Three-Dimensional NiO-Decorated La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ Nanofibrous Mesh as High-Performance Cathode for Protonic Ceramic Electrochemical Cells

For commercialization of a solid oxide fuel cell, it is vital to develop cathode materials with optimal microstructure in order to overcome the trade-off between lower operation temperature and higher oxygen reduction reaction (ORR) rate and conductivity. In this work, we design and synthesize cost-effective La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) nanofibers decorated with uniformly distributed NiO nanoparticles as the cathode of protonic ceramic electrochemical cells. With an appropriate NiO decoration to tune the ORR activity and hierarchical microstructure of LSCF nanofibers, the three-dimensional (3D) NiO-LSCF nanofibrous mesh cathode exhibits significantly higher peak power density than that with a bare LSCF nanofiber mat cathode in solid oxide fuel cell (SOFC) tests. The reduced ohmic and polarization resistances caused by NiO incorporation can be attributed to the increased connectivity in the LSCF 3D mesh due to enhanced sintering at contacts between nanofibers, which facilitates oxygen ion and electron transports, and the uniformly distributed NiO nanoparticles over the LSCF nanofiber surface, which increases the ORR activity. Furthermore, when operated in solid oxide electrolysis cell (SOEC) mode, a current density of −780 mA/cm² with a faradaic efficiency of 69% is obtained at 800 °C with the 15 wt % NiO-decorated LSCF 3D mesh. All these findings show that the combination of mixed ionic-electronic conductor (MIEC) 3D mesh and its surface decoration with nanoparticles of high ORR activity can effectively boost the performance of P-SOFCs and SOECs.