(Digital Presentation) Finding the Optimum Loading of Fe & Au in NiO/GDC, for the Reversible Operation of Solid Oxide Cells
Authors: Zaravelis Fotios , Niakolas Dimitris K. , Neophytides Stylianos G. 
Published: September 2023

Reversible solid oxide cells (rSOCs) are ideal candidates for renewable energy storage and usage, due to their ability to work under electrolysis mode for H2 production or fuel cell mode for power generation, both by the same unit. Operation of SOCs at high-temperatures enables high energy efficiency, increases reaction rates, and allows the use of low-cost catalysts compared to low temperature technologies. The state-of-the-art (SoA) fuel electrodes: Ni/YSZ and Ni/GDC, despite their advantages, are prone to various degradation phenomena, such as Ni coarsening, agglomeration, and depletion/migration. One way to mitigate these issues is by dispersing small amounts of transition metal additives, either non-noble or noble elements, into the Ni-based electrode [1, 2, 3].

Recent studies [1] on how Fe interacts with Ni in Ni/GDC showed that the enhancing effect of Fe on the electrochemical performance under electrolysis conditions is constrained by its wt.% concentration, whereas even if the electrode exhibited high activity, it was prone to fast degradation. In our latest work, we presented a first attempt on co-depositing Fe and Au, with the primary objective being the stabilization of the enhancing effect of Fe on Ni/GDC. Thus, an electrode consisted of the, by that time, best performing loadings was synthesized, namely 0.5 wt.% Fe and 3 wt.% Au, showcasing the enhancing effect of this modification on both the activity and stability, under rSOC operation. The superiority of this electrode is primarily ascribed to the induced changes by the Fe-Au-modification on the intrinsic electrochemical characteristics, as indicated by the ohmic and polarization resistance values. These are far lower to those of Ni/GDC and of the optimum Au-Mo-modified electrode [3], particularly under SOE operation. Another remark is the rSOC stability of both electrochemical characteristics, but especially of the Rpol
.

The presented study focuses on how each of the Au and Fe modifiers affects the physicochemical and electrochemical characteristics of the electrode. In this respect, several electrocatalysts were synthesized, consisted of different Au and Fe loadings, and then evaluated under r-SOC operation. By reducing the Au concentration to 1 wt.%, the performance of the electrode increased, which is attributed mainly to the lower Rohm
values, and less to these of Rpol
that remain practically constant. On the other hand, by increasing the Fe loading to 2 wt.% and by keeping the Au loading to 3 wt.%, the electrode had the same initial performance, but after three rSOC cycles the performance slightly dropped, due to the increase of both Rohm
and Rpol
values. In parallel to the electrochemical measurements, physicochemical characterization is performed for further elucidation of the electrodes/powders properties.

References

[1] Neofytidis, C., Ioannidou, E., Kollia, M., Neophytides, S. G., & Niakolas, D. K. (2020). The promoting effect of Fe on Ni/GDC for the Solid Oxide H2O electrolysis. International Journal of Energy Research, 44(13), 10982–10995.

[2] Neofytidis, C., Ioannidou, E., Sygellou, L., Kollia, M., and Niakolas, D.K. Affecting the H2O electrolysis process in SOECs through modification of NiO/GDC; experimental case of Au-Mo-Ni synergy. J. Catal., vol. 373, pp. 260–275, 2019.

[3] Zaravelis, F., Souvalioti, A., Neophytides, S., Niakolas, D.K. (2023). Transition metals in Ni/GDC for the Reversible Solid Oxide Cell operation: Optimization of the Mo-Au-Ni synergy and further enhancement via substitution of Mo with Fe. (Under submission).