Increased Cathodic Kinetics on Platinum in IT-SOFCs by Inserting Highly Ionic-Conducting Nanocrystalline Materials

Abstract

One of the crucial factors for improving intermediate-temperature solid oxide fuel cell (SOFC) performance relies on the reduction in the activation loss originating from limited electrode reaction kinetics. We investigated the properties and functions of the nanocrystalline interlayer via quantum simulation and electrochemical impedance analyses. Electrode impedances were found to decrease several folds as a result of introducing a nanocrystalline interlayer and this positive impact was the most significant when the interlayer was a highly ionic-conducting nanocrystalline material. Both exchange current density and maximum power density were highest in the ultrathin SOFCs (fabricated with microelectromechanical systems (MEMS) compatible technologies) consisting of a 50 nm thick nano-gadolinia doped ceria (GDC) interlayer. Oxygen vacancy formation energies both at the surface and in the bulk of pure zirconia, ceria, yttria-stabilized zirconia, and GDC were computed from density functional theory, which provided insight on surface oxygen vacancy densities.

First Principles Study of Oxygen Incorporation Reactions in Oxides

“…However, the trend is clear-vacancies form more readily in CeO 2 and GDC than in YSZ or ZrO 2 . This conclusion is supported by experimental scanning tunneling spectroscopy evidence [31] and by Huang's result that a YSZ|GDC bilayer electrolyte with a layer of GDC near the cathode performs better than an electrolyte with only YSZ [32]. Fe may play a role in establishing the wide window of non-stoichiometry allowed in these materials, which is very helpful for oxygen incorporation.…”

Effects of Grain Boundaries at the Electrolyte/Cathode Interfaces on Oxygen Reduction Reaction Kinetics of Solid Oxide Fuel Cells

“…10,12,14,17,25 High-resolution chemical analysis, performed by using STEM-EDS, showed higher concentrations of dopant cations at the GBs of YSZ and GDC. 10,12,14,17,25 High-resolution chemical analysis, performed by using STEM-EDS, showed higher concentrations of dopant cations at the GBs of YSZ and GDC.…”

“…14,15 Such dopant segregation at the GBs can be induced by relaxation of residual stress from size mismatch between the dopant and host cation. 25,[27][28][29][30] Thus, the higher concentration of dopant at the GBs results in a higher population of oxygen vacancies, and the GBs become preferential sites for ORRs. 25,[27][28][29][30] Thus, the higher concentration of dopant at the GBs results in a higher population of oxygen vacancies, and the GBs become preferential sites for ORRs.…”

“…25,[27][28][29][30] Thus, the higher concentration of dopant at the GBs results in a higher population of oxygen vacancies, and the GBs become preferential sites for ORRs. 25,31 Therefore, the higher peak power density and j o value in nanocrystalline interlayers can be ascribed to the higher GB density at the nanocrystalline surfaces, which results in enhanced ORR kinetics. [9][10][11][12] Besides the experimental observations, theoretical calculations also supported the specific role of surface GBs on the 30 In addition to the DFT results, a similar trend was reported via quantum simulation and hybrid Monte Carlo/molecular dynamics.…”

Synthesis and Characteristics of Nano-Ceria Supported Bimetallic Catalysts For S-Tolerant SOFCs

“…Further, cerium and oxygen composition in bare nano-ceria were quantized, with oxygen to cerium ratio in the range of 1.7 to 1.9. The nonstoichiometry of the nano-ceria (CeOx) indicated more oxygen vacancy and higher electronic conductivity than Ce02, which will be benefieial to the reaction bet\veen hydrogen and oxygen ion on the anode side of SOFCs (40)(41)(42)(43). (1) 1689-1696 (2011) A portion of the Cu-ceria specimen was subjected to reduction in a hydrogen atmosphere at 600°C to simulate the practical SOFC operating conditions.…”