Effect of loading and pyrolysis of carbon-supported cobalt phthalocyanine on the electrocatalytic reduction of CO2

Abstract

Understanding the structure-activity relationship of materials that are active for the CO2 electrochemical reduction reaction (CO2ERR) is crucial for developing stable, high-performance catalysts. In this research, it is first shown that ball-milling is a highly efficient way to disperse cobalt phthalocyanine (CoPC) onto carbon black without influencing the CO2 electroreduction performance of the resulting materials. Then, the link between the loadings of the CoPC precursor on the carbon support and the CO2ERR activity of the pyrolyzed materials is demonstrated. With CO current efficiencies higher than 45% and CO current densities as high as -20 mA cm−2 at -0.77 V vs. RHE, the materials with CoPC loadings of 7.9 wt% and higher were still surprisingly active after pyrolysis at 800 and 900 °C. On the other hand, the CO2ERR activity of the materials containing less than 6.1 wt% CoPC was drastically reduced after pyrolysis at these temperatures, with CO current efficiencies lower than 10 %. X-ray powder diffraction revealed that only the materials containing crystalline CoPC before pyrolysis showed good CO2ERR activity after pyrolysis at 800 and 900 °C. Furthermore, X-ray absorption spectroscopy showed that the loading of the CoPC precursor influenced the structure of the active sites in the pyrolyzed CoPC/C materials. Overall, this study highlights the importance of the dispersion of CoPC when forming a material that is catalytically active for CO2ERR after pyrolysis.