In-situ growing nickel phthalocyanine supramolecular structure on carbon nanotubes for efficient electrochemical CO2 conversion

Heterogeneous catalysts made up of molecule-based catalysts on conductive substrates enable the large current density, high selectivity, and easy operation for carbon dioxide reduction reaction towards the practical use. Herein, we report a hydrogen-bonded supramolecular structure (1) assembled from asymmetric A3B-type nickel phthalocyanine NiPc(OH)6(DCNFO), which is afforded via solvothermal reaction of 2,3,9,10,16,17,23,24-octahy-droxyl-phthalocyaninato nickel with tetrafluoroterephthalene. Single crystal X-ray diffraction analysis reveals the one-dimensional supramolecular ribbons of 1 formed from individual modules via hydrogen-bond between the hydroxyl groups, showing good solution resistance due mainly to the additional strong 7C-7C interactions. Nevertheless, in-situ growing 1 on carbon nanotubes generates a phthalocyanine-based composite for gas diffusion electrode, displaying the highly selective conversion of CO2 to CO with Faradaic efficiency > 98% at a wide voltage range from -0.5 to -1.2 V versus reversible hydrogen electrode, a high current density of 353 mA cm-2 at -1.2 V, and stable cycling at 150 mA cm-2 for 40 h in 0.5 M KHCO3 electrolyte. Employment of 1.0 M KOH results in a further improved current density of 620 mA cm-2 at -1.2 V and higher stable cycling current density of 230 mA cm-2 for 40 h.