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

• Published in: Journal of catalysis 2022-03, Vol.407, p.198-205
• Main Authors: Sun, Changzhe, Hou, Yuhui, Lüdi, Nicola, Hu, Huifang, de Jesús Gálvez-Vázquez, María, Liechti, Mike, Kong, Ying, Liu, Menglong, Erni, Rolf, Rudnev, Alexander V., Broekmann, Peter
• Format: Article
• Language: English
• Subjects: Carbon monoxide; Carbon nanotubes; Catalyst degradation; CO2 electroreduction; Cobalt phthalocyanine; Molecular catalyst
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2022.02.001

[Display omitted] •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, FECO remains above 96% during 95 h of CO2 electrolysis. 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.