Crystalline Copper(II) Phthalocyanine Catalysts for Electrochemical Reduction of Carbon Dioxide in Aqueous Media

We achieved highly selective electrochemical reduction of CO2 to C2H4 (faradaic efficiency of 25%) by crystalline copper phthalocyanine (CuPc) supported on carbon black. Remarkably, noncrystalline CuPc generated by treatment of crystalline CuPc with sulfuric acid did not give C2H4 selectively, suggesting that catalyst crystallinity is crucial for the selective conversion of CO2 to C2H4. The stability of crystalline CuPc under electrochemical reduction conditions was also evaluated, showing that crystalline CuPc can selectively convert CO to C2H4 in the initial stage (<10 000 s), as long as the crystallinity of the catalyst is maintained.