Nanoscale Probing of Voltage Activated Oxygen Reduction/Evolution Reactions in Nanopatterned (La xSr1- x)CoO3- δ Cathodes.

Bias-dependent mechanisms of reversible and irreversible electrochemical processes on a (La_0.5Sr_0.5)₂CoO_4±δ modified (La_xSr_1-x)CoO₃- surface are studied using dynamic electrochemical strain microscopy (D-ESM). The reversible oxygen reduction/evolution process is activated at voltages as low as 3-4 V and the degree of transformation increases linearly with applied bias. The irreversible processes associated with static surface deformation become apparent above 10-12 V. Post-mortem focused-ion milling combined with atomic resolution scanning transmission electron microscopy and electron energy loss spectroscopy is used to establish the mechanisms of irreversible transformations and attribute it to amorphization of the top layer of material. These studies both establish the framework for probing irreversible electrochemical processes in solids and illustrate rich spectrum of electrochemical transformations underpinning electrocatalytic activity in cobaltites. [ABSTRACT FROM AUTHOR]