3DOM Cerium Doped LaCoO₃Bifunctional Electrocatalysts for the Oxygen Evolution and Reduction Reactions

Abstract

A bifunctional oxygen evolution reaction and oxygen reduction reaction (OER/ORR) electrocatalyst, macroporous cerium-doped LaCoO 3 , 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 LaCoO 3 . The catalytic activity of 3DOM La 0.95 Ce 0.05 CoO 3 (3DOM LCCO-0.05) is significantly improved over that of the unmodified LaCoO 3 , with the OER overpotential to reach 10 mA cm À 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.

Strategic Design and Insights into Lanthanum and Strontium Perovskite Oxides for Oxygen Reduction and Oxygen Evolution Reactions

“…It is noted that the change in Co(III) to high spin, oxygen vacancies, and the presence of surface oxygen species are seen to improve bifunctional performance. [ 149 ] In Figure 7j, via a hydrothermal method, potassium was substituted into LaMnO 3 , forming LKMO. The doping of potassium into LCM enhances A site ionic radii, and interaction between manganese ions is exchanged.…”