The number of CO2 electroreduction experiments reported at elevated current densities is rapidly increasing, owed in part to the maturity of the field as well as the observed performance benefits. Recent work has reviewed various electrochemical architectures capable of delivering enough CO2 to the catalyst to reach current densities >200 mA/cm 2 , summarizing in detail the impacts of different components and configurations on system performance. While we refer the reader to these publications for specific technical advances in the field, we will briefly summarize several commonly-used architectures (Fig. ) and aspects of their operation to illustrate how the reaction environment around the catalyst layer is influenced by elevated current densities. Cell view for a catalyst deposited on a gas-diffusion layer with a flowing catholyte channel, (c) Cell view for a catalyst deposited on a gas-diffusion layer with a non-flowing catholyte, (d) species transport to and from a catalyst layer in which CO2 is supplied via diffusion from the bulk electrolyte on the microscale (~50 µm). (e) a CO2 reduction catalyst layer deposited onto a hydrophobic substrate with CO2 diffusion from a nearby gas-liquid interface (~50 nm). Liquid species diffuse to the ionexchange membrane through either a bulk flowing electrolyte or a solid-supported electrolyte layer.