Impact of Cu Alloying in a Ni-Based Cathode on Carbon Deposition Tolerance during CO ₂ /H ₂ O Electrolysis in SOECs via DFT Calculations

The effects of Ni–Cu alloying and electrolytes on carbon deposition were investigated through experiments and density functional theory (DFT) calculations. The electrochemical performances of Ni/YSZ and NiCu/YSZ were nearly identical in CO 2 /H 2 O electrolysis, indicating that Cu alloying only slightly influenced CO 2 reduction activity. However, scanning electron microscopy/EDS showed that carbon deposition observed on Ni/YSZ at a lower electrolysis current density (0.07 A/cm 2 (∼1.3 V)) was considerably suppressed on NiCu/YSZ due to Ni–Cu alloying. DFT calculations revealed that Cu addition decreased CO adsorption energy and increased the activation barrier for CO dissociation on the Ni surface by ∼0.6 eV, thereby suppressing carbon formation. However, carbon deposition was observed even on NiCu/YSZ at a higher electrolysis current density (0.14 A/cm 2 (∼1.5 V)), indicating that Ni–Cu alloying alone was insufficient to prevent carbon formation under severe conditions. Further DFT analysis showed that CO dissociation via oxygen-vacancy exchange at the triple-phase boundary was insensitive to Cu alloying and became dominant under high applied voltages. In contrast, no carbon deposition was observed on NiCu/GDC (0.14 A/cm 2 (∼1.3 V) and 0.28 A/cm 2 (∼1.5 V)), demonstrating that the electrolyte played a key role in suppressing oxygen vacancy–mediated carbon formation.