A Highly Efficient Bifunctional Electrode Fashioned with In Situ Exsolved NiFe Alloys for Reversible Solid Oxide Cells
Junil Choi, Minho Kim, Song Kyu Kang, Jihoon Kim, Jungseub Ha, Hyun Ho Shin, Taiho Park, Won Bae Kim
Abstract
We developed a bifunctional electrode of Pr0.8Sr1.2(Fe,Ni)0.8Nb0.2O4−δ (R.P.PSFNNb) fashioned with in situ exsolved Ni-Fe alloy nanoparticles (NPs) for electrochemical oxidations of H2, CO, and syngas as well as CO2 electrolysis. The NiFe-R.P.PSFNNb was prepared by in situ phase transition of Pr0.4Sr0.6Fe0.8Ni0.1Nb0.1O3−δ (PSFNNb) along with exsolution of Ni-Fe alloys in a reducing atmosphere, as confirmed by X-ray diffraction and X-ray photoelectron spectroscopy (XPS) characterization. XPS and H2-temperature-programmed reduction analyses were also conducted to examine the behavior of the exsolution process. Transmission electron microscopy and electron energy loss spectroscopy element mapping concluded that the Ni-Fe alloy NPs were successfully exsolved and anchored on the parent oxide material. The NiFe-R.P.PSFNNb exhibited superior electrochemical performance for fuel electrode reactions of reversible solid oxide cells (RSOCs). A maximum peak power density of 829, 522, and 749 mW·cm–2 was obtained for the electrochemical oxidations of H2, CO, and syngas, respectively, and a high current density of −1.89 A·cm–2 was produced in the electrochemical reduction of CO2 to CO at a temperature of 850 °C. More interestingly, no significant degradation of the electrochemical performance was observed in both operating modes, indicating that the NiFe-R.P.PSFNNb proposed in this work could be a promising candidate as a bifunctional electrode for the practical implementation of RSOCs.