Improved Redox Cycling Durability in Alternative Ni Alloy-Based SOFC Anodes

Abstract

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.

Redox Durability of Ni-Co Alloy Cermet Anodes for SOFCs

“…The cycling protocol of the redox cycle test conducted to evaluate the redox durability of the anodes is shown in Fig. 3 (11,12). The cycle simulates a system shutdown, which is one of the causes of oxidation in anodes.…”

“…In such anodes, the metallic Ni, which is an excellent catalyst for fuel gas (H2), acts as a catalyst in a reducing atmosphere, while the alloying elements form a dense oxide film on the surface to prevent oxidation of Ni when the atmosphere is switched to an oxidizing atmosphere, and thus high durability against redox is expected. In fact, in a previous study, Ni-alloy anodes with high durability against redox cycling and almost the same performance as conventional anodes under 3% humidified hydrogen fuel were successfully fabricated (11). In this study, we focused on Co among the alloying elements and evaluated the dependence of the electrochemical performance on the concentration of Co in anodes using Ni-Co alloys as electronic conductors and catalysts.…”

Ni-Alloy Fuel Electrodes for Reversible Solid Oxide Cells

“…In these anodes, Co (an alloying element), forms a dense oxide film at the surface, preventing Ni oxidation in oxidizing atmosphere. Thus, Ni-Co alloys display higher durability against redox cycling compared with the Nizirconia cermet (6). In this study, we utilize Ni-Co-GDC and pure Ni-GDC to r-SOCs fuel electrodes and evaluate the effect of Co content on the initial electrochemical performance, and the SOFC/SOEC switching operation durability.…”

In Situ TEM Investigation of Structural Changes in Ni Nanoparticle Catalysts under Gas Atmospheres: Implications for Catalyst Degradation

“…Because Ni catalysts cost less than catalysts based on noble metals, such as platinum, rhodium, and palladium, they are generally employed as electrode catalysts in solid oxide fuel cells (SOFCs) and solid oxide electrolyte cells. However, the surface areas of Ni decrease during redox cycling due to agglomeration, degrading the catalytic activities. , In efforts to improve the redox resistance of Ni catalysts, the influence of their chemical compositions has been investigated. − The catalytic activity of Ni particles also declines during the reformation of gaseous hydrocarbons. This is because carbon deposits form on Ni particle surfaces. , It is known that the deposition of various carbonaceous materials during CO and hydrocarbon decomposition depends on the temperature .…”