Comparison of Pyrochlore and Perovskite Electrodes Towards the Oxygen Evolution in Alkaline Media

The identification of economically feasible and high efficient materials towards the oxygen evolution (OER) and reduction (ORR) reactions in alkaline media will constitute a major advancement in a variety of technologies such as water splitting, elctrowinning, fuel cells and metal-air batteries. OER and ORR have proven to be catalytic dependent electrochemical processes, and thus, the catalytic material at the oxygen electrode plays an important role in the performance of such technologies. Numerous research studies have been carried out on the synthesis of new electrode materials in order to reduce the voltage loss associated with the oxygen reactions.

In the present work, a comparison of OER behavior of a group of pyrochlore materials (A₂B₂O_7-δ), and non-noble transition metal perovskites (ABO₃) will be presented. The pyrochlore and perovskite structures were synthesized by a facile two-step combustion method yielding high purity phases with crystallite size in the vicinity of 20nm. The synthesized compounds include La_1-xCa_xFeO₃, Pb₂Ru₂O₇, and their substitutions, compared to un-supported RuO₂ prepared by thermal decomposition of RuCl₃. The catalysts powders were dispersed on a Nafion containing solution to form a catalyst ink [1]. The samples were tested in alkaline media in a traditional three-electrode system under continuous N₂purging. Among the characteristics that make pyrochlores attractive for oxygen electrodes, is the unusual framework containing high density of oxygen vacancies and their apparent ordering which is believed to aid in the oxygen anion mobility [2]. Perovskite materials are attractive due to the wide range of substituting elements that can be employed to tune their electrocatalytic properties.

All the samples were characterized by XRD for phase analysis, XPS for valency, SEM for surface morphology. The OER electrochemical performance has been investigated by means of steady state current measurements. XRD spectra of selected samples and the OER activity are presented in Figure 1a and 1b, respectively. The effect of dopant concentration on the oxygen evolution activity will be discussed.

 Acknowledgements

This work is supported by the IGERT-NSF fellowship and partially funded by the US Department of Energy/NETL, Oak Ridge Institute for Science and Education (ORISE) fellowship.

References

[1] Malkhandi, S., Yang, B., Manohar, A.K., Manivannan, A., Surya Prakash, G.K., and Narayan, S.R., J. Phys. Chem. Lett. 2012, 3, 967-972.

[2] Hyoung Oh, S., Black, R., Pomerantseva, E., Lee, J-H., and F. Nazar, L. Nat. Chem. 2012, 4, 1004-1010.