Probing bias-dependent electrochemical gas-solid reactions in (La _xSr_1-x)CoO_3-δ cathode materials

Spatial variability of bias-dependent electrochemical processes on a (La_0.5Sr_0.5)₂CoO_4±δ modified (La_xSr_1-x)CoO_3-δ surface is studied using first-order reversal curve method in electrochemical strain microscopy (ESM). The oxygen reduction/evolution reaction (ORR/OER) is activated at voltages as low as 3-4 V with respect to bottom electrode. The degree of bias-induced transformation as quantified by ESM hysteresis loop area increases with applied bias. The variability of electrochemical activity is explored using correlation analysis and the ORR/OER is shown to be activated in grains at relatively low biases, but the final reaction rate is relatively small. At the same time, at grain boundaries, the onset of reaction process corresponds to larger voltages, but limiting reactivity is much higher. The reaction mechanism in ESM of mixed electronic-ionic conductor is further analyzed. These studies both establish the framework for probing bias-dependent electrochemical processes in solids and demonstrate rich spectrum of electrochemical transformations underpinning catalytic activity in cobaltites. Spatial variability of bias-dependent electrochemical processes on a (La _0.5Sr_0.5)₂CoO_4±δ modified (La_xSr_1-x)CoO_3-δ surface is studied using first-order reversal curve method in electrochemical strain microscopy. Reversible oxygen reduction/evolution reaction (ORR/OER) is activated at voltages as low as 3-4 V. The degree of bias-induced transformation increases with applied bias. ORR/OER is shown to be activated in grains at relatively low biases and larger voltages at grain boundaries.