Non-peripheral octamethyl-substituted cobalt phthalocyanine nanorods supported on N-doped reduced graphene oxide achieve efficient electrocatalytic CO2 reduction to CO

Abstract

Developing electrocatalysts that exhibit highly-efficient CO2reduction is crucial for a healthier environment. This report demonstrates that the eight methyl groups on cobalt phthalocyanine significantly improved its catalytic CO2 reduction performance. Theoretical computations confirmed that the non-peripheral octamethyl-substituted cobalt(II) phthalocyanine (N-CoMe2Pc) catalyst showed enhanced CO2 adsorption and activation on the Co surface at low overpotentials relative to pristine cobalt(II) phthalocyanine (CoPc). The N-CoMe2Pc nanorods and nitrogen-doped reduced graphene oxide (NRGO) nanocomposites were successfully prepared by a facile, non-covalent immobilization strategy and their electrocatalytic CO2 reduction activity was explored in both H-type and flow cell configurations. It was thus verified that immobilizing N-CoMe2Pc nanorods onto NRGO surfaces can lead to enhanced electroactivity and selectivity in terms of reducing CO2 to CO. Among the various tested nanocomposites, N-CoMe2Pc/NRGO with a catalyst: NRGO ratio of 6:10 showed superior CO faradaic efficiency/selectivity (90.0 %) and a total current density reaching 9.7 mA cm−2 at –0.8 V vs. RHE in an H-type cell containing a neutral electrolyte. A CO faradaic efficiency of 90.4% and a current density of 14.8 mA cm−2 were achieved at the same overpotential using a flow cell. The selectivity of this system was further improved to 94.1%, with an accompanying CO current density of 56.4 mA cm−2 and an impressive turnover frequency of 6.2 s−1 at lower potential (–0.6 V vs. RHE) in alkaline solution. This work provides new insights relevant for developing low-cost, effective, phthalocyanine-based catalysts for electrochemical CO2 reduction.