Theis Skafte2 Max García-Melchor3 Michal Bajdich1 William C. Chueh1 Christopher Graves2

2, Technical University of Denmark, Roskilde, , Denmark
3, The University of Dublin, Dublin, , Ireland
1, Stanford University, Menlo Park, California, United States

Nickel-based electrodes and catalysts are often utilized in high-temperature electrochemical CO2 reduction due to their high performance and low cost. However, nickel is also an excellent catalyst for destructive carbon deposition, which can be mitigated by the use of ceria. In this work, we elucidate the inhibition mechanism during electrochemical CO2 reduction on dense thin-film model-electrodes consisting of samarium-doped ceria, nickel, and yttria-stabilized zirconia. The results obtained via operando x-ray photoelectron spectroscopy show hat ceria-based electrodes require higher onset overpotentials for carbon deposition and have a high surface coverage of carbonate species. Our density functional theory calculations reveal the crucial role of the surface carbonates as energetic traps that inhibit carbon formation and show that this is most effective with non-stoichiometric CeO2-δ(100) surfaces. This destabilization of carbon leads to a thin amorphous carbon layer instead of the destructive carbon nanotubes that grow on nickel without ceria present.