Catalytic Activity of Ceria-Based Complex Metal Oxides in Alkaline and Acidic Environments
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Catalytic Activity of Ceria-Based Complex Metal Oxides in Alkaline and Acidic Environments Matthew C Schrandt1, Praveen Kolla1, A. Smirnova2 1 Materials Engineering and Science Program, South Dakota School of Mines and Technology, Rapid City, SD 57701, U.S.A. 2 Department of Chemistry and Biological Science, South Dakota School of Mines and Technology, Rapid City, SD 57701, U.S.A. ABSTRACT Pt catalysts are the leading catalysts for use in ORR. However, Pt is an expensive catalyst and with limited supply can not be considered a sustainable material for feasible application that is scalable in the economy. This calls for new solutions for catalyst materials that either mitigate the amount of Pt used in catalysts by developing hybrid catalysts, or to replace Pt altogether with a material with similar or better catalytic activity. Perovskite LSCF and Fluorite GDC materials with proven catalytic activity in solid oxide fuel cells are herein explored for their catalytic reduction of oxygen for use at low temperatures. Since the materials lack electronic conductivity at low temperatures, we have improved their conductivity with graphene. The resulting materials are compared to Pt in their ORR catalytic capabilities and electronic conductivity. INTRODUCTION Although the oxygen reduction reaction (ORR) is important in a variety of electrochemical processes and technologies such as sensors and metal-air batteries, the application of the ORR in fuel cells is of particular interest. The ORR slow kinetics in metal air batteries and PEM fuel cells requires novel approaches for the development of catalytically active nanostructures with a final goal of commercialization. Platinum and platinum alloys are the most efficient ORR catalysts, but they are expensive. [1,2] Current study is focused on ceria based metal oxides and lanthanum based perovskites as ORR catalysts. These materials have been extensively studied as catalysts (perovskites) or promoters (gadolinia doped ceria oxide) in high temperature catalysis and solid oxide fuel cells. [3] EXPERIMENT The synthesis of complex metal oxides, such as Gd0.1Ce0.9O3-δ fluorite and two ABO3 perovskites with different chemical composition and iron-cobalt ratio on B-site (La0.6Sr0.4Co0.8Fe0.2O3-δ and La0.6Sr0.4Co0.6Fe0.4O3-δ) was performed using a modified Pechini method followed by heat-treatment at 900°C and 1200°C in air, respectively. [4] Their crystal structure identification and morphological characterization was performed by XRD and SEM. The electrochemical catalytic activity in acidic and alkaline media was studied with cyclic voltammetry and rotating disc electrode in 3-cell configuration with Ag/AgCl, 0.1M KCl reference electrode. The XRD spectra of the materials sintered at 900°C in air show well defined crystal structure (Figure 1). GDC and LSCF materials were further explored after being mixed with graphene in different ratios. Table I enumerates the composition and labels used for the materials explored.
Table I – Synthesized materials and their labels. Gd0.1Ce0.9O2-δ (GDC
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