High durability of La_0.6Sr_0.4Co_0.2Fe_0.8O_{3−δ}/samaria-doped ceria (SDC) composite oxygen electrode with SDC interlayer for reversible solid oxide fuel cell/solid oxide electrolysis cell

Abstract

We have examined the long-term durability of a La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3¹¤ (LSCF)samaria-doped ceria (SDC) composite oxygen electrode with SDC interlayer for reversible solid oxide cells (R-SOCs). A symmetrical cell with the configuration: LSCF SDC«SDC interlayer«yttria-stabilized zirconia (YSZ) electrolyte«SDC interlayer«LSCFSDC, was operated at 900°C and a constant current density of 0.5 A cm ¹2 with the top electrode as the anode (O 2 evolution). The IR-free overpotentials at both the anode and cathode were virtually constant during 5500 h of operation. The value of ohmic resistance at the anode side (R A ) increased slightly, whereas that at the cathode side (R C ) increased markedly. The IE performance of the bottom electrode (operated as the cathode), that was measured from ¹1.0 to 1.0 A cm ¹2 every 1000 h, degraded specifically at high current densities. It was found that the thickness, pore size, and porosity in both electrodes were unchanged, but the distribution of the Sr component changed markedly at both the LSCFSDC/SDC interlayer and SDC interlayer/YSZ interfaces. While the diffusion of the Sr component from the anode was limited within the SDC interlayer, the Sr component from the cathode reached the SDC interlayer/YSZ interface, which could increase the R C , likely due to the formation of SrZrO 3 . However, the diffusion rates of Sr were found to be noticeably slowed down at dense portions of the SDC interlayer. Hence, it is essential to prepare a dense, uniform SDC interlayer to improve both the durability and performance of R-SOCs.

Surface Segregation in Solid Oxide Cell Oxygen Electrodes: Phenomena, Mitigation Strategies and Electrochemical Properties

“…To clarify the effects of polarization current direction on the activity of LSC-based electrodes, Shimura et al [152] studied symmetric LSCF-SDC composite electrodes on YSZ electrolytes with dense SDC barrier layers under polarization at 900 °C and 0.5 A cm −2 for 5500 h. Here, these researchers reported that the overpotentials under anodic and cathodic modes remained constant over the operational duration in which the cell ohmic resistance increased from 0.5 to 0.8 Ω cm 2 after cathodic polarization, whereas the increase after anodic polarization was very small. Elemental analysis further showed significant Sr accumulation at the YSZ/SDC interlayer interface after cathodic polarization, which was consistent with cell ohmic resistance increases under cathodic polarization.…”

Changes in Microstructure of Ni–Co Dispersed Samaria-Doped Ceria Hydrogen Electrodes for the Improved Durability via Reversible Cycling Operation of Solid Oxide Cells

“…1 μm). 16,17 An air reference electrode (ARE) was prepared by wrapping a Pt wire around the periphery of the YSZ electrolyte disk with Pt paste.…”

“…8,12,13 The degradation mechanism of the oxygen electrodes observed in both operation modes has been clarified, i.e., unfavorable solid-state reactions between the perovskite-oxides and the YSZ electrolyte through interlayer defects (or grain boundaries) and electrode delamination. [13][14][15][16][17] In contrast, the mechanism for the degradation of the Ni-YSZ cermet electrode for the hydrogen evolution reaction (HER) in the SOEC mode has remained unclear. 14,15,18,19 For Ni-YSZ cermet electrodes, a depletion of Ni close to the electrode/YSZ electrolyte interface has been reported, specifically, at high current densities (or high overpotentials), in addition to segregation of impurities (such as Si) at the triple phase boundary (TPB) and/or agglomeration of Ni.…”

“…8,13,18,19 We have engaged in the research and development of highperformance electrodes with novel architecture for the R-SOC. 16,17,[20][21][22][23][24][25][26][27][28][29] Very recently, we found that the durability of a double-layer H 2 (DL) electrode, consisting of a SDC scaffold [samaria-doped ceria (CeO 2 ) 0.8 (SmO 1.5 ) 0.2 ] with highly dispersed Ni 0.9 Co 0.1 nanoparticles as the catalyst layer (CL) and a thin current-collecting layer (CCL) of Ni-YSZ cermet, was greatly improved via reversible cycling operation between the SOEC and SOFC-modes. 28 In the present work, we focus on the stabilization mechanism of the microstructure of the CL in our H 2 electrode via reversible cycling operation.…”

Synthesis and Evaluation of Ni Catalysts Supported on BaCe0.5Zr0.3−xY0.2NixO3−δ with Fused-Aggregate Network Structure for the Hydrogen Electrode of Solid Oxide Electrolysis Cell

“…The set-up for the test cell was described in Shimura and coworkers report [44]. The test cell was sealed with a gold ring.…”