Journal of Power Sources, Vol.195, No.17, 5534-5542, 2010
A possible solution to the mechanical degradation of Ni-yttria stabilized zirconia anode-supported solid oxide fuel cells due to redox cycling
The viability of cooling a solid oxide fuel cell (SOFC) during air exposure is investigated as a possible solution to the mechanical damage caused by inadvertent 'redox cycling' (cyclic exposure to air and then to H-2) of Ni-based anode-supported cells at high temperatures. In order to prevent electrolyte (and cell) cracking, it is shown that cooling the anode-supported Ni-YSZ samples during air exposure from 800 degrees C to <600 degrees C at rates >3 degrees C min(-1) significantly slows down the oxidation of Ni. This, in turn, minimizes the volume expansion due to NiO formation. Cell cooling rates of <3 degrees C min(-1) result in the cracking of the thin electrolyte layer, as sufficient time is then available for substantial NiO formation. It is also shown that partial oxidation during cool-down results in more extensive Ni oxidation in the outer regions of the anode layer compared to regions closer to the electrolyte. For the anode-supported cells investigated here, the electrolyte resists cracking when the nearby Ni particles (within 10-20 mu m of the electrolyte) are prevented from oxidizing to an extent of more than 65%. (C) 2010 Elsevier B.V. All rights reserved.
Keywords:Ni-YSZ anodes;Redox cycling;Ni oxidation;Solid oxide fuel cells;Cell cool-down;Electrolyte cracking