Abstract
The objective of this paper is to manufacture free-standing solid oxide cells (SOCs) through the atmospheric plasma spray process (APS), without the aid of a metallic support nor the need for a post-process heating treatment. A five-layered cell was fabricated. Fused and crushed yttria-stabilized zirconia (YSZ) powder in the 5–22 μm particle size range was used in order to achieve a dense electrolyte layer, yet still permitting satisfactory ionic diffusivity. Nickel oxide (NiO) powder that was obtained by in-house flame spray (FS) oxidation of pure nickel (Ni) powder was mixed and sprayed with the original Ni-YSZ feedstock, so as to increase the porosity content in the supporting electrode. Two transition layers were sprayed, the first between the support electrode and the electrolyte (25% (Ni/NiO)–75% YSZ) and the second at the electrolyte and the end electrode interface (50% YSZ–50% lanthanum strontium manganite (LSM)). The purpose of intercalation of these transition layers was to facilitate the ionic motion and also to eliminate thermal expansion mismatches. All the as-sprayed layers were separately tested by an in-house developed acetone permeability comparative test (APCT). Electrodes with adequate porosity (25–30%) were obtained. Concerning electrolytes, relatively thick (150–200 µm) layers derived from fused and crushed YSZ were found to be impermeable to acetone, while thinner YSZ counterparts of less than 100 µm showed a low degree of permeability, which was attributed mostly to existent microcracks and insufficient interparticle cohesion, rather than to interconnected porosity.
Highlights
Solid oxide cells (SOC), namely solid oxide fuel cells (SOFC) and solid oxide electrolysis cells (SOEC), are environmentally friendly power-generation systems via conversion of energy from one form to another
(150–200 μm) layers derived from fused and crushed yttria-stabilized zirconia (YSZ) were found to be impermeable to acetone, while thinner YSZ counterparts of less than 100 μm showed a low degree of permeability, which was attributed mostly to existent microcracks and insufficient interparticle cohesion, rather than to interconnected porosity
Nature and size range—were carried out in order to control porosity in the YSZ
Summary
Solid oxide cells (SOC), namely solid oxide fuel cells (SOFC) and solid oxide electrolysis cells (SOEC), are environmentally friendly power-generation systems via conversion of energy from one form to another. SOEC is a reverse SOFC that uses electrical energy in order to achieve water electrolysis and consequent hydrogen production. A necessary step during electrolyte manufacture, and at the same time a major disadvantage of most of the above techniques, is the subsequent sintering of the electrolyte layer in order to achieve dense microstructures and optimum ion conductivity. Such processes lead to vast amounts of energy consumption, increased process time and elevated final cost of the product. Other difficulties that arise, related to high-temperature SOC counterpart construction, are interfacial diffusion at the electrode/electrolyte interface and thermal stresses due to mismatch in thermal expansion coefficients of the layers, followed by mechanical damage [4]
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