Investigation of chemical anchoring of nickel catalyst networks by aluminum titanate additives

Abstract

Electrocatalysts are incorporated into a plethora of technologies and material systems such as catalytic converters, reforming systems, multilayer ceramic capacitors, and solid oxide fuel cells (SOFCs). In SOFCs, nickel is commonly the catalyst of choice due to its chemical stability, high catalytic activity, and lower cost. While traditional SOFCs have a bulk mixture of nickel and yttria stabilized zirconia (YSZ) with at least 33 vol% nickel, solution infiltrated anode SOFCs have several benefits including lower nickel vol% to satisfy percolation, better mechanical strength and CTE matching that can improve redox cycling. Coarsening of the fine nickel metal catalyst with microstructures below 1 micrometer have shown a strong propensity to coarsen from thermal migration at temperatures above 700°C. This migration induced degradation by decreasing particle surface area and nickel network connectivity for electrical conduction. Utilizing metastable oxide additives as a minor dopant in the anode cermet system, novel methods of anchoring the metal phase to porous YSZ ceramic scaffolds have been identified as a means to engineer infiltrated anodes for improved performance. Less than 10 wt% aluminum titanate (ALT-Al 2TiO 5), added to YSZ by mechanical mixing, has shown a stepwise process in the formation of NiAl 2O 4 at 1100°C and ZrTiO 4 at 1205°C for chemically binding the nickel phase to YSZ. XRD, SEM, TEM, and EDS characterization coupled with FIB sample preparation has been utilized to identify the size, morphology, composition and temperature at which the anchoring phases form. Area specific resistance tests of component anodes indicate a decrease in degradation of at least 521%/1000 hr compared to infiltrated specimens without the ALT additive. Electrochemical tests of electrolyte supported cells (ESC) show higher initial performance of cells doped with ALT and at least a 1400%/1000 hr reduction in performance degradation at the same nickel loading content.