Cobalt‐Doped Perovskite‐Type Oxide LaMnO₃ as Bifunctional Oxygen Catalysts for Hybrid Lithium–Oxygen Batteries

Abstract

Perovskite-type oxides based on rare-earth metals containing lanthanum manganate are promising catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline electrolyte. Perovskite-type LaMnO shows excellent ORR performance, but poor OER activity. To improve the OER performance of LaMnO , the element cobalt is doped into perovskite-type LaMnO through a sol-gel method followed by a calcination process. To assess electrocatalytic activities for the ORR and OER, a series of LaMn Co O (x=0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5) perovskite oxides were synthesized. The results indicate that the amount of doped cobalt has a significant effect on the catalytic performance of LaMn Co O . If x=0.3, LaMn Co O not only shows a tolerable electrocatalytic activity for the ORR, but also exhibits a great improvement (>200 mV) on the catalytic activity for the OER; this indicates that the doping of cobalt is an effective approach to improve the OER performance of LaMnO . Furthermore, the results demonstrate that LaMn Co O is a promising cost-effective bifunctional catalyst with high performance in the ORR and OER for application in hybrid Li-O batteries.

Structural and morphological alterations induced by cobalt substitution in LaMnO3 perovskites

“…Porous structures are desirable for electrocatalytic applications because they facilitate the diffusion of electrolyte ions and solvents into the material, thus providing more active catalytic sites. In this context, LaMn1-xCoxO3 perovskites are expected to present an appropriate porosity due to the calcination process employed during the synthesis, which removes both EDTA and citric acid from the structure and promotes the thermal decomposition of nitrate [45]. The surface morphology of a set of LaMn1-xCoxO3 perovskites, with x = 0, 0.2, 0.8 and 1, was examined by SEM microscopy and the results are presented in Fig.…”

“…Besides, the produced Mn 4+ species provides higher oxidation capability than the original Mn 3+ . On the contrary, Liu et al [39] reported that the catalytic activity of the undoped perovskite is higher and, for similar cobalt and manganese content, such catalytic activity decreases drastically due to the alterations induced in the crystal structure by the smaller cation. Nevertheless, they found that the activity toward OER enhances after the introduction of cobalt and reported that LaMn0.7Co0.3O3 perovskite shows the best response toward OER, so this material was suggested as a promising bifunctional electrocatalyst.…”

“…This is due to some combined effects, such as the occurrence of synergy between the two cations, the induction of altered (and more favorable) arrangements in the resulting compound like porous structures that facilitate the diffusion of electrolyte or oxygen into the perovskite material or the formation of additional metal redox pairs [36,37]. Recent studies on LaMn1-xCoxO3 electrocatalysts were carried out by supporting these materials on different carbon structures to enhance their electrocatalytic properties toward ORR and OER [38][39][40][41]. Hu et al [38] and Lee et al [40] observed that little substitution of cobalt for Mn makes the LaMn0.9Co0.1O3 perovskite exhibit a better performance toward ORR with a more positive onset potential and a larger current density than LaMnO3.…”

A bifunctional perovskite oxide catalyst: The triggered oxygen reduction/evolution electrocatalysis by moderated Mn-Ni co-doping

“…Oxygen reduction and evolution reactions (ORR and OER) are cornerstone reactions for electrochemical conversions between chemical and electronic energy [4][5][6]. For example, ORR wieldy exists in fuel cells and the discharge process of metal-air batteries [7,8], while OER is involved in electrolytic water splitting and metal-air batteries during the charge process [9,10]. However, the state-of-the-art noble metal (oxide) electrocatalysts, such as Pt-based materials for ORR and Ir-and Ru-based materials for OER, are significantly limited by the high cost, scarce resource, and low bifunctional activity [11].…”

Oxygen Reduction Reaction Electrocatalysis in Alkaline Electrolyte on Glassy-Carbon-Supported Nanostructured Pr6O11 Thin-Films

“…The ORR activity of the crystalline Pr 6 O 11 sample was better than that of the as-prepared one ( Figure 9A), as clearly revealed when directly superposing the two sets of data on the same axes ( Figure 9B). While the onset potential value (E onset = 0.835 V vs RHE, in the average for such class of materials [46,[75][76][77][78][79][80][81], although in these papers, the materials were tested with carbon as electron-conductive additive) was barely changed compared to the amorphous sample, the limiting current plateaus were better defined. However, they still do not match the expected values for a 4-electron ORR, by a factor ca.…”