Spatial effects define CO2 electrolysis systems

CO2 electrolyzers show promise as a cleaner alternative to produce value-added chemicals. In the last decade, research has shifted from classifying CO2 reduction activity and selectivity as a catalytic property (zero-dimensional [0D]) to one that includes the complex interactions of gas, liquid, and solid species between the cathode and anode (1D). To scale CO2 electrolyzers, however, 2D and 3D spatial variations in product selectivity, activity, and stability arise due to the design of reactor components, as well as concentration variations of the reactants, intermediates, and products. Conventional “black-box” measurement protocols are then insufficient to characterize CO2 electrolyzers. Here, we discuss the critical multi-dimensional phenomena occurring inside these electrochemical systems, which impact the observed performance. Recent literature is used to demonstrate how a spatial perspective is essential for proper data interpretation, designing effective catalysts, and prolonging CO2 electrolyzer lifetimes. Researchers should then define CO2 electrolysis systems in multiple dimensions (2D and 3D).