One-pot synthesis of La 0.7 Sr 0.3 MnO 3 supported on flower-like CeO 2 as electrocatalyst for oxygen reduction reaction in aluminum-air batteries (original) (raw)
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ACS Applied Nano Materials, 2018
A nano-architectured La 2 O 2 CO 3-La 0.7 Sr 0.3 MnO 3 hybrid catalyst is prepared by a facile hydrothermal method. The La 2 O 2 CO 3 nano-rods are well distributed on the regular hexagonal La 0.7 Sr 0.3 MnO 3 nano-sheet. The La 2 O 2 CO 3-La 0.7 Sr 0.3 MnO 3 catalyst has better catalytic activity to oxygen reduction reaction than that of La 2 O 2 CO 3 or La 0.7 Sr 0.3 MnO 3. The reaction kinetics result shows that La 2 O 2 CO 3-La 0.7 Sr 0.3 MnO 3 sample follows a four-electron transferred process during oxygen reduction reaction. Furthermore, the stability of La 2 O 2 CO 3-La 0.7 Sr 0.3 MnO 3 is higher than that of Pt/C. By using La 2 O 2 CO 3-La 0.7 Sr 0.3 MnO 3 as the cathode catalysts for aluminum-air battery, the power densities can reach 223.8 mW cm −2. The high catalytic performance of the La 2 O 2 CO 3-La 0.7 Sr 0.3 MnO 3 can be attributed to the strong interaction between the La 2 O 2 CO 3 material and La 0.7 Sr 0.3 MnO 3 material.
Solid State Ionics, 2018
CeO 2 coatings (1.0, 3.5 and 5.0 mass%) have been obtained at the surface of 150-200 nm Li [Li 0.13 Ni 0.2 Mn 0.47 Co 0.2 ]O 2 (LLNMC) particles. According to TEM and STEM-EDX data, at 1% CeO 2 , the coating consists of 20-60 nm spherical ceria particles, while at 5%, their size is increased to 150-200 nm. The reversible electrochemical capacity of the coated samples is larger than for bare LLNMC, especially at higher discharge rates. The maximum capacity is observed for the 1% CeO 2-coated sample (235 mAh g −1 at U = 2.0-4.8 V). It is essential that the extra capacity of CeO 2-coated samples is appeared since the first cycles and, hence, could not be attributed to the protection of LLNMC from the electrochemical degradation by CeO 2. The cyclic voltammetry curves of the 1% coated sample demonstrate a considerable effect at U = 4.2-4.6 V that could be associated with redox processes in the oxygen sublattice of LLNMC. Taking into account a significant activation of the oxygen species at the surface of ceria nanoparticles, the observed capacity increase of LLNMC could be affiliated with the catalytic effect of CeO 2 on the oxidation of lattice oxygen in LLNMC rather than the protecting effect of ceria particles.
Applied Materials Today, 2020
Although transition metal oxides are important potential catalytic cathode materials for Li-O 2 batteries (LOBs), their poor cycle durability at high current density, high overpotentials and side reaction are still the challenges to solve. Herein, CeO 2 /Co 3 O 4 nanowire arrays grown on Ni foam were fabricated as a free standing cathode of LOBs, featuring a controllable discharge/charge products evolution route. CeO 2 served as active sites for nucleation, initial growth and decomposition of Li 2 O 2. The embedded CeO 2 nanocrystalline on Co 3 O 4 substrate dominated the initial discharge/charge product evolution with multi-formation kinetics of crystal Li 2 O 2 and Li 2-x O 2 at high current densities which leading to low overpotentials and efficient decomposition of discharge products. Owing to the stable structure, the CeO 2 /Co 3 O 4 nanowires were found to energetically favor the mass transport between the electrode/electrolyte interface during long cycle testing. As a consequence, excellent cyclability of 500 cycles at high current density (500 mA g −1) under a fixed capacity of 500 mA h g −1 with low overpotentials of 0.2 V and 1.0 V for discharge/charge process (after 500 cycles) were achieved. The present work provides a new strategy and intrinsic insight in designing high-performance metal oxides electrocatalysts with a fine-tuned structure for LOBs.
In Situ Formed Layered-Layered Metal Oxide as Bifunctional Catalyst for Li-Air Batteries
The electrochemical activity of a Li-air battery cathode catalyst derived from the lithium rich layered-layered metal oxide of the formula 0.5Li 2 MnO 3 .0.5LiMn 0.5 Ni 0.35 Co 0.15 O 2 is reported. The catalyst formed in-situ by electrochemically de-lithiating this metal oxide embedded in a high surface area carbon matrix behaved as a bifunctional catalyst for O 2 reduction reaction (ORR) and O 2 evolution reaction (OER) in a non-aqueous Li-O 2 cell. Cyclic voltammetry (CV) in both half and full cells revealed enhanced OER and ORR catalytic activity by: i-) displaying a more positive potential shift during ORR, ii-) stabilizing the initial ORR product LiO 2 , and iii-) showing an additional potential step in the oxidation of the ORR products. In the CV of catalyzed cells, a reduction peak appeared before the main peroxide (O 2 2−) formation peak suggesting that the catalyst stabilizes the superoxide (O 2 −) formed prior to the formation of peroxide. Evidence for LiO 2 as the initial discharge product was obtained from both the Raman spectrum and X-ray diffraction (XRD) pattern of Li-air cell cathodes after galvanostatic discharge to 2 V. Surface features for the discharged cathodes obtained from Field Emission Scanning Electron Microscope (FESEM) unveiled dissimilar morphologies for the discharge products from catalyzed and uncatalyzed cells, originating from different nucleation mechanisms. The catalyzed cells exhibited longer cycle life than uncatalyzed cells under similar cycling conditions. Conventional lithium ion batteries with one-electron reversible transfer per metal in transition metal oxide cathodes are not capable of a 300-mile (500 km) driving range for all-electric vehicles on a single charge. Advanced batteries having at least 50 percent higher energy density than today's best Li-ion battery are needed to realize such electric vehicles. In order to overcome the constraints imposed on the reversible capacity of cathode materials by the lithium intercalation reaction, it is increasingly becoming necessary to change the electrode reaction process to one of atom displacement reaction involving multiple electron transfer per atom. In this connection recharge-able non-aqueous lithium-air (i.e. Li/O 2) batteries 1,2 have opened up new horizons to search for higher energy density batteries that could achieve the 300-mile EV driving range. Now there is consensus that the ORR mechanism in non-aqueous electrolytes is different from that observed in aqueous electrolytes relevant to H 2 /O 2 fuel cells. Generally O 2 reduction reactions (ORR) in non-aqueous electrolytes, including organic electrolytes and room temperature ionic liquids, occur in the following steps: 3–6 Step 1: O 2 + Li + + e − → LiO 2 (initial one-electron electrochem-ical reduction step which can rarely be observed) Step 2: 2LiO 2 → Li 2 O 2 + O 2 (chemical decomposition to the common discharge product) Step 3: LiO 2 + e − + Li + → Li 2 O 2 (electrochemical reduction of initial reduction product LiO 2 to the common discharge product) Step 4: Li 2 O 2 + 2e − + 2Li + → 2Li 2 O (electrochemical reduction product at low potentials possible in a potentiodynamic experiment) The oxygen evolution reaction (OER) paths do not necessarily follow the reverse of those in the ORR. The most probable OER reactions are: Step 5: LiO 2 → O 2 + Li + + e − Step 6: Li 2 O 2 → O 2 + 2Li + + 2e − Step 7: Li 2 O → 1/2O 2 + 2Li + + 2e − The LiO 2 formed in step 1 is very short-lived in most non-aqueous electrolytes due to the moderately soft basicity of O 2 − which discourages its association with the hard Lewis acid Li +. The superoxide specie in most cases decomposes readily to peroxide (O 2 2−) (step 2) which is a hard base and it readily combines with Li + to form Li 2 O 2. In high donor number (DN) electrolytes such as dimethyl sulfoxide (DMSO, DN = 29.8), the acidity of Li + ions in solution is substantially decreased by its solvation with DMSO such that (DMSO) n Li + acts as a soft acid which enables the superoxide species to become ion-paired with Li + in DMSO. In such cases, the (DMSO) n LiO 2 has a relatively longer lifetime in solution. Throughout this work, we used tetra ethylene glycol dimethyl ether (TEGDME) based electrolytes which has a low Gutmann DN (DN = 16.6) providing short life time for the superoxide initially formed in the reduction of O 2. As a result the superoxide quickly decomposes according to the reaction in step 2 in this electrolyte. The discharge product of an uncatalyzed Li-O 2 cell utilizing TEGDME/LiX where X − is CF 3 SO 3 − or PF 6 − is Li 2 O 2. 5 Several technical issues and possible solutions pertaining to the Li air batteries have been documented. 3,7–10 Among them, appropriate cathode catalysts 11–13 to enhance the ORR and OER kinet-ics and reversibility is well recognized. In this paper we show that i-) the layered-layered metal oxide of the approximate composition 0.5MnO 2 .Mn 0.5 Ni 0.35 Co 0.15 O 2 obtained by the electrochemical delithiation of 0.5Li 2 MnO 3 .0.5LiMn 0.5 Ni 0.35 Co 0.15 O 2 promotes the stabilization of the initial ORR product LiO 2 by the catalyst which in turn lowers the voltage polarization of the oxidation reaction during Li-O 2 cell charging and ii-) the stabilization of the initial ORR product LiO 2 by the catalyst also lowers the activation energy of oxygen reduction reaction (Li-O 2 cell discharge) which improves the power density of the battery. Experimental Chemical reagents.—Anhydrous grade ≥99.8% acetonitrile (CH 3 CN), purum grade ≥98.0% tetraethylene glycol dimethyl ether (TEGDME), anhydrous grade ≥99.5% 1,2-dimethoxyethane (DME), and electrochemical grade tetrabutylammonium hexafluorophosphate (TBAPF 6) were purchased from SigmaAldrich, Allentown, PA. Purolyte lithium hexafluorophosphate (LiPF 6) certified to contain less than 20.0 ppm water was purchased from Novolyte Technologies and used without further treatment. Metals basis 99.9% Li foil purchased from Alfa Aesar Company was used as anode of the Li-O 2 cells. Soon after their arrival, all these reagents were stored in an MBraun Lab-master 130 argon-filled glove box with moisture maintained below 5 ppm. Synthesis of the catalyst (0.5Li 2 MnO 3 .0.5LiMn 0.5 Ni 0.35 Co 0.15 O 2).—In a synthesis, appropriate amounts of Mn(Ac) 2 .4H 2 O (Sigma Aldrich >99%), Ni(NO 3) 2 .6H 2 O (Alfa Aesar-Puratronic)
Batteries & Supercaps, 2018
Active and stable bifunctional electrocatalysts are required for large-scale deployment of rechargeable metal-air and metal-O2 batteries. This is hindered by the large overpotentials of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in alkaline media, where peroxide is an undesired side product. We study the suitability of epitaxial (001)-oriented La0.6Sr0.4MnO3 perovskite surfaces as a bifunctional catalyst using a rotating-ring disk electrode (RRDE) assembly and focus particularly on the selectivity of the ORR. The peroxide yield is above 50% during ORR-only investigations in the scan range of 0.69 to 0.99 V vs. RHE where the CV traces are reproducible. In contrast, the peroxide yield is drastically reduced during OER-ORR cycling where a peroxide yield below 10% is reached during the ORR in the scan range of 0.74 V to 1.74 V vs. RHE. Our study highlights the importance of the electrode history and thus clearly demonstrates that separate studies of the OER and ORR are insufficient to optimize bifunctional electrocatalysts.
Revealing the Li2O2 Nucleation Mechanisms on CeO2 Catalysts for Lithium‐Oxygen Batteries
ChemCatChem, 2020
The addition of ceria (CeO2) nanoparticles to the cathode of a lithium‐oxygen battery results in increased capacity, lower overpotentials and better cyclability. To shed light on the mechanisms of this performance enhancement, we have investigated the early stages of Li2O2 nucleation at stoichiometric and reduced ceria surfaces by means of atomistic simulations based on density functional theory. Adsorption energies are stronger on ceria than on graphene, that is, nucleation mainly would take place on the oxide. The adsorption process of O2 is the one that determines the nucleation sites for the Li2O2 formation on the different CeO2 surfaces. The LiO2 intermediate is adsorbed at the O2 reduction sites. On the reduced (100) surface, the LiO2 tends to adsorb dissociatively, opening up the possibility to the formation of other species than the desired end‐product, Li2O2. On the contrary, optimal properties are found for the reduced (110) surface, which should therefore be the most acti...
ACS applied energy materials, 2020
Developing inexpensive, noble metal-free, efficient, stable and bifunctional electrocatalyst has attracted significant research interest in electrocatalysis and air battery based energy storage devices. The fluorinated copper manganese oxide (FCMO) is synthesized in aqueous medium by simple way using hot plate and fume hood. The FCMO catalyst is relatively inexpensive than Pt, Ru and Ir based catalyst, less hazardous than Co based catalyst and at the same time comparable with Fe-Ni based catalyst that only have stable performance in basic medium The FCMO is utilized in combination with carbon black as FCMO-carbon black by dispersing FCMO over carbon black to improve the electron transport efficiency. The FCMO catalyst and FCMO-carbon black show ORR and OER in both the acidic as well as basic medium an impressive property of larger pH window stability with performance. The ORR was found to be a two electron process on both catalytic systems in both acidic and alkaline media. The FCMO-carbon black showed ORR (0.43 V) and OER (1.51 V) vs RHE in 0.5M H 2 SO 4. The onset potential of FCMO-carbon black was found an impressive 0.94 V vs. RHE for ORR and relatively competitive OER at 1.54 V vs. RHE in 0.1 M KOH. The FCMO-carbon black catalyst was also deposited on conducting carbon cloth and used as an air-cathode in hybrid
Journal of Materials Chemistry, 2012
Sr 0.95 Ce 0.05 CoO 3Àd (SCCO) particles loaded with copper nanoparticles on their surface are shown to be excellent, low-cost, and stable bifunctional catalysts for the oxygen-reduction and oxygen-evolution reactions (ORR and OER) in aqueous solution. Evidence for the presence of Ce 3+ and Co 2+ as well as Co 4+ and Co 3+ ions revealed by XPS measurements as well as XRD analysis indicates that a CeCoO 2.5 brownmillerite phase may be extruded to the surface. A surface Co 4+ /Co 3+ couple is known to be a good OER catalyst. The performance of the SCCO-based catalysts is better at higher current rates (>0.1 mA cm À2 ) than that of Vulcan XC-72 and even close to that of the 50% Pt/carbon-black catalyst. This catalyst could be used in a metal/air battery or a PEM fuel cell as an efficient and stable bifunctional catalyst.
Ionics, 2019
The kinetics and mechanism of oxygen reduction reaction (ORR) in alkaline medium are studied on lanthanum nickelate materials La 2−x−y Nd x Pr y NiO 4±δ (x = 0, 0.3 and 0.5; y = 0 and 0.2) using the electrochemical technique of the rotating disk electrode in a 0.5-M solution of NaOH. The oxide powders are synthesized by the citrate-nitrate method. Structural and surface characterizations are performed by X-ray diffraction (XRD) and X-ray photoelectron spectrometry (XPS), while the morphology is studied by scanning electron microscopy (SEM). Electrochemical studies are carried out by linear voltamperometry, cyclic voltamperometry, and impedance spectroscopy. The doped and undoped electrocatalyst composites (La 2−x−y Nd x Pr y NiO 4±δ /C), made of the rare earth nickel oxides mixed with carbon black (Vulcan XC-72(C)), are deposited as a thin layer on a glassy carbon substrate. At room temperature, the undoped electrocatalyst La 2 NiO 4±δ material shows single-step kinetics unlike the doped materials. The doping by the rare earths Nd or/and Pr significantly enhances the electrical conductivity of the electrode under air and the diffusion of oxygen. On the other hand, the steric hindrance between the atomic oxygen orbital (π-orbital (O 2)-π-orbital (O 2)) and the dz 2-orbital (Ni)-π-orbital (O 2) influences the training model of the liaison (dz 2 (Ni)-π (O 2)). The structure, oxygen adsorption, and oxidation states of the catalyst elements have a large influence on the mechanism and kinetics of the ORR. The LNNO3/C and LNPNO5/C electrocatalysts have better electrocatalytic performances, which allow them to be used as a bifunctional electrocatalyst for the reduction of oxygen in alkaline media.