The abovementioned results follow from a model that tries to capture the device's essential features while otherwise remaining as simple as possible, schematically shown in Figure . To bridge the length scales ranging from nm inside the pores to mm for the overall device, we let a single nanochannel (middle channel in Figure ) of radius 𝑅 c = 2.5 nm and length 𝐻 = 50 nm represent the complex porous structure of an electrode. Diffusion barriers at either end of the nanochannels approximate the mm device features and slow down diffusion via a simple linearised diffusive flux over a distance of 0.5 mm. The effective thickness of the computational model is thicker than the physical device, but the actual lengths of the pathways can also vary considerably in the porous electrodes. Therefore we chose the thickness of 0.5 mm for simplicity. Uncharged pathways (left and right channels in Figure ) are also present alongside the charged nanochannels to model the larger mesopores in each electrode, whose charge screened surfaces do not affect the majority of the internal volume due to their larger radii, rendering them effectively uncharged. Lastly a gas chamber is in contact with the electrolyte at one side of the system, which can freely exchange CO2 with the electrolyte. The entire system is azimuthally symmetric around its central axis.