A long-standing goal of chemistry is to synthesize organic compounds from CO2 and H2O to mimic natural photosynthetic processes. Achieving this goal requires catalysts and methods that activate CO2 and split water simultaneously. Here we report such catalysts and methods for the synthesis of paraformaldehyde from CO2 and H2O at atmospheric pressure. The activation was realized by polarizing metal/metal oxide interfaces with a DC voltage or current. The selectivity to paraformaldehyde was as high as 100% and CO2 conversion up to 8%. Both Pt/CSZ and Pt/MnO2 catalysts with ionic conductivity and mixed conductivity respectively produced paraformaldehyde. The former works at high temperatures of 600-900 degrees C; the latter works at low temperatures of 300-450 degrees C. This gas-phase electrocatalysis technique provides new insight into the utilization of CO2 as a carbon source in organic chemical syntheses and in the clean activation of CO2. (c) 2010 Elsevier B.V. All rights reserved.