Electrocatalytic Activity of Non-Stoichiometric Perovskites toward Oxygen Reduction Reaction in Alkaline Electrolytes

Abstract

Perovskite La x Ca 0.4 MnO 3 (x = 0.4, 0.5, 0.6) powder was prepared through a sol-gel method and characterized by X-ray diffraction (XRD), a gas adsorption technique (BET) and transmission electron microscopy (TEM). The electrocatalytic properties of La x Ca 0.4 MnO 3 /C composites towards the oxygen reduction reaction (ORR) were studied using rotating ring-disk electrode (RRDE) techniques and Koutecky-Levich theory in both 1 M and 6 M KOH electrolytes. The results show better ORR activities for non-stoichiometric perovskites than that for stoichiometric La 0.6 Ca 0.4 MnO 3 . The overall electron transfer numbers for these La x Ca 0.4 MnO 3 composites are in the range of 3.2-3.7, and with decreasing values of x the electron transfer number increases and accordingly H 2 O 2 production decreases. These results suggest that the existence of a Mn reduction/oxidation pair in Ca-doped nonstoichiometric perovskites could activate the ORR reaction sites, resulting in improved catalytic activity.

Hollow Co3O4 Nanosphere Embedded in Carbon Arrays for Stable and Flexible Solid‐State Zinc–Air Batteries

“… is the diffusion coefficient of oxygen in the electrolyte, while is the concentration of the dissolved oxygen in the electrolyte at partial pressure of 1 atm. D 0 , C 0 , and v in 1 m KOH is about 1.65 × 10 −5 cm 2 s −1 , 8.3 × 10 −7 mol cm −3 , and 9.5 × 10 −3 cm 2 s −1 , respectively …”

Recent Advances of Lanthanum-Based Perovskite Oxides for Catalysis

“…Partial substituting La (3+) with an alkaline earth element (Ca 2+ or Sr 2+ ) or a lanthanide with a different valence (Ce 4+ ) at the A site introduces oxygen nonstoichiometry into the perovskite structure, leading to an improved oxygen mobility. ,,, Owing to the matched atomic size, strontium (Sr) is commonly doped with La on the A site, forming a La 1– x Sr x MO 3 (M = Fe, Co, Mn) type of structure. − The substitution of La (3 + ) with divalent Sr (2 + ) results in cation vacancies and the formation of high-valence M cations to facilitate oxygen and electron transfer, making this structure a promising candidate for catalyzing ORR in alkaline media . Tulloch et al reported that Sr-dependent ORR performance in 1 M KOH with La 0.4 Sr 0.6 MnO 3 achieved the highest activity among all the La 1– x Sr x MnO 3 compounds (LSMOs) studied .…”

Porous Perovskite La0.6Sr0.4Co0.8Mn0.2O3 Nanofibers Loaded with RuO2 Nanosheets as an Efficient and Durable Bifunctional Catalyst for Rechargeable Li–O2 Batteries

“…Recently, Shao-Horn et al experimentally identified the charge-transfer energy, the relative energies of transition-metal (TM) 3d and O 2p valence electronic states, as a key electronic descriptor that interrelates the bulk electronic structure and surface properties of many perovskite oxides. Sunarso et al and Zhu et al illustrated that LaCoO 3 exhibited better catalytic activity and rechargeable stability as a catalyst for metal–air batteries. , Gyenge et al reported that MnO 2 –LaCoO 3 mixed materials have a synergistic catalytic effect toward the ORR and OER, and the insertion of potassium is beneficial in decreasing the overpotentials. , There are two obvious advantages for A-site partial substitution with low-valence metal ions, leading to increasing oxygen vacancies and the proportion of the B-site transition-metal ions to unstable oxidation states (B 3+ /B 4+ redox couple). , Xu et al prepared porous La 0.75 Sr 0.25 MnO 3 nanotubes with high surface area via an electrospinning technique; they reported that the La 0.75 Sr 0.25 MnO 3 nanotubes can improve long cycling life and lower the overvoltage of lithium–oxygen batteries . Since the B site is commonly considered as the active site, the substitution of the B site with a large amount of other ions with redox couples can enhance oxygen mobility. , Moreover, in comparison to nanoparticle or two-dimensional (2D) platelet morphology, nanofibers with a high aspect ratio and porosity usually show superior performance for the ORR/OER reaction since they can maximize the catalytic sites and facilitate the diffusion of electrons and reactants …”

“…34,35 There are two obvious advantages for A-site partial substitution with low-valence metal ions, leading to increasing oxygen vacancies and the proportion of the B-site transition-metal ions to unstable oxidation states (B 3+ /B 4+ redox couple). 36,37 Xu et al prepared porous La 0.75 Sr 0.25 MnO 3 nanotubes with high surface area via an electrospinning technique; they reported that the La 0.75 Sr 0.25 MnO 3 nanotubes can improve long cycling life and lower the overvoltage of lithium−oxygen batteries. 38 Since the B site is commonly considered as the active site, the substitution of the B site with a large amount of other ions with redox couples can enhance oxygen mobility.…”