The Effect of Hydrogen Concentration on the High-Temperature (600 °C) Reduction Performance and Strength of YSZ–NiO(Ni) Anode Material for Solid Oxide Fuel Cells

A ceramic material based on yttria-stabilized zirconia and nickel oxide (YSZ–NiO) is widely used for the fabrication of solid oxide fuel cell (SOFC) anodes. To make such an anode ready for operation in a SOFC, corresponding treatment in a reducing atmosphere should be performed ensuring NiO to Ni reduction that provides electrical conductivity of the anode. This work aims to study the effect of hydrogen concentration on the high-temperature (600 °C) reduction performance and strength of YSZ–NiO(Ni) anode material. To obtain the corresponding YSZ–NiO(Ni) cermet structures, a series of YSZ–NiO ceramic specimens were reduced in various hydrogen-containing atmospheres for 4 h at 600 °C under a pressure of 0.15 MPa. The atmospheres were as follows: (i) Ar–5 vol% H2 mixture; (ii) pure hydrogen (99.99 vol% H2). After reduction, mechanical behavior of specimens was studied. Three different mechanical tests were performed: Vickers microhardness test, fracture toughness test by indentation method, and flexural strength test under three-point bending. Microstructure of the cermets and fracture surface morphology of the specimens that underwent the strength test were studied using scanning electron microscopy. It was found that Ar–5 vol% H2 mixture provided slow reduction of ceramic specimens with the formation of thin fringes that cover nickel oxide particles. Exposure for 4 h at 600 °C in this atmosphere did not ensure the complete reduction of the nickel phase particles. In contrast, specimens reduced in pure hydrogen exhibited distinct microstructure of completely reduced nickel particles. Energy dispersive X-ray microanalysis showed a slight sign of nickel oxide in this cermet. However, comparatively low flexural strength, Vickers microhardness, and fracture toughness were determined for this material. In comparison, these mechanical characteristics were found to be higher for the cermet reduced in Ar–5 vol% H2 mixture.