An effective approach to protect the Sm_0.5Sr_0.5Co_3-:δ (SSC) cathode from SO₂ in SOFCs

An issue associated with the use of Sm_0.5Sr_0.5Co_3-δ (SSC) as the cathode in SOFCs is the unexpected reactions between Sm or/and Sr and SO₂ from ambient air, forming a passivated layer on the surface of the SSC cathode and thus lowering the durability of the SSC cathode. Here, we develop four types of SSC cathode (SSC-particles, SSC-particles with Mg/Fe layer, SSC-nanofibers and SSC-nanofibers with Mg/Fe layer) and carry out four different cell tests with the four kinds of cathode to examine the durability of Sm_0.5Sr_0.5Co_3-δ (SSC) cathode when exposed to ambient air containing SO₂. SSC-particles and SSC-nanofibers are prepared by sol-gel method and electrospinning method, and Mg/Fe protective layer is infiltrated into SSC-particles and SSC-nanofibers to form the cathode with Mg/Fe layer, respectively. It is shown that after discharging with the ambient air containing SO₂, the microstructure and cathodic polarization resistances of all the four cathode are changed. More impressively, compared with the SSC-particles cathode, the use of the SSC-nanofibers cathode with Mg/Fe layer decreases the decline rate of current up to 50%. The significant improvement in the durability is mainly attributed to the fact that a specific network space of the nanofibers can make the Mg/Fe layer surround and run through the entire cathode, and the Mg/Fe layer will react with SO₂ first to protect the cathode. It is suggested that the combination of the nanofiber structure and the Mg/Fe protective layer is an effective approach to protect the SSC cathode from SO₂.