Nanoparticles Infiltration into SOFC Cathode Backbones

Abstract

The last decade reveals the high potential of Solid oxide cells (SOC) as hydrogen battery storage operating to the demand either under fuel cell (concept gas-to-power) or electrolysis (concept power-to-gas) profiles. Such types of ceramic-based cells usually operate beyond 750°C in order to keep reasonable electrical performances and reliability of the whole electrochemical device. But, the high interest is to reduce the operating temperature in order to limit ageing parameters (Cr contamination, metal corrosion…) and improve energy efficiency while promoting cheaper materials and system processing. Actually, O2--conducting SOC suffers to an insufficient activity of the oxygen electrode and electrical performances at lower operation temperature. In such context, Protonic Ceramic Cell technology can overcome such technical hurdle below 700°C while taking benefit to produce water at the air electrode side, avoiding the dilution of the fuel. Proton Conducting Ceramic Cell technology is now widely investigated for a variety of applications, in particular fuel cell, steam electrolysis and hydrogen separation but such technology has to face to the lack of Technology Readiness Level for a viable way of market. From those bottlenecks raised two research strategies developed at EIFER: the improvement of anionic oxygen electrodes and the up-scaling and maturation of protonic ceramic cells. The infiltration of nanoparticles into a specific backbone could theoretically improve the electrochemical performance of the air electrode. It consists of the elaboration of a precursor’s solution which is then impregnated into the porosity of the electrode. The loading amount of the promoters have been optimized to decrease the polarization area specific resistance (ASRpol) and improve performance of intermediate temperature SOCs. Three different backbone materials were coated onto Yttria-stabilized zirconia pellets: La0.8Sr0.2MnO3 (LSM), Sm0.2Ce0.8O2-δ (SDC) and Nd1.95NiO4+δ (NdN). Several compositions were studied as promoter infiltrated inside the backbones: Sm0.5Sr0.5CoO3-δ (SSC), Sm0.2Ce0.8O2-δ (SDC), CeO2, Nd1.95NiO4+δ (NdN), Pr1.97NiO4+δ (PrN), and La0.8Sr0.2MnO3 (LSM). The infiltration loading and protocol were optimized to lower as much as possible the polarization resistances. For a temperature of 700°C, the lowest ASRpol was measured on a PrN promoter impregnated inside a NdN backbone (ASR=0.26 Ω.cm2), within the literature ASRs range[i],[ii] (see Figure 1).The elaboration of protonic ceramic cell has been deeply investigated in EIFER to improve the manufacturing process, increase the performance and the size of the cell and then to reach a higher TRL. Our group validated promising results on the elaboration and electrochemical characterization of middle-scaled protonic cells (until 20 cm²)[iii][iv][v], achieving interesting performances in fuel cell and electrolysis mode (P=0.25 W.cm-2 at E=0.8V and i=-0.35 A.cm-2 at E=1.2V respectively, at 700°C) and performed long-term test (> 3000 hours) under various profiles such as fuel cell (micro-cogeneration cycles), electrolysis (evaluation of operating conditions) and reversibility (fuel cell/electrolysis).The final target of this work is to merge both research strategies to improve performances of Protonic Ceramic Fuel Cells. The results will be discussed. [i] Shen, J., et al., Improved performance of a symmetrical solid oxide fuel cell by swapping the roles of doped ceria and La0.6Sr1.4MnO4+δ in the electrode, Journal of Power Sources, 2017, 342: p. 644-651. [ii] Shao, L., et al., Nanostructured CuCo2O4 cathode for intermediate temperature solid oxide fuel cells via an impregnation technique, Journal of Power Sources, 2017, 343: p. 268-274. [iii] Dailly, J., BCY-based proton conducting ceramic cell: 1000 h of long term testing in fuel cell application, Journal of Power Sources, 2013, 240: 323-327. [iv] Dailly, J., Evaluation of proton conducting BCY10-based anode supported cells by co-pressing method: Up-scaling, performances and durability, Journal of Power Sources, 2014, 255: 302-307. [v] Marrony, M., Elaboration of intermediate size planar proton conducting solid oxide cell by wet chemical routes: A way to industrialization, Solid State Ionics, 2015, 275: 97-100. Figure 1