Electrochemically Active Area of Composite BaGd0.3La0.7Co2O6−δ/BaZr0.8Yb0.2O3−δ Oxygen Electrodes by Operando Micro X-ray Absorption Spectroscopy

The electrochemically active area of a patterned BaGd0.3La0.7Co2O6−δ/BaZr0.8Yb0.2O3−δ composite electrode in a proton ceramic electrochemical cell prepared by photolithography and pulsed laser deposition (PLD) was investigated by operando micro X-ray absorption spectroscopy (XAS). X-ray absorption at the Co K-edge was measured under applied cathodic bias and open-circuit conditions at 400–600 °C in 0.01–1 bar O2, and the extension of the electrochemically active area was probed along a line scan parallel to the triple-phase boundary at similar electrode overpotentials. The electrochemically active area was found to increase significantly with decreasing oxygen partial pressure at 500 °C, extending approximately 20 μm along the line scan at 1 bar O2 and approximately 75 μm at 0.01 bar O2, predominantly attributed to a decrease in the oxygen exchange rate. In contrast, the electrochemically active area remained similar in the temperature range 400–600 °C at 1 bar O2, indicating a relatively constant ratio between the oxygen diffusion coefficient and the oxygen exchange rate over this temperature interval.