Perovskite oxides are promising non-precious metal OER catalysts showing high activity in oxygen evolution in alkaline electrolytes, comparable to that of the state-of-the-art IrO2 catalysts [2], but their stability is in need of improvement. As these oxides exhibit relatively low electronic conductivity carbon, typically acetylene black (AB), is added to enhance their conductivity. However, the thermodynamic potential of carbon oxidation (C + 4OH- → CO2 + 2H2O + 4e-) is 1.03 V vs. RHE at pH 14, much below the OER onset potential. Carbon oxidation causes an increase in the electrode resistance and weakens the carbon-catalyst interaction, eventually limiting the electrolyzer lifespan. Consequently, improving the stability and electronic conductivity of the perovskite-oxide OER catalysts with further enhancement of the OER activity is critical to the application of perovskites as OER catalysts for anion exchnange membrane (AEM) electrolyzer.
In this work, perovskite (La1-xSrx)CoyFe1-yO3-δ (LSCF) was chosen to study the OER activity, stability, and electronic conductivity. In typical ABO3 perovskites, the valance state of cations, i.e., the sum of A and B, should be +6 to balance the overall oxygen valence of -6. The non-stoichiometry caused by the change in the ratio of La/Sr and Co/Fe in the LSCF will affect the OER activity, stability and the electronic conductivity. The effect of this non-stoichiometry of LSCF on the OER performance in alkaline electrochemical cells and AEM electrolyzer, in conjunction with DFT calculations, will be presented in this talk.
Acknowledgements
This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the HydroGEN Consortium.
References
[1] J. Greeley, N. M. Markovic, Energy Environ. Sci., 5 (2012) 9246-9256.
[2] J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough, Y. Shao-Horn, Science, 334 (2011) 1383-1385.