3DOM Cerium Doped LaCoO3 Bifunctional Electrocatalysts for the Oxygen Evolution and Reduction Reactions

A bifunctional oxygen evolution reaction and oxygen reduction reaction (OER/ORR) electrocatalyst, macroporous cerium-doped LaCoO3, was designed based on a dual strategy that included (1) constructing a three-dimensionally ordered macroporous (3DOM) structure to increase the electrochemical surface area and (2) varying amount of cerium substitution from 0.02 to 0.15 mole fraction of the A site to alter the intrinsic activity of LaCoO3. The catalytic activity of 3DOM La0.95Ce0.05CoO3 (3DOM LCCO-0.05) is significantly improved over that of the unmodified LaCoO3, with the OER overpotential to reach 10 mA cm(-2) lowered by 190 mV, the ORR limiting current density doubled, and the OER-ORR potential gap reduced by 220 mV to 1.07 V. This enhanced activity is attributed to the increased electrochemical surface area and specific activity, as evidenced by the greater double-layer capacitances and the lower charge transfer resistances determined by electrochemical impedance spectroscopy (EIS). Furthermore, X-ray diffraction (XRD) and X-ray photospectroscopy (XPS) results reveal that these enhanced OER/ORR activities are possibly related to the transformation of the cobalt(III) spin state from low to intermediate or high-spin, and the increasing amount of surface oxygen species and oxygen vacancies.