Enhanced Bifunctional Catalytic Activity of Manganese Oxide/Perovskite Hierarchical Core-Shell Materials by Adjusting the Interface for Metal-Air Batteries.

LaMnO3 perovskite is one of the most promising catalysts for oxygen reduction reaction (ORR) in metal-air batteries and can be compared to Pt/C. However, the low catalytic activity toward oxygen evolution reaction (OER) limits its practical application in rechargeable metal-air batteries. In this work, the MnO2/La0.7Sr0.3MnO3 hierarchical core-shell composite materials with a special interface structure have been designed via the selective dissolution method. The core of La0.7Sr0.3MnO3 particles is wrapped by the porous and loose MnO2 nanoparticles. The as-prepared MnO2/La0.7Sr0.3MnO3 materials have excellent catalytic activity toward ORR/OER and are used as bifunctional oxygen electrocatalysts for metal-air batteries. Based on results of transmission electron microscopy, X-ray photoelectron spectroscopy, valence-band spectroscopy, and O2 temperature-programmed desorption analysis, we conclude that the bifunctional catalytic activity of the MnO2/La0.7Sr0.3MnO3 materials can be effectively promoted due to the specific interface structure between the La1-xSrxMnO3 core and the MnO2 shell. This can be attributed to three aspects: (a) the electronic conductivity, which is beneficial for providing the faster charge-transfer paths and kinetics at the oxide/solution interface than that of the MnO2 sample; (b) the enhancement of oxygen adsorption capacity due to surface defects (oxygen vacancies) and chemical adsorption, which is helpful to improve the reaction kinetics during the process of oxygen catalysis; and (c) the tuning of oxygen adsorption ability via the moderate Mn-O bond strength, which may be conducive to getting for obtain an enhanced Mn-O bond strength on the surfaces for ORR and a weakened Mn-O bond in the lattice for OER.

One-Pot Synthesis of Co3 O4 /Ag Nanoparticles Supported on N-Doped Graphene as Efficient Bifunctional Oxygen Catalysts for Flexible Rechargeable Zinc-Air Batteries.

Flexible rechargeable zinc-air batteries are considered as one of the most promising power supplies for the emerging flexible and wearable electronic devices. However, the development of flexible zinc-air batteries is stagnant due to the lack of efficient bifunctional catalysts with high oxygen catalytic activity and flexible solid-state electrolytes with high mechanical stability and ionic conductivity. In this work, Co3 O4 /Ag@NrGO composite was synthesized by a facile one-pot method, and the catalyst shows remarkable oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional catalytic activity and good long-term stability. In particular, the OER overpotential of Co3 O4 /Ag@NrGO reaches 437 mV, outperforming that of the commercial IrO2 catalyst. This can be attributed to the combined effects of Co3 O4 , Ag, and N-rGO. Furthermore, PAA (polyacrylic acid) and PVA (polyvinyl alcohol) based gel-electrolytes have been developed as flexible solid-state electrolytes for zinc-air batteries. The results show that PAA-based electrolyte is more favorable to the flexible zinc-air battery with a high power density due to its relatively high ionic conductivity. The maximum power density of flexible zinc-air batteries with Co3 O4 /Ag@NrGO catalyst and PAA-based electrolyte can reach 108 mW cm-2 , which is almost the highest value reached in recent reports. This work will provide valuable guidance for the development of flexible rechargeable zinc-air batteries with high power density and stability.

Electrocatalytic activity of silver decorated ceria microspheres for the oxygen reduction reaction and their application in aluminium-air batteries.

Nanosheet-constructing porous CeO2 microspheres with silver nanoparticles anchored on the surface were developed as a highly efficient oxygen reduction reaction (ORR) catalyst. The aluminum-air batteries applying Ag-CeO2 as the ORR catalyst exhibit a high output power density and low degradation rate of 345 mW cm-2 and 2.6% per 100 h, respectively.

NO oxidation catalysis on copper doped hexagonal phase LaCoO3: a combined experimental and theoretical study.

Cobalt-based perovskite catalysts showed excellent performance towards NO-NO2 oxidation. We systematically investigated the influence of different levels of Cu-doping on the catalytic performance of hexagonal phase LaCoO3 (LaCo1-xCuxO3 (x = 0.1, 0.2, 0.3)) for NO oxidation. The catalytic activities of the oxide catalysts followed the sequence: LaCo0.9Cu0.1O3 > LaCoO3 > LaCo0.8Cu0.2O3 > LaCo0.7Cu0.3O3 where the highest NO conversion for LaCo0.9Cu0.1O3 was 82% at 310 °C. The relevant structural characterizations were conducted by XRD, BET, FTIR and TEM. The interaction between Co and Cu promoted the conversion of NO to NO2. Upon increasing the Cu doping content, a decrease of the performance resulted from the generation of isolated CuO on the surface of the oxides, confirmed using H2-TPR and XPS. Combined with first-principle calculations, we explored the reaction mechanism of NO oxidation on the surface and found that Cu doping would facilitate the reaction by decreasing the energy of oxygen vacancy formation and the NO2 desorption barrier from Co- or Cu-nitrite.