Electrocatalytic Activities of La0.6Ca0.4CoO3 and La0.6Ca0.4CoO3-Carbon Composites Toward the Oxygen Reduction Reaction in Concentrated Alkaline Electrolytes

Abstract

Perovskites exhibit high activities toward oxygen reduction reaction (ORR) in alkaline media, which are the promising candidates for air-cathode in zinc-air rechargeable batteries. Among them, La 0.6 Ca 0.4 CoO 3 -C was reported with high ORR activities in alkaline solutions. However, the functioning of carbon support towards ORR was rare studied. In this study, La 0.6 Ca 0.4 CoO 3 powder was prepared and characterized by X-ray diffraction, high-resolution transmission electron microscopy, and the Brunauer Emmett Teller gas adsorption technique. The electrocatalytic properties of La 0.6 Ca 0.4 CoO 3 (LCCO) and La 0.6 Ca 0.4 CoO 3 -carbon composite (LCCO-C) layers towards the ORR were comparatively studied using the rotating ring-disk electrode technique in 1, 4, and 6 M KOH electrolytes to reveal the functioning of carbon. The Koutecky-Levich theory and Tafel slope analysis were applied to acquire the overall electron transfer number and kinetic parameters, such as kinetic currents, rate constants, and exchange current densities. The overall electron transfer number was measured to be almost 4 for both LCCO and LCCO-C. A synergetic effect toward the ORR was observed when carbon was present in the LCCO layer, explained by an assumed 2þ2-electron transfer pathway. The ORR activities and kinetics of LCCO-C were better than LCCO, and the synergetic effect (2 þ 2-electron transfer pathway) is proposed as one possible reason.

Micro Emulsion Synthesis of LaCoO3Nanoparticles and their Electrochemical Catalytic Activity

“…This suggested a synergy between LaCoO 3 and carbon. These synergistic effects are consistent with those reported in the literatures [25,28]. The ORR catalytic activity of LaCoO 3 (LCO-SP) samples which was synthesized by using sol-gel process is also observed by applying RDE measurement following the same recipe as described earlier for LaCoO 3 (LCO-ME)-Super P modified GC electrode to compare the different particle effect on the oxygen reduction activity of LaCoO 3 oxide material.…”

“…Both LaCoO 3 and the LaCoO 3 -Super P mixture showed certain activity during O 2 reduction in alkaline solution, but the oxygen reduction peak of the latter was more positive. This was probably due to carbon participating in the catalysis of reduction in the latter case [25]. Fig.…”

“…A changing trend, similar to that observed in the CV curves, was also observed in the RDE curves, i.e., a relatively high ORR current appeared over the LCOSuper P mixture. Evidently, using LaCoO 3 without carbon led to a comparatively poor performance relative to even that of carbon Super P; this was probably associated with the nonhomogeneous electron transfer inside the film due to the poor electronic conductivity of perovskite oxides [25]. For comparison, and to clearly display the onset potential, a portion of the graph was magnified and is presented in Fig.…”

“…5a-c). This behavior could be explained by a larger amount of O 2 being adsorbed in the thin film at lower rotation rates, leading to a more noticeable occurrence of an electro reduction current prior to the electro reduction current of O 2 in the bulk electrolyte [25].…”

“…− [24] and series 2e − + 2e − pathways [25] have been proposed for perovskite cathodes. The reactions at the alkaline electrolyte can be written, as shown in Table 1.…”