The primary difference between these architectures is a roughly 3-order of magnitude reduction in the CO2 diffusion pathway to the surface of the catalyst: from ~50 μm in an Hcell to ~50 nm using a gas-diffusion layer (Fig. ), which allows for the increased maximum current densities reported in literature. Using a simple 1D reaction-diffusion model developed previously, we can also approximate the similarities and differences in the local catalytic environments as a function of reaction rate for both cases.