To study the synergy between the transition metals for enhancing the electrochemical and chemical activity, a series of SOECs were modified with a small amount of Co ions, namely 1.8, 3.6, and 5.4 wt% in the reduced state.

Full characterization involving STXM imaging allowed for better understanding of the synergy between the Ni and Co host metal and made it possible to find the causes of the increased activity. It revealed the complexity of the substructures formed within the electrode. The performance tests indicated the roles of both rWGS and direct electrolysis of CO₂ in the electroreduction process.

The modifications on SOECs consisted of the introduction of small amounts of Co into the Ni-YSZ cermet material of the cells via the wet impregnation method. Thanks to the STXM imaging coupled with XAS measurements it was observed that the Co ions formed three types of substructures, namely nanoparticles of Co_xO_y supported on the surface of the 8YSZ, Ni-Co mixed spinel-like compound on the interface between the Ni core and outer layer, and Co_xO_y nanoparticles embedded into the spinel scale (Fig. 1.). The XPS results indicated that Co induced the formation of a high amount of the available catalytic sites through the active Ni³⁺/Ni²⁺ and Co³⁺/Co²⁺ couples for reactions to happen. The performed modifications increased the CH₄ concentration in the outlet stream over 2.5 times and ensured better efficiency of the H₂O/CO₂ co-electrolysis (Fig. 2). The search for the possible causes of the enhancement through XAS and STXM measurements resulted in direct proof of the existence of a significant amount of the intermixed Ni-Co compound which induced changes in the shift of the EF band energy, generated the inverse spinel structure, and introduced a significant amount of active surface species. The STXM measurements clearly evidenced a Co-graduated structure of core-shell-like Ni grains. The addition of the secondary metal into the Ni-YSZ conventional cermet material revealed highly promising results to be further applied in the field of H₂O/CO₂ co-electrolysis with the simultaneous single-process of methanation for the buildup of advanced conversion systems.

Fig.1. STXM images of the as-prepared 3.6 wt % Co-impregnated sample with the corresponding elemental distribution maps of Ni and Co. The Ni and Co map overlay is also presented.

Fig,2, Concentration of CH₄ in the outlet stream at OCV (A) and 1.3 V (B). Equilibrium concentration marked as dashed line. (C) Current densities at 1.3 V vs. temperature. Dashed lines are visual guides only.

Full publication available below:

P. Blaszczak, M. Zajac, A. Ducka, K. Matlak, B. Wolanin, S. F. Wang, A. Mandziak, B. Bochentyn, and P. Jasinski, High-Temperature Co-Electrolysis of CO2/H2O and Direct Methanation over Co-Impregnated SOEC. Bimetallic Synergy between Co and Ni, Int J Hydrogen Energy 47, 35017 (2022). doi:10.1016/j.ijhydene.2022.08.057