Improving the fracture toughness of stabilized zirconia-based solid oxide cells fuel electrode supports: Effects of type and concentration of stabilizer(s)

Abstract

Further development and upscaling of the Solid Oxide fuel and electrolysis Cell (SOCs) technologies would significantly benefit from improvement of their mechanical robustness. In this work, microstructure, crystalline phase composition, fracture toughness and susceptibility to lowand high-temperature degradation of six different Ni(O)-Zirconia fuel electrode supports, manufactured from six different stabilized zirconia compounds, are investigated.In the oxidized state, tetragonal zirconia-based supports have higher fracture toughness than cubic zirconia-based substrate, due to the transformation toughening effect and a finer grained microstructure. The NiO-1.5CeO2 4.5YO1.5-SZ support exhibits the highest fracture toughness, showing a 30 and 10 % improvement compared to the state-of-the-art NiO-5.8YO1.5-SZ support at room temperature and 800 °C, respectively. In the reduced state on the other hand, the tetragonal and cubic zirconia-based substrates have comparable fracture toughness. The Ceria-Yttria codoped materials possess superior resistance to hydrothermal degradation due to the stabilizing effect of Ce 3+ formed during reduction.

Estimation of the effect of redox treatment on microstructure and tendency to brittle fracture of anode materials of YSZ–NiO(Ni) system

“…For YSZ-NiO ceramics in the as-sintered state (variant 1) this level is 3.75 MPa•m 1/2 , and for cermets (variants 2 and 3) it is 2.9 MPa•m 1/2 . These values are consistent with those obtained for such materials by traditional methods of fracture mechanics [6,40].…”

The Effect of Sintering Temperature on the Phase Composition, Microstructure, and Mechanical Properties of Yttria-Stabilized Zirconia

“…It is critically important to manufacture materials resistive to the aggressive operating environment [35][36][37][38] to avoid microstructure degradation [39][40][41][42]. Therefore, along with strength and tribology tests of materials as the most popular methods for diagnosing their load-bearing capacity, the indentation test, known as the simplest mechanical method [39,43], is widely used. This method is more microstructurally sensitive as compared to the above-mentioned ones and allows for estimating the crack growth resistance of materials [40,44].…”

Strength and hydrothermal stability of NiO–stabilized zirconia solid oxide cells fuel electrode supports

“…Works investigating the hydrothermal degradation issue in porous NiO-SZ SOCs supports are still rare. In our previous work [11], we observed the susceptibility of fuel electrode supports in reduced state to hydrothermal degradation. The LTD was less pronounced in the co-doped samples because of the increased stabilizing effect of Ce 3+ over Ce 4+ , formed during the reduction of the supports.…”

“…The transformation toughening effect decreases markedly by increasing temperature. As a result, the fracture toughness of NiO-3YSZ decreases at 800 °C (typical operating temperature of SOCs), yet remains higher than NiO-8YSZ [6,11]. Compared to yttria (Y) doped zirconia, ceria (Ce) doped zirconia ceramics possess a higher fracture toughness and resistance to hydrothermal degradation but a lower strength [12,13].…”

“…Effects of lowering stabilizer content on improving the mechanical properties of stabilized tetragonal zirconia ceramics is well investigated in literature [10,12], but applying this approach for SOCs components and its consequences is not well explored. In our previous work [11], we investigated the fracture toughness of SOCs supports made of six different zirconia compounds: the above-mentioned compounds (3YSZ and 8YSZ) together with four other tetragonal zirconia materials (Y doped and Ce-Y co-doped) having lower stabilizer concertation than 3YSZ. A Ce-Y co-doped material, co-doped with 1.5 mol% CeO2 and 4.5 mol% YO1.5 was found to possess the highest fracture toughness, up to 30 % higher compared to the-state-of-the-art (NiO-3YSZ).…”