Mean Intrinsic Activity of Single Mn Sites at LaMnO3 Nanoparticles Towards the Oxygen Reduction Reaction (original) (raw)
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International Journal of Innovative Technology and Exploring Engineering, 2020
Current paper, we have examined lanthanum manganese cobalt (LaMn1-xCoxO3) perovskite nanoparticles synthesized by utilizing the sol-gel process and following calcinated at 450 °C for 1h and 900 °C for 7h, respectively. The fabricated alloys show single-phase perovskite structure is an order of LaMn1-xCoxO3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1). The synthesized LaMn1-xCoxO3 perovskite oxide nanoparticles have the crystal structure, and powder morphology properties were investigated by X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM), respectively. The perovskite structure has been shown to be particularly effective for the catalytic reactions of ORR and OER in alkaline medium. The merged valance transition metal oxides are bifunctional electrocatalysts which give rise to potential candidates, the electrochemical functioning of the LaMn1-xCoxO3 catalyst was entirely investigated. All compounds of ORR polarization curves show that the four-electron pathway, whi...
Journal of the American Chemical Society, 2022
The atomistic rationalization of the activity of transition metal oxides toward oxygen electrocatalysis is one of the most complex challenges in the field of electrochemical energy conversion. Transition metal oxides exhibit a wide range of structural and electronic properties, which are acutely dependent on composition and crystal structure. So far, identifying one or several properties of transition metal oxides as descriptors for oxygen electrocatalysis remains elusive. In this work, we performed a detailed experimental and computational study of LaMn x Ni 1−x O 3 perovskite nanostructures, establishing an unprecedented correlation between electrocatalytic activity and orbital composition. The composition and structure of the single-phase rhombohedral oxide nanostructures are characterized by a variety of techniques, including X-ray diffraction, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and electron microscopy. Systematic electrochemical analysis of pseudocapacitive responses in the potential region relevant to oxygen electrocatalysis shows the evolution of Mn and Ni d-orbitals as a function of the perovskite composition. We rationalize these observations on the basis of electronic structure calculations employing DFT with HSE06 hybrid functional. Our analysis clearly shows a linear correlation between the OER kinetics and the integrated density of states (DOS) associated with Ni and Mn 3d states in the energy range relevant to operational conditions. In contrast, the ORR kinetics exhibits a second-order reaction with respect to the electron density in Mn and Ni 3d states. For the first time, our study identifies the relevant DOS dominating both reactions and the importance of understanding orbital occupancy under operational conditions.
Journal of Electroanalytical Chemistry, 2018
Lanthanum based electrocatalytically active LaMO 3 (M=Cr, Mn, Fe, Co, Ni) perovskites were synthesized using a single step solution combustion technique. The structural and morphological properties of the catalysts were studied using XRD, SEM, and TEM. The synthesis conditions are found to have a siginificant effect on the nature of the nanoparticles and it can be tuned to synthesize amorphous or crystalline materials. The perovskites showed exceptional performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline medium. LaMnO 3 is found to be most active for ORR, whereas LaCoO 3 for OER. The onset potential of LaMnO 3 is-0.12 V, and for other La-transition metals is nearly-0.2 V. The Koutechy-Levich
Catalysis Today, 2020
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Electrocatalysis
Lanthanum-based perovskites (LaMnxCo1-xO3 (0 ≤ x ≤ 1)) were synthesized using a solution combustion synthesis technique with variable ratios of Co and Mn to investigate the surface property and electrocatalytic characteristics (stability and activity of catalyst) for methanol oxidation reaction (MOR), oxygen reduction reaction (ORR), and oxygen evolution reaction (OER) under alkaline medium (KOH). The structural, chemical, and morphological characterizations of the synthesized catalyst were performed by XRD, FTIR, SEM, TEM, and XPS techniques as a function of the Mn:Co elemental ratio. The time–temperature profile during the combustion process was also monitored to study the completion of the combustion reaction and to understand its impact on the structure of the perovskites. SEM/EDX and XPS analysis confirmed the formation of the targeted ratio of Mn and Co on the catalyst. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) results revealed that all perovskite samples with...
Electric and catalytic properties of doped LaMnO3
Solid State Ionics, 1993
The electric conductivity and Seebeck coefficient of sodium and strontium doped LaMnO3 were measured as a function of temperature and partial pressure of oxygen. The electrical conductivity measurements ofLa1_~la~4nO3 (x=0.1-0.4) suIBest a semiconductor behaviour from room temperature to 800-900°C. Both the electric conductivity and XRD results indicate a decomposition of the perovskites at sufficiently reduced atmosphere. Thus, l.~o.sNao.aMnO3 decomposes at Po2 ~ 10 -17 aUn and Po~ ~ 10 -13 arm at 800 ° C and 1000 ° C, respectively, whereas Lae~Sro.2MnO3 decomposes at/~o~ ~ 10-13 arm at 1000 ° C. At low partial pressures of oxygen the conductivity exhibits a p~4 dependency for both sodium-and s~rontium-doped I.aMuO3. At hi ah partial pressures of oxygen the conductivity is nearly independent of the variation of Po2. Positive Seebeck coefficients indicate p-type carriers in the perovskite oxides. The mobility of the carriers was calculated at 1000°C and 1 arm 02, assuming a small polaron model. For Lat_xNa~MnO3 (xffi0.1, 0.2) the CH4 conversion and C2-selectivity were measured in a quartz fixed-bed reactor as a function of temperature and partial pressure of oxygen. The results indicate a maximum selectivity to C2I-I4 at 820°C for both catalysts. It was observed that Lao.aNao.2MnO3 showed an increasing C2I-I4 selectivity and a decreasing CI-I4 conversion when the Pcm/Po2 ratio increased.
ACS Catalysis
In situ X-ray absorption and emission spectroscopies (XAS and XES) are used to provide details regarding the role of the accessibility and extent of redox activity of the Mn ions in determining the oxygen reduction activity of LaMnO 3 and CaMnO 3 , with X-ray absorption near-edge structure (XANES) providing the average oxidation state, extended X-ray absorption fine structure (EXAFS) providing the local coordination environment, and XES providing the population ratios of the Mn 2+ , Mn 3+ , and Mn 4+ sites as a function of the applied potential. For LaMnO 3 , XANES and XES show that Mn 3+ is formed, but Mn 4+ ions are retained, which leads to the 4e − reduction between 0.85 and 0.6 V. At more negative potentials, down to 0.2 V, EXAFS confirms an increase in oxygen vacancies as evidenced by changes in the Mn−O coordination distance and number, while XES shows that the Mn 3+ to Mn 4+ ratio increases. For CaMnO 3 , XANES and XES show the formation of both Mn 3+ and Mn 2+ as the potential is made more negative, with little retention of Mn 4+ at 0.2 V. The EXAFS for CaMnO 3 also indicates the formation of oxygen vacancies, but in contrast to LaMnO 3 , this is accompanied by loss of the perovskite structure leading to structural collapse. The results presented have implications in terms of understanding of both the pseudocapacitive response of Mn oxide electrocatalysts and the processes behind degradation of the activity of the materials.
Electrochimica Acta, 2020
Recently, many works have demonstrated that tuning the A-site deficient and excessive stoichiometry can yield the positive effects on the catalytic activity of the ABO 3 perovskite toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Whereas, the universality of the deficient or excessive effects and their resulting improving mechanisms on ABO 3 perovskite are still ambiguous and need to be clarified. In this work, the simplest Mn-based perovskite (LaMnO 3) is selected to elucidate the deficient/excessive effects and improving mechanisms on both ORR and OER. We find that A-site deficient stoichiometry is favor to the catalytic activity and stability of LaMnO 3 toward both ORR and OER, whereas A-site excessive stoichiometry is deleterious to the oxygen catalytic activity and stability of LaMnO 3. The high oxygen catalytic activity of La 0$9 MnO 3 (La90) with A-site deficiency toward ORR and OER can be related to its proper Mn cation valence, large amount of oxygen vacancies, upper shift of dband center and strong adsorption capacity to oxygenated species. The results of this work highlight the A-site deficient Mn-based perovskite as the high efficient and commercially viable bifunctional catalyst for aqueous and solid-state flexible zinc-air battery (ZAB) applications.
LaMnO3 perovskite oxides prepared by different methods for catalytic oxidation of toluene
Applied Catalysis B: Environmental, 2014
Perovskite-type oxides of LaMnO 3 (LMO) were synthesized by citrate sol-gel (SG), glycine combustion (GC) and co-precipitation (CP) methods, respectively. The physicochemical properties of these LaMnO 3 materials were characterized by XRD, N 2 sorption, H 2-TPR and O 2-TPD. Their catalytic performances were evaluated for the oxidation of toluene. It was shown that well-formed perovskite structures were obtained over samples LMO-SG and LMO-GC. Traces of La 2 O 3 phase were detected over sample LMO-CP. The ranking in terms of specific surface area, low-temperature reducibility and concentration of surface adsorbed oxygen species from the highest to the lowest value was LMO-SG > LMO-CP > LMO-GC, which was in good agreement with the catalytic activity order. Sample LMO-SG exhibited the optimum catalytic activity and durability without any deactivation observed during the steady state of 60 h. Its superior catalytic performance could be greatly attributed to its higher specific surface area, better lowtemperature reducibility and more available surface adsorbed oxygen species. The apparent activation energies of samples LMO-SG, LMO-GC and LMO-CP were 71, 84 and 76 kJ mol −1 , respectively. The lowest apparent activation energy of sample LMO-SG was in good agreement with its better catalytic behavior for toluene oxidation.