Electrochemical Performance of Plasma Sprayed Metal Supported Planar Solid Oxide Fuel Cells

Abstract

High material and production costs are key barriers to the widespread commercialization of solid oxide fuel cells (SOFCs). Thermal spray techniques are a low cost alternative for the production of SOFCs. The objective of this work was to fabricate single cells by thermal spraying and to evaluate the impact of electrolytes and anodes, differing in terms of thickness, composition and microstructure, on the cell performance. In this work, the anode layer was deposited on a planar ferritic steel support with in-plane dimensions 50 mm X 50 mm, thickness of 550 µm and 35-40% porosity by atmospheric plasma spraying (APS). The anode material consisted of nickel, yttria stabilized zirconia (YSZ) and a pore former. The anode layer thickness was around 60 µm. The electrolyte layer was deposited by a low pressure plasma spray technique called plasma spray-thin film (PS-TF) which can produce dense coatings at high deposition rates. The electrolyte material consisted of 3YSZ and 8YSZ consisting of different powder morphologies such as fused and crushed and agglomerated and sintered. In order to ensure sufficient gas tightness, electrolytes thicknesses of 50-90 µm were deposited. The cathode layer was screen-printed and sintered in-situ during the start-up of the electrochemical tests. The cathode material was La0.58Sr0.4Co0.2Fe0.8O3-δ (LSCF). It must be noted that no diffusion barrier layer was deposited between the YSZ electrolyte and the LSCF cathode which will affect the performance and stability of the cells. The electrochemical tests were performed in a temperature range of 600-800°C at atmospheric pressure under various gas compositions of H2, H2O and N2 on the anode side and of O2 and N2 on the cathode side while keeping the total gas flow constant. Current-voltage characteristics and impedance spectra were measured. Porous anodes and dense electrolytes were achieved in all cases. The measured open cell voltage indicated acceptable electrolyte gas tightness. Power density of produced cells at an operating voltage of 0.7 V were measured as high as 600 mW/cm2. In this work, the impact of spray parameters and applied layer thicknesses on the gas tightness of the electrolyte and the area specific resistance of the cell will be discussed. Keywords: plasma spraying, solid oxide fuel cells, electrochemical characterization, impedance spectroscopy