Abstract
Herein, electroreduction in yttria-stabilized zirconia are investigated by means of Hebb-Wagner polarization experiments. By performing optical and thermal microscopy on single crystals and thin films during the application of an electric field under vacuum or oxygen-tight sealed conditions, the movement of the reduction front from the cathode to the anode, which causes a blackening of the material, is monitored. When performing electrocoloration experiments on thin film samples, the progressing reaction of the blackened region was found to be inhomogeneous and evolves as a dendrite-like finger structure. The progression of the blackening fingers follow preferentially the electric field lines and thus are influenced by distortions in the field that can be caused by metallic particles embedded in the oxide. In contrast to this, in the first stage of the reduction process no significant influence of mechanically-induced dislocations on the morphology or kinetics on the electroreduction can be found. Only after a heavy electroreduction was a localized transformation of the surface region observed. There is an evolution of highly oxygen deficient ZrOx regions, which have a characteristic checked topography pattern at the microscale level.
Highlights
The emissions-free energy system of the future depends on the efficient storage of energy
Short electroreduction in single crystals In order to follow the electroreduction in yttria-stabilized zirconia (YSZ) single crystals, we deposited two oblong Pt electrodes on the surface, which were separated by 3 mm from each other
Comparable experiments on YSZ revealed that the blackening fingers mainly follow the electric field lines and are influenced by distortions of the field distribution as can be caused by metallic microparticles acting as electric dipoles
Summary
The emissions-free energy system of the future depends on the efficient storage of energy. Solid oxide fuel cells (SOFCs), employing the reaction of oxygen and hydrogen to form water, have been identified as highly reliable and costeffective energy converters [1]. They can be operated as solid oxide electrolysis cells (SOECs) producing hydrogen by water-splitting and offering a complete solution for the conversion of electrical to chemical energy and vice versa [2]. It has become apparent that when operating such a cell in the electrolysis mode, degradation effects can occur, which eventually limit the device’s lifetime [3,4,5]. The investigation of the solid ion conductors that are used as SOEC electrolytes under the gradients of electrical potential is of highly relevant
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