To overcome the challenges posed by the mitigation of degradation modes, we have divided this theme into three scientific opportunities:
C1: Understanding and mitigating oxygen/electrolyte interface degradation.
The most common failure mode in solid oxide electrolysis cells is microstructural degradation near the oxygen electrode/electrolyte interface. Experimental results
indicate that multiple mechanisms are at play, all driven by the high effective oxygen chemical potential. Complete understanding of the degradation process requires detailed knowledge of the stress fields which will be achieved by developing an electrochemical model, coupled with thermomechanics, and validated through life-cycle experimental measurements and characterization.
C2: Understanding and mitigating fuel electrode degradation.
It has recently been shown that conventional Ni-YSZ fuel electrodes degrade due to the extremely low oxygen potentials produced by the applied electrolysis potential – under these conditions, zirconium from the zirconia phase can become dissolved in the metallic Ni phase, diffuse to more oxidizing regions, and then precipitate as zirconia particles. Other structural changes have been observed, such as migration of Ni out of the interfacial region. It appears that these fuel-electrode effects can be just as damaging as the oxygen-electrode effects. Experimental studies of these materials both by themselves and as electrodes in solid oxide cells will be carried out, using similar techniques as described in Opportunity C1. Theory will be critical to compliment the experimental work, by predicting oxygen potential phase stability diagrams, predicting oxygen vacancy formation/migration energies, and providing insights into the H2O dissociation and surface reaction mechanisms that are at the core of fuel electrode function. Therefore, DFT simulations will be closely coupled to the experimental work and calibrated against experimental data.
C3: Enhancing morphological stability of electrodes through rational design.
Reduced operating temperature SOECs provide a key pathway to high efficiency electricity conversion and storage. These so-called intermediate-temperature SOECs utilize electrodes designed with high interfacial surface areas to maximize oxygen transport and electrochemical reaction rates, but this also tends to make them unstable to coarsening and sintering, even at intermediate operating temperatures. Little is currently known about their long-term stability, but recent results show that they are critical. Experimentally,
accelerated life tests provide a means for developing combined electrochemical / coarsening models that can predict long-term performance.
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