The electrochemical conversion of CO2 into liquid fuels offers alternative ways to produce renewable fuels and store the surplus renewable energy. However, significant chemistry challenges still remain, particularly in relation to the kinetic inertness of CO2 and thermodynamic complexity of the multiple electron transfer processes involved. We describe a new type of flow-Through membrane reactor, based on a hierarchically ordered platinum nanochannel array with macropore channels in combination with mesoporous walls. The membrane reactor exhibits unique three-dimensional electrocatalytic interfaces with high activity and selectivity in CO2 conversion producing methanol and ethanol as the dominant liquid products. The Faradaic efficiency and yield for alcohol production are up to 23.9% and 2.1 × 10-8 mol s-1 cm-2 at 51 mA/cm-2, respectively. Experimental and density functional theory studies evidence that substantial (110) facets and a high density of atomic surface steps contribute significantly to the intrinsic activity and selectivity for conversion of CO2 to alcohol.