Engineering topics
Guan, Wanbing
Publications and source records attributed to Guan, Wanbing.
Activity and Stability of (Pr 1-x Nd x ) 2 NiO 4 as Cathodes for Solid Oxide Fuel Cells: Part V. In Situ Studies of Phase Evolution
This study is to complement an early report (the manuscript is attached for review purpose) on the role of interlayer on activity and performance stability in praseodymium nickelates. The aforementioned report showed a remarkable 48% increase in power density while switching from common GDC interlayer to a new interlayer chemistry (PGCO). Furthermore, a stable long-term performance was linked with suppressed reaction between the cathode and PGCO interlayer. In this article, we report in situ studies of the phase evolution. The high energy XRD studies at a synchrotron source showed fully suppressed phase transition in praseodymium nickelates with PGCO interlayer, while the electrodes on the GDC interlayer undergo substantial phase transformation. Furthermore, in operando and post-test XRD analyses shown fully suppressed structural changes in electrodes operated in full cells at 750°C and 0.80 V for 500 hours. SEM-EDS analysis showed that the formation of PrO x at the cathode-interlayer interface may play a role in a decrease of mechanical integrity of the interfaces, due to thermal expansion mismatch, leading to a local stress between the two phases. Furthermore, phase evolution at a narrow interface may propagate toward the electrode bulk, leading to structural changes Q1 and performance degradation.
In situ Studies of Phase Evolution in (Pr 1-x Nd x ) 2 NiO 4 Electrodes with Various Interlayer Chemistries
The interest in Pr2NiO4 (PNO) electrode stems from the necessity to develop active and stable oxygen electrodes (1-6) for solid oxide fuel cells (SOFCs) (7-9). PNO is known for its highly active nature (7,8,10), originating from its superior oxygen ion diffusion, surface exchange coefficient (2,7,9-11) and structural flexibility over a wide temperature region (from 500 to 900oC) (3,12). PNO electrode, however, does undergo structural evolution to form a higher order phase (Pr3Ni2O7) and Pr6O11 (PrOx) (8). The structural change has been a major concern because it possibly links with the performance degradation over long-term operation (7,8) Conventional x-ray diffraction (XRD) has been extensively used to investigate the structural evolution in nickelates in the form of powders or planar electrodes (8,10). This method has two major limitations due to its low flux and low resolution: (1) it might overlook the presence of additional phases in the system, which is especially true for praseodymium nickelates where XRD diffraction patterns of higher order phase(s) (e.g. Pr3Ni2O7) may overlap with the parent PNO phase, making quantification challenging (8); and (2) the quantification of phase evolution in electrochemically operated PNO electrode may show major structural change with almost 100% of the parent phase transition from the conventional XRD analysis, while the transmission electron microscopy (TEM) studies clearly show the regions of preserved PNO phase (7).
The Role of Interlayer on the Catalytic Activity and Performance Stability of (Pr 1-x Nd x ) 2 NiO 4 as Cathodes for Solid Oxide Fuel Cells
The use of doped ceria as an interlayer in solid oxide fuel cells (SOFCs) is ubiquitous, which provides a better thermal expansion match and prevents the interaction between cathode (e.g. LSCF) and electrolyte (e.g. YSZ). However, the role of ceria interlayer on the cathode phase durability, catalytic activity, and performance stability remains obscure. This is particularly true in nickelate cathodes (e.g. Pr2NiO4). In this work, the attention will be given to electrochemical properties in nickelate athodes with various interlayers. Two new interlayer designs were investigated including (1) a thin Pr6O11 film deposited on the surface of GDC and (2) a Pr-doped ceria interlayer. The latter design results in a 48% increase in cathode performance; and more importantly, it leads to zero degradation over long-term easurements. This is a tremendous improvement when compared to the performance degradation in cells with a GDC interlayer. The cathode-interlayer reaction was fully suppressed with PGCO, due to the intrinsic Pr enrichment in the interlayer, which contributed to suppressing the phase evolution in the electrode.
Probing Temperature Inside Planar SOFC Short Stack, Modules, and Stack Series
Not provided.
Activity and Stability of (Pr 1-x Nd x ) 2 NiO 4 as Cathodes for Solid Oxide Fuel Cells: II. Electrochemical Performance and Performance Durability
Single phase (Pr 1-x Nd x ) 2 NiO 4 cathode powders (x = 0, 0.25, 0.50, 0.75, and 1.0) were synthesized via a glycine-nitrate combustion and high temperature calcination. Anode supported cells were used to investigate the cathode property. A reproducible performance, within 9% for each cathode composition, was observed providing a wealth of data for quantitative studies. Area specific resistance analysis and i-V measurements between 650 and 850°C showed a decrease in the cell performance with increasing Nd content. Impedance spectrum analysis suggests that the decline in performance results from an increase in electrode polarization. While Pr 2 NiO 4 cells showed significant performance degradation of 6.40%/1,000 hours, the degradation rate for (Pr 0.75 Nd 0.25 ) 2 NiO 4 cells was reduced by an order of magnitude (0.56%/1,000 hours) with a 7% lower power output. Furthermore, the cathodes with a higher Nd content showed further improvement in performance stability with a marginal degradation rate of 0.06%/1,000 hours.