SOFC anodes impregnated with noble metal catalyst nanoparticles for high fuel utilization

Redox-stable solid oxide fuel cell (SOFC) anodes are developed in order to improve durability at higher fuel utilization, as a possible alternative to conventional Ni-zirconia cermet anodes. Ce0.9Gd0.1O2 (GDC) is utilized as a mixed ionic and electronic conductor (MIEC), in combination with Sr0.9La0.1TiO3 (LST) as an electronic conductor. The stability of noble metals (Rh, Pt, and Pd) is analyzed via thermochemical calculation of stable phases. Noble metal catalyst nanoparticles are incorporated via co-impregnation with GDC. The electrochemical characteristics of SOFC single cells using these anode materials are investigated in highly-humidified H2 at 800 °C. Their stability at high fuel utilization is analyzed. These co-impregnated anodes with highly dispersed noble metal catalysts on the LST-GDC conducting backbones, achieve high I[sbnd]V performance comparable to conventional Ni-cermet anodes. The co-impregnated anodes also achieve considerably high catalytic mass activity. At higher oxygen partial pressure, where the Ni catalyst can be deactivated by oxidation, these noble catalysts are thermochemically stable in the metallic state, and tolerant against oxidation. This class of alternative catalyst, impregnated with low-loading of noble metals could contribute to stable operation in the downstream region of SOFC systems. A simple cost analysis indicates a tolerance of using noble metals, provided their loading is sufficiently low

Improved redox cycling durability in alternative Ni alloy-based SOFC anodes

Repeated reduction and oxidation of metallic nickel in the anodes of solid oxide fuel cell (SOFC) causes volume changes and agglomeration. This disrupts the electron conducting network, resulting in deterioration of the electrochemical performance. It is therefore desirable to develop more robust anodes with high redox stability. Here, new cermet anodes are developed, based on nickel alloyed with Co, Fe, and/or Cr. The stable phases of these different alloys are calculated for oxidizing and reducing conditions, and their electrochemical characteristics are evaluated. Whilst alloying causes a slight decrease in power generation efficiency, the Ni-alloy based anodes have significantly improved redox cycle durability. Microstructural observation reveals that alloying results in the formation of a dense oxide film on the surface of the catalyst particle (e.g. Co-oxide or a complex Fe-Ni-Cr oxide). These oxide layers help suppress oxidation of the underlying nickel catalyst particles, preventing oxidation-induced volume changes/agglomeration, and thereby preserving the electron conducting pathways. As such, the use of these alternative Ni-alloy based cermets significantly improves the redox stability of SOFC anodes