Degradation Mechanisms of Solid Oxide Fuel Cells under Various Thermal Cycling Conditions.

A critical issue to tackle before successful commercialization of solid oxide fuel cells (SOFCs) can be achieved is the long-term thermal stability required for SOFCs to operate reliably without significant performance degradation despite enduring thermal cycling. In this work, the impact of thermal cycling on the durability of NiO-yttria-stabilized zirconia-based anode-supported cells is studied using three different heating/cooling rates (1, 2, and 5 °C min-1) as the temperature fluctuated between 400 and 700 °C. Our experiments simulate time periods when power from SOFCs is not required (e.g., as might occur at night or during an emergency shutdown). The decay ratios of the cell voltages are 8.8% (82 µV h-1) and 19.1% (187 µV h-1) after thermal cycling testing at heating/cooling rates of 1 and 5 °C min-1, respectively, over a period of 1000 h. The results indicate SOFCs that undergo rapid thermal cycling experience much greater performance degradation than cells that experience slow heating/cooling rates. The changes in total resistance for thermally cycled cells are determined by measuring the Rpol of the electrodes (whereas the ohmic resistances of the cells remain unchanged from their initial value), signifying that electrode deterioration is the main degradation mechanism for SOFCs under thermal cycling. In particular, fast thermal cycling leads to severe degradation in the anode part of SOFCs with substantial agglomeration and depletion of Ni particles seen in our characterizations with field emission-scanning electron microscopy and electron probe microanalysis. In addition, the mean particle size in the cathode after thermal cycling testing increases from 0.104 to 0.201 µm for the 5 °C min-1 cell. Further, the presence of Sr-enriched regions is more significant in the La0.6Sr0.4Co0.2Fe0.8O3-δ cathode after fast thermally cycled SOFCs.

Utilizing the Intrinsic Thermal Instability of Swedenborgite Structured YBaCo4O7+δ as an Opportunity for Material Engineering in Lithium-Ion Batteries by Er and Ga Co-Doping Processes.

We firstly introduce Er and Ga co-doped swedenborgite-structured YBaCo4O7+δ (YBC) as a cathode-active material in lithium-ion batteries (LIBs), aiming at converting the phase instability of YBC at high temperatures into a strategic way of enhancing the structural stability of layered cathode-active materials. Our recent publication reported that Y0.8Er0.2BaCo3.2Ga0.8O7+δ (YEBCG) showed excellent phase stability compared to YBC in a fuel cell operating condition. By contrast, the feasibility of the LiCoO2 (LCO) phase, which is derived from swedenborgite-structured YBC-based materials, as a LIB cathode-active material is investigated and the effects of co-doping with the Er and Ga ions on the structural and electrochemical properties of Li-intercalated YBC are systemically studied. The intrinsic swedenborgite structure of YBC-based materials with tetrahedrally coordinated Co2+/Co3+ are partially transformed into octahedrally coordinated Co3+, resulting in the formation of an LCO layered structure with a space group of R-3m that can work as a Li-ion migration path. Li-intercalated YEBCG (Li[YEBCG]) shows effective suppression of structural phase transition during cycling, leading to the enhancement of LIB performance in Coulombic efficiency, capacity retention, and rate capability. The galvanostatic intermittent titration technique, cyclic voltammetry and electrochemical impedance spectroscopy are performed to elucidate the enhanced phase stability of Li[YEBCG].

Operation Protocols To Improve Durability of Protonic Ceramic Fuel Cells.

To develop reliable and durable protonic ceramic fuel cells (PCFCs), the impacts of the operation protocols of PCFCs on the cell durability are investigated through analyses of the main degradation mechanisms. We herein propose three appropriately designed control protocols, including cathode air depletion, shunt current, and fuel cell/electrolysis cycling, to fully circumvent the operating-induced degradation of PCFCs. For this purpose, anode-supported cells, comprised of a NiO-BaCe0.7Zr0.1Y0.1Yb0.1O3-δ anode, BaCe0.7Zr0.1Y0.1Yb0.1O3-δ electrolyte, and NdBa0.5Sr0.5Co1.5Fe0.5O5+δ-Nd0.1Ce0.9O2-δ composite cathode, are prepared, and their long-term performances are evaluated under a galvanostatic condition of 0.5 A·cm-2 at 650 °C. The cell voltages of the protected cells using the operation protocols to prevent performance degradation are stably maintained under the applied current density for more than 1200 h without any noticeable degradation, whereas the performance of the unprotected cell gradually decreased with time, and the decay ratio was 14.9% over 850 h. The significant performance decay of the unprotected cell is strongly associated with the cathode degradation phenomenon, which was caused by the water vapor continuously produced during the electrochemical reactions. Hence, the performance recovery of the PCFCs with the operation protocols is achieved by incrementally decreasing the cathode potential (close to a value of zero) to minimize the effect of high PH2O and PO2 during the PCFC operations.