Electrochemical reduction of carbon dioxide (CO2) is an appealing approach toward tackling climate change associated with atmospheric CO2 emissions. This approach uses CO2 as the carbon feedstock to produce value‐added chemicals, resulting in a carbon‐neutral (or even carbon‐negative) process for chemical production. Many efforts have been devoted to the development of CO2 electrolysis devices that can be operated at industrially relevant rates; however, limited progress has been made, especially for valuable C2+ products. Herein, a nanoporous copper CO2 reduction catalyst is synthesized and integrated into a microfluidic CO2 flow cell electrolyzer. The CO2 electrolyzer exhibits a current density of 653 mA cm−2 with a C2+ product selectivity of ≈62% at an applied potential of −0.67 V (vs reversible hydrogen electrode). The highly porous electrode structure facilitates rapid gas transport across the electrode–electrolyte interface at high current densities. Further investigations on electrolyte effects reveal that the surface pH value is substantially different from the pH of bulk electrolyte, especially for nonbuffering near‐neutral electrolytes when operating at high currents. A nanoporous copper catalyst for CO2 reduction is synthesized and integrated into a microfluidic CO2 flow cell electrolyzer with well‐engineered electrode–electrolyte interface. The CO2 electrolyzer exhibits a current density over 650 mA cm−2 with a C2+ product selectivity of ≈62% at a mild overpotential, which represents one of the highest performances that have been achieved to date.