient, scalable ECR technologies.