Ni-doped CeO2 nanoparticles to promote and restore the performance of Ni/YSZ cathodes for CO2 electroreduction

Despite the considerable efforts to develop innovative electrode materials, nickel/yttria-stabilized zirconia (Ni/YSZ) electrodes are still employed in nearly all commercial and industrial solid oxide cell units. This is because Ni/YSZ cermets have good electrocatalytic activity in both electrolysis and fuel cell modes, while they are cost-effective as compared to alternative electrodes under development at the lab scale. Infiltration of nanoparticles has immersed as a promising concept to enhance the performance and robustness of conventional Ni/YSZ. Herein, we apply a relatively simple procedure to infiltrate Ni/YSZ electrodes with hexane solution containing prefabricated Ni-doped CeO2 nanoparticles. Cells with modified Ni/YSZ electrodes show a great improvement in the electrocatalytic activity and stability towards direct CO2 reduction as compared to unmodified cathodes. Besides, a single infiltration step is sufficient to achieve the optimum cell performance, streamlining the preparation process. More importantly, we show that this strategy can be equally efficient to fully reactivate previously degraded Ni/YSZ electrodes and restore their electrochemical performance at levels even higher than the initial ones. In addition, due to the high viscosity of the hexane solution, Ni-doped CeO2 nanoparticles access the entire electrode volume all the way close to the YSZ interface, while it penetrates the micro cracks between Ni and YSZ particles. In this way the electrocatalytic reaction zone is recovered, and the degraded Ni/YSZ electrode is reactivated. Physicochemical, microstructural and electrochemical characterization of the cells evinces several effects that contribute to the performance improvement of Ni/YSZ after infiltration, such as the enhanced surface reducibility of Ni and the amelioration of charge transfer processes within the electrode. The simplicity of the proposed infiltration method and the significant promotion in CO2 electroreduction activity, advocate it as a cost-efficient strategy to improve or regenerate conventional Ni/YSZ electrodes without significantly altering the already well-established fabrication process.