Praseodymium Doped Ceria as Nickel-Free Fuel Electrode Material for Solid Oxide Electrolysis Cells

Solid Oxide Electrolysis Cells (SOECs) play a key role in power-to-gas applications as a relevant electrochemical conversion device for addressing the global energy crisis. It uses electrical energy to transform naturally abundant chemicals like H 2 O or CO 2 into high energy-density or industrially relevant gases such as H 2 , CO, and CH 4 [1]. The current SoA fuel electrode materials: Ni-YSZ and Ni-GDC, enable efficient electrochemical reactions at high temperatures (600°C–900°C). However, when operating at high current density, they exhibit some serious issues such as nickel migration and agglomeration, which ultimately reduce the SOEC durability and lifetime [2], [3]. As a result, researchers are investigating Ni-free mixed ionic-electronic conductor (MIEC) based fuel electrode materials, for example, perovskites or single-phase doped ceria [4], [5]. In this context, recent studies on single-phase gadolinium-doped ceria (GDC) fuel electrodes have demonstrated improved durability and electrochemical performance over Ni-YSZ; however, it is still a challenge to surpass the electrochemical performance and durability of single-phase doped ceria over Ni-GDC [6], [7]. To address this issue, this research explores the potential of incorporating single-phase praseodymium-doped ceria (PDC) as an alternative fuel electrode material. Specifically, three concentrations of doped ceria materials: 5% lanthanum and 5% praseodymium doped ceria (LPDC: La 0.05 Pr 0.05 Ce 0.9 O 2-δ ), 10% praseodymium doped ceria (PDC10: Pr 0.1 Ce 0.9 O 2-δ ), and 30% praseodymium doped ceria (PDC30: Pr 0.3 Ce 0.7 O 2-δ ) were used as fuel electrode to fabricate electrolyte-supported single cells. The cell denomination for the LPDC, PDC10, and PDC30 based single cells are LPDC/GDC/8YSZ/GDC/LSCF, PDC10/GDC/8YSZ/GDC/LSCF, and PDC30/GDC/8YSZ/GDC/LSCF, respectively. At 900°C, under steam electrolysis conditions: 50% H 2 + 50% H 2 O, PDC10 outperforms both LPDC (-1.37 A/cm²) and PDC30 (-1.1 A/cm²), achieving a current density of -1.5 A/cm² at 1.5 V (see attached figure) [6], [8], [9]. In addition, the electrochemical performance (I-V characteristics and EIS) was investigated. The structural and chemical properties of these three materials were also analyzed using XRD, TGA, Raman spectroscopy, and XPS to evaluate their physicochemical behaviour at a fundamental level. In conclusion, these results suggest that single-phase praseodymium doped ceria-based materials could be a promising alternative in the search for efficient and durable Ni-free fuel electrode materials for SOECs. Literature : [1] A. Hauch et al., “Recent advances in solid oxide cell technology for electrolysis,” Science (1979), vol. 370, no. 6513, Oct. 2020, doi: 10.1126/science.aba6118. [2] C. Graves, S. D. Ebbesen, S. H. Jensen, S. B. Simonsen, and M. B. Mogensen, “Eliminating degradation in solid oxide electrochemical cells by reversible operation,” Nat Mater, vol. 14, no. 2, pp. 239–244, 2015, doi: 10.1038/nmat4165. [3] D Simwonis, F. Tietz, D. Stover, and S. Stover, “Nickel coarsening in annealed Ni / 8YSZ anode substrates for solid oxide fuel cells In memoriam to Professor H. Tagawa,” 2000. [4] S. E. Wolf et al., “Solid oxide electrolysis cells - current material development and industrial application,” Jul. 10, 2023, Royal Society of Chemistry. doi: 10.1039/d3ta02161k. [5] E. M. Sala et al., “Unravelling the role of dopants in the electrocatalytic activity of ceria towards CO 2 reduction in solid oxide electrolysis cells,” Physical Chemistry Chemical Physics, vol. 25, no.4, pp. 3457–3471, Jan. 2023, doi: 10.1039/d2cp05157e. [6] J. Uecker, I. D. Unachukwu, V. Vibhu, I. C. Vinke, L. G. J. de Haart, and R. A. Eichel, “Gadolinium Doped Ceria as Nickel–Free Fuel Electrode in High Temperature CO 2 -Electrolysis,” ChemElectroChem, 2024, doi: 10.1002/celc.202300617. [7] A. Nenning, M. Holzmann, J. Fleig, and A. K. Opitz, “Excellent kinetics of single-phase Gd-doped ceria fuel electrodes in solid oxide cells,” Mater Adv, vol. 2, no. 16, pp. 5422–5431, Aug. 2021, doi: 10.1039/d1ma00202c. [8] I. D. Unachukwu, V. Vibhu, I. C. Vinke, R. A. Eichel, and L. G. J. (Bert) de Haart, “Electrochemical and degradation behaviour of single cells comprising Ni-GDC fuel electrode under high temperature steam- and co-electrolysis conditions,” J Power Sources, vol. 556, Feb. 2023, doi: 10.1016/j.jpowsour.2022.232436. [9] I. D. Unachukwu, V. Vibhu, J. Uecker, I. C. Vinke, R.-A. Eichel, and L. G. J. (Bert) de Haart, “ Comparison of the Electrochemical and Degradation Behaviour of Ni-YSZ and Ni-GDC Electrodes Under Steam, Co- and CO 2 Electrolysis ,” ECS Trans, vol. 111, no. 6, pp. 1445–1452, May 2023, doi: 10.1149/11106.1445ecst. Figure 1