Simple Preparation and Characterization of Hybrid Cobalt Phthalocyanine on Multiwalled Carbon Nanotube Electrodes

We report a simplified preparation of hybrid electrode materials with cobalt phthalocyanine (CoPc) on multiwalled carbon nanotubes using no binders or polymers and showing a high FECO = 91% and a moderate current density of 5.7 mA/cm2 for reducing CO2 to CO in near neutral pH aqueous electrolyte. We further characterize the hybrid materials by studying the effects of catalyst loading on solvent and the percentage of electroactive catalyst present. We observed that electrodes made with pure isopropyl alcohol as the ink preparation solvent had the best catalytic performance, but the percentage of electroactive catalyst did not change significantly with the catalyst loading. In contrast, electrodes made with dimethylformamide/isopropanol (1:1 v/v) showed an inverse relationship between catalyst loading and the electroactive percentage. Using characterization methods including scanning electron microscopy (SEM), chronoamperometry, and cyclic voltammetry, we show that ink preparation solvents have a dramatic effect on the surface morphology but a small effect on the catalytic microenvironment and performance of the electrode excluding samples prepared with isopropanol and phenol in IPA. Surface-immobilized crystallites of CoPc were observed through SEM and X-ray absorption near edge spectroscopy (XANES). Additionally, the ex situ XANES measurements suggest that the CoPc undergoes solvent-ligation further emphasizing the importance of solvent choice.