Stability and Activity of (Pr_1‐xNd_x)₂NiO₄ as Cathodes for Solid Oxide Fuel Cells: I. Quantification of Phase Evolution in Pr₂NiO₄

Abstract

Praseodymium nickelate (Pr2NiO4) is an active oxygen electrode for solid oxide fuel cells, but undergoes phase transition at elevated temperatures (e.g., 750°C). Quantification of this phase evolution in an operating single cell is challenging because of the overlap of X‐ray diffraction (XRD) peaks between the cathode and oxide current collector. In this work, we replace the oxide current collector with a gold metal grid, circumventing these challenges by allowing the exposure of the cathode to the X‐ray beam, while eliminating peak overlap. Quantification of the phase evolution was performed by a least‐squares fitting of the linear combination of XRD standards against the experimental patterns. Energy‐dispersive spectroscopy analysis on long‐term operated cells showed the absence of reactions between the gold grids and the cathodes. Additionally, the grids exhibited excellent mechanical stability under operating conditions and enabled similar cell performance as an oxide current collector.

Activity and Stability of (Pr1-xNdx)2NiO4as Cathodes for Solid Oxide Fuel Cells

“…current density, which is consistent with our previous measurements on PNO electrodes. [3][4][7][8] With an increase in Nd content, the overall cell performance decreases. For instance, the power densities at 0.7 V at 750…”

“…This can be attributed to relatively fast phase evolution in PNO. 8 For cells with Nd substituted cathodes, the degradation rates are relatively constant. An unexpected increase in initial cell performance (2-3%) was observed within first 125 hours of operation in cells with platinum current collector.…”

“…8 PNO partially decomposes to praseodymium oxide (PrO x ) and a higher order layered structure (Pr 3 Ni 2 O 7 ) during operation, 8 which presents a concern because of possible structural collapse and longterm performance degradation. 4,8 Current approaches to stabilize the PNO phase focus on substituting A and/or B-site ions.9,10 Both La 2 NiO 4 and Nd 2 NiO 4 (NNO) are more stable than PNO, 11 but have lower power density.12 This work reports an attempt to stabilize the long-term cell performance in praseodymium nickelate. (Pr 1-x Nd x ) 2 NiO 4 (PNNO, x = 0, 0.25, 0.50, 0.75, and 1.0) cathodes were synthesized and electrochemically evaluated in anode supported cells.…”

“…The electrochemical performance of PNO, however, did show an appreciative degradation 4 which likely resulted from its readily occurring phase transitions at operating conditions. 8 PNO partially decomposes to praseodymium oxide (PrO x ) and a higher order layered structure (Pr 3 Ni 2 O 7 ) during operation, 8 which presents a concern because of possible structural collapse and longterm performance degradation. 4,8 Current approaches to stabilize the PNO phase focus on substituting A and/or B-site ions.…”

“…8 PNO partially decomposes to praseodymium oxide (PrO x ) and a higher order layered structure (Pr 3 Ni 2 O 7 ) during operation, 8 which presents a concern because of possible structural collapse and longterm performance degradation. 4,8 Current approaches to stabilize the PNO phase focus on substituting A and/or B-site ions.…”