Solid oxide cells are electrochemical devices used for the conversion of chemical energy to electrical energy (Solid Oxide Fuel Cells-SOFC) and vice versa (Solid Oxide Electrolysis Cells-SOEC). ...However, long-term performance degradation impedes the widespread commercialization of the technology. To investigate the effects of operation mode on the degradation of Ni/yttria-stabilized zirconia (YSZ) electrodes, two cells from the same production batch are tested for 1000 h at 800 °C; one as SOFC and the other as SOEC. The cells are fed with the same gas composition at the fuel inlet side (p(H2O)/p(H2) = 0.5/0.5) while the direction of the current (±1 A cm−2) is reversed. It is found that Ni coarsening occurs to a similar extent in both operation modes while Ni depletion is only observed in SOEC mode, in the region close to the electrode/electrolyte interface. Here, the Ni/(Ni + Zr + Y) atomic ratio decreases from ~0.49 before operating the cell to ~ 0.28 and the SOEC shows a pronounced decrease in percolating triple phase boundaries (TPBs). The wettability of Ni on YSZ is studied and hypotheses are presented to correlate the phenomena of Ni coarsening and Ni depletion with the cell operation mode.
•The effect of the operation mode (SOEC, SOFC) on SOC degradation was investigated.•Ni coarsening occurs regardless of the SOC operation mode.•Ni depletion at the electrode/electrolyte interface is observed only in SOEC mode.•Ni depletion is a major cause of SOEC performance degradation.•A gradient in Ni/YSZ contact angle as the main driving force for Ni depletion.
Ni coarsening in the Ni/yttria-stabilized zirconia (YSZ) fuel electrode of solid oxide cells (SOCs) is a major cause of long-term performance degradation. Phase-field modeling is a powerful tool for ...studying Ni coarsening in the complex 3D structures of SOC fuel electrodes. In this work, we present a study aimed at validating a phase-field model, comparing simulation results with time-dependent ex-situ tomographic data. Three equilibrium Ni/YSZ contact angles are examined: 97°, 120°, and 150°. Simulated microstructures are characterized through quantities such as the Ni mean radius, triple-phase boundaries, and interface shape distribution. The phase-field model reproduces the improved pore connectivity in the first stage of Ni coarsening observed in the tomography data. This model also indicates that the contact angle plays a key role in the microstructural evolution during Ni coarsening, and the best match to the experiment was obtained with the equilibrium contact angle of 120º, close to a measured value in literature. Finally, the limitations of the model are discussed.
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The effects of long-term operation in electrolysis mode on the microstructure of Ni/YSZ electrodes were investigated. The electrode structures were investigated in "as reduced" state and after 9000 h ...of operation in a 25 cell stack. Microstructural data were obtained by scanning electron microscopy and focused-ion-beam serial sectioning. Microstructural characteristics were extracted by 1D and 3D methods. Significant microstructural changes were observed between the two cells analyzed. A significant loss of Ni in the active electrode is observed, from ~ 29% (by volume) in the reference cell to ~ 24% as well as a coarsening of the Ni particle sizes. The long-term tested cell shows lower percolating triple phase boundary density (0.76 µm/µm3) than the un-tested reference (2.0 µm/µm3). This reduction is mainly due to the loss of triple phase boundary percolation through the Ni phase where a reduction from a percolation degree above 90% to ~50% is observed.
Long-term operation strongly affects the microstructure of Ni/YSZ cermets used in state of the art fuel electrodes for solid oxide cells. The microstructural changes are considered to heavily affect ...the cell degradation. In this paper, the characterization of the Ni/YSZ electrode of a solid oxide electrolysis cell tested as part of a stack tested for 1 year was performed through focused ion beam-scanning electron microscopy and energy dispersive X-ray spectroscopy. A reference cell and two locations of interest in the tested cell were selected: one at the steam inlet side and the other at the outlet. Considerable microstructural changes were observed in the tested cell compared to the reference cell and between the inlet and outlet side. A decrease in Ni (from 30% in the reference cell to 24% in the tested cell), and in percolating triple phase boundaries length (from 2.83 μm/μm3 in the reference cell to 0.76 μm/μm3 in the tested cell) was observed in the active fuel electrode. Based on the results of this work and previous studies we hypothesize that the degradation trend between different operating conditions at the inlet and outlet of the cell is related to the current redistribution inside the cell.
In early 2015, the Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) provided notification of outbreaks of transmission of carbapenem-resistant ...Enterobacteriaceae (CRE) associated with the use of duodenoscopes in endoscopic retrograde cholangiopancreatograhy (ERCP). In August of 2015, the FDA released supplemental duodenoscope reprocessing measures from an FDA-led expert panel. A multidisciplinary team was established to implement duodenoscope microbiological culturing following duodenoscope reprocessing at our institution, a community based hospital.
In June 2015 a Field Safety Notice was sent from the manufacturer of the heater-cooler unit (HCU) used for cardiothoracic procedures. The notice was in response to an investigation of non-tuberculous ...mycobacterium (NTM) infections in cardiothoracic surgical patients.
Attitudes towards Information Technologies (IT) of mainstream Social Science faculty, known for their recalcitrance to Information Technology, were shown to impact IT use based on a sample of 91 ...young predominantly male highly educated faculty throughout Florida. From explanacist point of view productivity, the degree to which participants find IT efficient was found to be a good predictor of IT use. While faculties had favorable attitudes towards using IT and were trained on using computers use of IT remains low. The predominant approach to teaching strategy, instructional design, with its emphasis on rhetorical transmission of information dispensed by authority combined with logistical, epistemological, student preparation, integration and assessment barriers diminish the need for integrating IT into teaching and learning. Under this scenario it is unlikely that use of IT in instruction will grow volitionally. In a population preferring to exercise personal control using tools that are extensions of their organism discontinuous change may be necessary to become more robustly adaptive to an environment requiring faculty to be proficient in the use of IT and its integration into instruction. Enablers of use of IT in instruction should include constructivist approaches to teaching and the adoption of strategies from learning organizations. Faculty should continue to take responsibility for what and how students learn. Bilateral communication between teacher and student will remain higher education's predominant feature to nurture learning. The delivery infrastructure should support it, not be in the foreground.
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