Enhancing Direct Electrochemical CO₂ Electrolysis by Introducing A-Site Deficiency for the Dual-Phase Pr(Ca)Fe(Ni)O_3−δ Cathode

High-temperature CO₂ electrolysis via solid oxide electrolysis cells (CO₂–SOECs) has drawn special attention due to the high energy convention efficiency, fast electrode kinetics, and great potential in carbon cycling. However, the development of cathode materials with high catalytic activity and chemical stability for pure CO₂ electrolysis is still a great challenge. In this work, A-site cation deficient dual-phase material, namely (Pr_0.4Ca_0.6)_xFe_0.8Ni_0.2O_3−δ (PCFN, x = 1, 0.95, and 0.9), has been designed as the fuel electrode for a pure CO₂–SOEC, which presents superior electrochemical performance. Among all these compositions, (Pr_0.4Ca_0.6)_0.95Fe_0.8Ni_0.2O_3−δ (PCFN95) exhibited the lowest polarization resistance of 0.458 Ω cm² at open-circuit voltage and 800 °C. The application of PCFN95 as the cathode in a single cell yields an impressive electrolysis current density of 1.76 A cm⁻² at 1.5 V and 800 °C, which is 76% higher than that of single cells with stoichiometric Pr_0.4Ca_0.6Fe_0.8Ni_0.2O_3−δ (PCFN100) cathode. The effects of A-site deficiency on materials' phase structure and physicochemical properties are also systematically investigated. Such an enhancement in electrochemical performance is attributed to the promotion of effective CO₂ adsorption, as well as the improved electrode kinetics resulting from the A-site deficiency.