Improving the lifetime of hybrid CoPc@MWCNT catalysts for selective electrochemical CO₂-to-CO conversion

Highlights

• Hybrid CoPc@MWCNT electrocatalyst selectively convert CO₂ to CO.

• Deterioration of catalyst performance occurs during long-term CO₂ electrolysis.

• The deterioration is partially related to demetalation of CoPc induced by Fe codeposition.

• Minimizing Fe contaminations significantly improves catalyst lifetime.

• For the Fe-free catalyst, FE_CO remains above 96% during 95 h of CO₂ electrolysis.

Abstract

Molecular hybrid catalysts, such as cobalt(II) phthalocyanine (CoPc) complexes anchored to multi-walled carbon nanotubes (MWCNTs), provide selective CO₂ conversion toward CO with high current densities, exceeding 0.1 A cm⁻² in microfluidic or zero-gap (membrane) electrolyzers. However, the practicality of CO₂ electroreduction is essentially determined by the catalyst stability against mechanical and (electro)chemical degradation. Here, we report a new mechanism for the observable degradation of the CoPc@MWCNT hybrid catalyst. Even at moderate CO₂ reduction potentials, the demetalation of CoPc complexes is induced by a reduction of iron (Fe) species, which can contaminate commercially available MWCNTs or solvents used for catalyst preparation. Minimization of Fe contamination leads to a substantial improvement in the CoPc@MWCNT catalyst lifetime, with the faradaic efficiency of CO formation decreasing from 98% to 96% (by only 2%) after 95 h of electrolysis. Thus, careful purification of hybrid catalyst materials is required to maintain initial levels of catalyst performance during long-term operation.