Co–O bond covalency change in PrCoO3 by substituting Cu, Mn, and Nb

Abstract

We investigated the effects of various transition metal dopants on the changes in B-site ion-oxygen (B–O) bonding characteristics and the subsequent effects on the electrochemical properties of PrCoO3 (PCMe, PrCo0.9Me0.1O3-δ, Me = Cu, Mn, Nb). The lattice constants of Mn, Cu, and Nb-doped PrCoO3 were increased compared with that of pure PrCoO3 (PCO), and the B–O–B bond angles were determined to be 163.709°, 167.323°, 165.149°, and 161.765° for PCO, PCCu, PCMn, and PCNb, respectively, by Rietveld refinement. The pre-edge peak of the O K-edge shifted to 0.7 eV of lower energy in PCCu as compared with PCO, and to 0.2 eV of lower energy in PCMn. By contrast, PCNb shifted to 0.3 eV of higher energy. Considering the B–O–B bond angle and pre-edge peak shift, the overlap between B 3d and O 2p orbitals can be expected to be the largest in PCCu, indicating the strongest covalency, whereas PCNb has the weakest covalency. The polarization resistance, as an indicator of the ORR activity, was 7.63, 6.67, 8.05, and 9.56 Ω cm2 in PCO, PCCu, PCMn and PCNb, respectively.