Improving the lifetime of hybrid CoPc@MWCNT catalysts for selective electrochemical CO2-to-CO conversion
Changzhe Sun, Yuhui Hou, Nicola Lüdi, Huifang Hu, María de Jesús Gálvez‐Vázquez, Mike Liechti, Ying Kong, Menglong Liu, Rolf Erni, Alexander V. Rudnev, Peter Broekmann
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 [email protected] 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 [email protected] 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.