(621bk) Nanostructure Engineering of Nickelate Oxide Electrocatalysts for Enhanced Oxygen Exchange and Reduction Kinetics

The large overpotential losses induced by the sluggish cathodic oxygen reduction reaction (ORR) kinetics are one of the main challenges with developing intermediate temperature solid oxide fuel cells (IT-SOFCs). Current state-of-the-art cathode electrocatalysts used in these systems (such as La_1-xSr_xMnO_3-δ, LSM) exhibit low electrocatalytic activity for the oxygen reduction reaction at temperatures below 1073K. Nickelate oxides (e.g., La₂NiO_4+δ, LNO) have emerged as a promising class of materials for IT-SOFCs due to their high oxygen transport properties.[1] However, the mechanism governing the oxygen exchange and reduction on these oxides is still not fully understood and these materials have been mainly synthesized using techniques that lead to low surface areas.[2, 3]Our group has recently reported on a reverse microemulsion synthesis approach[4] that allows for control over the size and shape of nickelate oxides. We show for the case of La₂NiO_4+δ (LNO) that LNO nanostructures containing high concentration of (001)-Ni oxide terminated facets exhibit higher electrochemical activity toward oxygen exchange and reduction when compared to LNO structures with low energy facets. The electrochemical behavior of LNO nanorods and spheres is investigated by electrochemical impedance spectroscopy using symmetric electrochemical cells. A significant reduction in the area specific resistances (ASRs) of LNO-nanorod containing cells are observed as compared to cells containing LNO-spheres. Our results demonstrate the impact of utilizing well-defined nanostructured, mixed ionic and electronic electrocatalysts in enhancing the oxygen reduction kinetics in ceramic–based fuel cells.

References

[1] P.J. Gellings, H.J. Bouwmeester, Catalysis Today, 58 (2000) 1-53.

[2] J.M. Bassat, P. Odier, A. Villesuzanne, C. Marin, M. Pouchard, Solid State Ionics, 167 (2004) 341-347.

[3] G. Kim, S. Wang, A. Jacobson, C. Chen, Solid State Ionics, 177 (2006) 1461-1467.

[4] X. Ma, B. Wang, E. Xhafa, K. Sun, E. Nikolla, Chemical Communications, 51 (2015) 137-140.