The degradation of Ni/yttria-stabilized zirconia (YSZ)-based solid oxide electrolysis cells operated at high current densities was studied. The degradation was examined at <mml:math display="inline"><mml:mrow><mml:mn>850</mml:mn><mml:mo>°</mml:mo><mml:mi mathvariant="normal">C</mml:mi></mml:mrow></mml:math>850°C , at current densities of −1.0, −1.5, and <mml:math display="inline"><mml:mrow><mml:mo>−</mml:mo><mml:mn>2.0</mml:mn><mml:mspace width="0.5em"></mml:mspace><mml:mi mathvariant="normal">A</mml:mi><mml:mo>/</mml:mo><mml:msup><mml:mrow><mml:mtext>cm</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>−2.0A/cm2 , with a 50:50 <mml:math display="inline"><mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mo>:</mml:mo><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math>(H2O:H2) gas supplied to the Ni/YSZ hydrogen electrode and oxygen supplied to the lanthanum, strontium manganite (LSM)/YSZ oxygen electrode. Electrode polarization resistance degradation is not directly related to the applied current density but rather a consequence of adsorbed impurities in the Ni/YSZ hydrogen electrode. However, the ohmic resistance degradation increases with applied current density. The ohmic resistance degradation is attributed to oxygen formation in the YSZ electrolyte grain boundaries near the oxygen electrode/electrolyte interface.

The electrochemical conversion of NO_x on non-impregnated and BaO-impregnated LSM15-CGO10 (La_0.85Sr_0.15MnO₃–Ce_0.9Gd_0.1O_1.95) porous cell stacks has been investigated, and extensive impedance analysis have been performed to identify the effect of the BaO on the electrode processes. The investigation was conducted in the temperature range 300–500 °C, a polarisation range from 3 V to 9 V and in atmospheres containing 1000 ppm NO, 1000 ppm NO + 10% O₂ and 10% O₂. On the non-impregnated cell stacks no NO_x conversion was observed under any of the investigated conditions. However, BaO impregnation greatly enhanced the NO_x conversion and at 400 °C and 9 V polarisation a BaO-impregnated cell stack showed 60% NO_x conversion into N₂ with 8% current efficiency in 1000 ppm NO + 10% O₂. This demonstrates high NO_x conversion can be achieved on an entirely ceramic cell without expensive noble metals. Furthermore the NO_x conversion and current efficiency was shown to be strongly dependent on temperature and polarisation. The impedance analysis revealed that the BaO-impregnation increased the overall activity of the cell stacks, but also changed the adsorption state of NO_x on the electrodes; whether the increased activity or the changed adsorption state is mainly responsible for the improved NO_x conversion remains unknown.

The problems of understanding the electrode reaction kinetics and in particular the degradation of the kinetics destroying the electrode performance, is briefly described. This is followed by an analysis of information that is needed and which knowledge may be acquired by available in operando and in situ techniques. The latter is illustrated by some examples. Further, it is discussed how research may be improved by refining and combining the available methods. Finally, possible research strategies are discussed.