Abstract
Understanding the nature of the reactive sites of CO2 reduction catalysts is crucial to developing efficient and selective materials to help mitigate the greenhouse effect. In this research, materials based on cobalt phthalocyanine supported by carbon black and pyrolyzed at various temperatures under argon are fabricated and tested for CO2 electroreduction. The results show that the high reactivity of the catalysts for the electro-reduction of CO2 to CO is maintained for materials prepared at temperatures up to 700 degrees C, with CO Faradaic efficiencies of >85% and CO current densities consistently at >40 mA cm-2 at -0.86 V vs RHE. The materials annealed up to 900 degrees C are also remarkably active, with CO Faradaic efficiencies of >40% and CO current densities of >12 mA cm-2. The combination of X-ray diffraction, infrared and Raman spectroscopies, and X-ray absorption analysis show that the annealed materials exhibit chemical structures drastically different from those of the original CoPC and unsupported pyrolyzed catalyst while highlighting the role of the carbon black support in the formation of active species. These results give crucial insight into the reactive structure of CoPC and open the way for the development of pyrolyzed Co-N4 macrocycles as a new class of materials efficient for the electroreduction of CO2.