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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Merced Electronic Theses and Dissertations (2020)

In SOFCs, we observe that the porous electrodes tend to agglomerate and thus decrease the cell performance over time. The agglomeration (or sintering) of a porous oxide can be understood as the diffusion of the oxide atoms along the surface of a material to minimize the surface energy of the structure. Therefore, even an ultrathin overcoat is expected to deter the sintering process and thus maintain the porous geometry for longer period of time. In this thesis, the actual role of YSZ overcoat in the ORR process is presented through a series of electrochemical analyses. Without an overcoat, a nanoporous Pt is significantly agglomerated during a high-temperature operation, and ORR kinetics becomes limited by the availability of TPB. An ultrathin YSZ overcoat significantly suppressed the sintering kinetics and preserved the morphology of its underlying Pt layer. More importantly, the overcoat acts as an excellent facilitator of the atomic oxygen species-mediated chemical process(es), which used to be rate-limiting in the ORR of a non-coated Pt/YSZ system.

In the next step, to understand the impact of spincoated layer on the interface of cathode/electrolyte, EIS data obtained at different temperatures and oxygen partial pressures. Beside SEM imaging and XRD, to support the hypothesis of ORR kinetics, infiltration and ALD coating also performed on different samples. We found out that spin-coated layer has smaller nanoparticle sizes and 3~4 times smaller nanocrystalinity that increase the active cites for dissosiative adsorption on the cathode side, comparing to the available cites on bare LNF. EIS data along with ALD coating also strongly support the hypothesis that ion conducting pass through the LNFGDC FL playes an important role in decreasing the polarization resistance comparing the bare LNF cathode as well. It helps the available cites not limited to the vicinity of GDC interlayer but be available in entire FL and the ion transport to the GDC interlayer through GDC nanoparticles paths.

To sum up, a combination of nanoscale treatments including cathode infiltration, metal oxide ALD coating, and cathode-electrolyte interface spin-coating pursued to achieve a significantly enhanced performance and durability by addressing the issues. In addition, I also performed a systematic studies on the change in electrochemical kinetics and a possible shift of bottleneck process by the treatments to better understand the effect of each of this nano-functionalization on oxygen reduction catalysis process in SOFCs.

    Cover page: NANOSCALE FUNCTIONALIZATION OF SOFC CATHODE SURFACE AND INTERFACES
    • Article
    • Peer Reviewed
    LBL Publications (2019)
    High power density and longevity are required to commercialize solid oxide fuel cells for vehicular applications. In this work, electrochemical durability of high-performance metal-supported solid oxide fuel cells (MS-SOFCs) with infiltrated catalysts is investigated. Durability screening of various cathode and anode compositions is conducted. The Pr6O11 cathode and SDCN40 (40 vol% Ni-60 vol% SDC) anode are selected due to preferential tradeoff between performance and durability. X-ray diffraction indicates the catalyst phases are stable after prolonged thermal annealing. Electrochemical impedance and scanning electron microscopy analyses show that the evolution of SDCN40 is minimal, and coarsening and Cr poisoning of the Pr6O11 catalyst are the dominant degradation mechanisms. These degradation mechanisms are addressed by implementing three additional fabrication steps: (1) preoxidation of the metal support, (2) deposition of thin and protective atomic layer deposition (ALD) coatings throughout the cathode-side electrode and support, and (3) in situ pre-coarsening of the catalysts. A favorable tradeoff is achieved: the combination of the three fabrication steps reduces degradation rate at 0.7 V and 700 °C by two orders of magnitude to 2.3% kh−1, while sacrificing 35% of initial power density. The catalyst pre-coarsening step is primarily responsible for the loss of performance.
      Cover page: Progress in durability of metal-supported solid oxide fuel cells with infiltrated electrodes
      • Article
      • Peer Reviewed
      Energy Storage & Distributed Resources (2021)
      The authors regret that a technical mistake has been discovered, which impacts the current density and power density reported in this article. Briefly, the mistake was caused by catalyst solution leaking out of the intended 1 cm2 catalyzed area and depositing catalyst over the whole cell. As a result, the calculated current and power densities (total divided by the catalyzed area) were higher than reality because the measured current and power were dividing by the intended 1 cm2 instead of the actual area including the leakage, which was approximately 5 cm2. This issue is presented, analysed, and discussed in further detail in the supporting information of Reference 1. The authors would like to apologise for any inconvenience caused.
        Cover page: Corrigendum to progress in durability of metal-supported solid oxide fuel cells with infiltrated electrodes [Journal of Power Sources 437 (2019) 226935]
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