Enhancing effect of cobalt phthalocyanine dispersion on electrocatalytic reduction of CO 2 towards methanol.

This paper focuses on enhancing the performance of electrocatalytic CO ₂ reduction reaction (CO ₂ RR) by improving the dispersion of cobalt phthalocyanine (CoPc), especially for the methanol formation with multi-walled carbon nanotubes (CNTs) as a support. The promising CNTs-supported CoPc hybrid was prepared based on ball milling technique, and the surface morphology was characterized by means of those methods such as scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FT-IR) and X-ray photoelectron spectra (XPS). Then, the synergistic effect of CNTs and ball milling on CO ₂ RR performance was analyzed by those methods of cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), gas chromatography (GC), and proton nuclear magnetic resonance spectroscopy ( ¹ HNMR). Subsequently, the reduction mechanism of CO ₂ on ball-milled CoPc/CNTs was revealed based on the DFT calculations. The results showed that the electrocatalyst CoPc/CNTs hybrid prepared with sonication exhibited a conversion efficiency of CO ₂ above 60% at -1.0 V vs. RHE, accompanied by the Faradaic efficiencies of nearly 50% for CO and 10% for methanol, respectively. The addition of CNTs as the support improved the utilization efficiency of CoPc and reduced the transfer resistance of species and electrons. Then the ball-milling method further improved the dispersion of CoPc on CNTs, which resulted in the fact that the methanol efficiency was raised by 6% and partial current density was increased by nearly 433%. The better dispersion of CoPc on CNTs adjusted the reduction pathway of CO ₂ and resulted in the enhancement of methanol selectivity and catalytic activity of CO ₂ . The probable pathway for methanol production was proposed as CO ₂  → *CO ₂ ^-  → *COOH → *CO → *CHO → *CH ₂ O → *OCH ₃  → CH ₃ OH. This suggests the significance of the ball-milling method during the preparation of better supported catalysts for CO ₂ RR towards those high-valued products.
(© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)