Mechanism of CO<sub>2</sub> Electroreduction to Multicarbon Products over Iron Phthalocyanine Single-Atom Catalysts
Reza Khakpour, Kaveh Farshadfar, Si‐Thanh Dong, Benedikt Lassalle‐Kaiser, Kari Laasonen, Michael Busch
Abstract
High Resolution Image Download MS PowerPoint Slide Carbon dioxide reduction reaction (CO 2 RR) is a promising method for converting CO 2 into value-added products. CO 2 RR over single-atom catalysts (SACs) is widely known to result in chemical compounds such as carbon monoxide and formic acid that contain only one carbon atom (C1). Indeed, at least two active sites are commonly believed to be required for C–C coupling to synthesize compounds, such as ethanol and propylene (C 2+ ), from CO 2 . However, experimental evidence suggests that iron phthalocyanine (PcFe), which possesses only a single metal center, can produce a trace amount of C 2+ products. To the best of our knowledge, the mechanism by which C 2+ products are formed over a SAC such as PcFe is still unknown. Using density functional theory (DFT), we analyzed the mechanism of the CO 2 RR to C1 and C 2+ products over PcFe. Due to the high concentration of bicarbonate at pH 7, CO 2 RR competes with HCO 3 – reduction. Our computations indicate that bicarbonate reduction is significantly more favorable. However, the rate of this reaction is influenced by the H 3 O + concentration. For the formation of C 2+ products, our computations reveal that C–C coupling proceeds through the reaction between in situ-formed CO and PcFe(“0”)–CH 2 or PcFe(“-I”)–CH 2 intermediates. This reaction step is highly exergonic and requires only low activation energies of 0.44 and 0.24 eV for PcFe(“0”)–CH 2 and PcFe(“-I”)–CH 2 . The DFT results, in line with experimental evidence, suggest that C 2+ compounds are produced over PcFe at low potentials whereas CH 4 is still the main post-CO product.