The influence of electrodes on the strength of planar zirconia solid oxidefuel cells

The strength of symmetric anode/electrolyte/anode and cathode/electrolyte/c athode planar multiple electrode assemblies (MEAs), fabricated by screen pr inting electrodes onto pre-fired tape-cast electrolyte plates was measured in biaxial flexure. The electrolyte was Zr0.84Y0.16O1.92 (YSZ), the anode N iO/YSZ and the cathode La0.75Sr0.2MnO3-delta. The residual stress in the el ectrodes was estimated by curvature measurement after removal of one electr ode. The residual stress in the anodes was very low (11 MPa) due to stress relief by extensive channel cracking. The residual stress in the cathodes w as much higher (39 MPa) and was in reasonable agreement with the expected t hermoelastic stress. The applied load at failure, and the stress in the ele ctrolyte at failure (343 MPa), for anode MEAs were almost equal to those of electrolyte plates (374 MPa). This is consistent with the low residual str ess and observed crack deflection by delamination at the anode/electrolyte interface. The applied load at failure, and the stress in the electrolyte a t failure (182 MPa), for cathode MEAs were much lower. This is partially ex plained by the residual stress in the cathode acting to increase the applie d stress intensity at defects in the electrolyte, but this effect is not la rge enough to explain fully the reduced strength. (C) 2001 Kluwer Academic Publishers.