Enhancement of oxygen evolution reaction activity and durability of Ba0.5Sr0.5Co0.8Fe0.2O3-δ by CO2 thermal treatment

This work demonstrates that in situ formation of carbonate layer on the surface of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) obtained by exposure to CO2 during heating between 500 degrees C and 700 degrees C can provide enhanced oxygen evolution reaction (OER) performance and durability in an alkaline solution relative to the original BSCF. Three temperatures, i.e., 500 degrees C, 600 degrees C, and 700 degrees C were chosen to perform the CO2 thermal treatment, resulting into BSCF-500, BSCF-600, and BSCF-700 samples. The OER was enhanced in the order of BSCF-500 < BSCF-700 < BSCF-600. BSCF-600 showed the best OER performance, i.e., a low overpotential of 0.36 V required to attain 10 mA cm(-2) current density as well as a mass activity of 74.14 Ag-cat(-1) and a specific activity of 5.04 mA cm(cat)(-2) at an overpotential of 0.4 V. The OER performance durability of BSCF-600 was highlighted by its ability to maintain a stable potential of around 1.61 V vs. RHE (RHE: reversible hydrogen electrode) when charged at a constant current density of 10 mA cm(-2) through out the 800 min continuous chronopotentiometry test. The enhanced OER performance for BSCF-600 relative to the original BSCF is attributed to three factors: (i) higher electrochemically active surface area; (ii) faster charge transfer rate and higher electrical conductivity; and (iii) modified oxidation state of cobalt ions. The formation of thin carbonate layer in BSCF-600 appears to suppress the durability issue observed in BSCF. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.