Engineering the heterogeneous catalyst of protonic ceramic electrochemical cells for CO₂/H₂O co-electrolysis

Protonic ceramic electrochemical cells (PCECs) are highly promising electrochemical devices for CO₂/H₂O co-electrolysis reactions. However, conventional Ni/BaZr_0.4Ce_0.4Y_0.1Yb_0.1O₃ (BZCYYb) heterogeneous catalysts have exhibited limited catalytic activity for CO₂ methanation, hindering their further utilization and application. To address this challenge, we have developed a Ca-modified Ni/BZCYYb heterogeneous catalyst. We firstly evaluated the CO₂ conversion of the Ca-Ni/BZCYYb catalyst in a packed bed reactor, and found that it exhibited higher CO₂ conversion at lower operating temperature compared to the Ni/BZCYYb catalyst. Furthermore, we have demonstrated significantly improved CO₂-H₂O co-electrolysis performance in PCECs by modifying the fuel electrode with a Ca-Ni/BZCYYb heterogeneous catalyst. This modification results in a substantially improved CO₂ conversion of ∼40% and CH₄ production of 1.22 ml min⁻¹ at 500 °C compared to the reference PCECs, validating the practical applicability of our approach in electrochemical devices. Surface characterization and density functional theory calculations reveal that CaO donates electrons to the BZCYYb catalyst support, facilitating the formation of oxygen vacancies, which provide preferential sites for CO₂ adsorption, thus enhancing CO₂ activation. This study demonstrates the potential of engineering the surface basicity for PCECs operating at low temperatures.