Catalytic Activity of PrNixCo1-XO3 - Graphene nanocomposites for Sustainable Energy Application

Cobalt-containing perovskites ABO₃ with praseodymium in A-site have been investigated as a possible candidate for cathode material for intermediate temperature solid oxide fuel cells. It was found that the conductivity of these compounds does not change significantly with temperature. At close to room temperatures they have conductivity similar to that at high temperatures (1580 S∙cm⁻¹ at 50°C and 1031 S∙cm⁻¹ at 1000^°C).¹ This could be favorable for the oxygen reduction reaction/oxygen evolution reaction (ORR/HER) catalytic activity while considering energy storage and generating devices, such as fuel cells or metal air batteries.

Pt catalysts are the leading catalysts for use in ORR.² 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.

Praseodymium based pyrochlores (PrNi_xCo_1-xO_3-d) with three concentration of Co ranging from x=0.1, 0.5, and 0.9 have been synthesized using a modified nitrate-glycine Pechini method and sintered at different temperatures, specifically 900°C and 1200^°C. The XRD data shown in figure 1 indicates that the peaks responsible for the PrNi_xCo_1-xO_3-d perovskite structure are present in the materials.¹

The electrochemical performance of the perovskites sintered at 1200^°C and tested in KOH (0.1M) demonstrated that PrNi_0.9Co_0.1O_3-d has the highest ORR activity in comparison to the two other perovskites. This activity gradually increases with an increasing ratio of cobalt to nickel at the B site.

The electrochemical performance for the samples with and without graphene in acidic (HClO₄) and basic (KOH) solutions will be presented and discussed in terms of mass and catalytic activity in comparison to Pt/graphene as a baseline.

Fig. 1: XRD data PrNi_0.5Co_0.5O_3-d after 1200°C sintering. 

Fig. 2: Cyclic voltammetry of PrNi_xCo_1-xO_3-dfor x = 0.1 (solid line), 0.5 (dotted line), 0.9 (dashed line) in an oxygen purged KOH (0.1 M) solution.

REFERENCES:

¹   S. Huang, Q. Lu, S. Feng, G. Li, C. Wang, J. of Power Sources 199,150 (2012).

²   W. Vielstich, H. Okokawa, and H.A. Gasteiger, Handbook of Fuel Cells: Fundamentals, Technology, and Applications, Wiley (2009).