E. Vila

Bio: E. Vila is an academic researcher from Spanish National Research Council. The author has contributed to research in topics: Ceramic & Perovskite (structure). The author has an hindex of 16, co-authored 39 publications receiving 879 citations. Previous affiliations of E. Vila include Centre national de la recherche scientifique.

Preparation and characterization of spinel-type Mn–Ni–Co–O negative temperature coefficient ceramic thermistors

Abstract: Powders of ternary Mn–Ni–Co oxide negative temperature coefficient thermistors were synthesized by a low-temperature alternative route. The procedure allowed straightforward preparation without the addition of any binder, of highly densified Mn–Ni–Co–O semiconducting ceramics as cubic single-phase spinels, at relatively moderate temperature (≈1000 °C). A tentative cation distribution for the Mn1.5Ni0.6Co0.9O4 spinel oxide has been proposed, and its variation with temperature has also been considered. The dilatometric and X-ray powder diffraction studies carried out for Mn1.5Ni0.6Co0.9O4 showed that sintering takes place in a single stage between 900 and 1000 °C, and yields highly densified ceramic with an apparant density larger than 96% of the calculated X-ray density. Scanning electron microscopy showed different microstructures for the Mn1.5Ni0.6Co0.9O4 spinel oxide, depending on sintering conditions. The value of the sensitivity index, β=3068 K, indicates a good technological thermistor performance for this material. © 1998 Chapman & Hall

Structural and Thermal Properties of the Tetragonal Cobalt Manganese Spinels MnxCo3-xO4 (1.4 < x < 2.0)

Abstract: Phase transitions experienced by MnxCo3-xO4 (1.4 700 °C, with a distortion parameter ranging from 1.0263(1) for x = 1.45 to 1.1353(1) for x = 1.9. The existence at T > 725 °C of a nonisolable cubic spinel single phase (space group Fd3m) in the whole compositional range has been shown by high-temperature X-ray diffraction techniques. It readily transforms on quenching into the new tetragonal single phase. When the cubic high-temperature single phase is allowed to cool slowly, it decomposes into a mixture of tetragonal (x ≈ 2) and cubic (x ≈ 1.3) spinel-type phases. The composition x = 1.4 is found to be the upper compositional limit of existence of the cubic Fd3m spinel, when it is synthesized by a low-temperature procedure.

Covalent hybrid of spinel manganese-cobalt oxide and graphene as advanced oxygen reduction electrocatalysts.

Abstract: Through direct nanoparticle nucleation and growth on nitrogen doped, reduced graphene oxide sheets and cation substitution of spinel Co3O4 nanoparticles, a manganese–cobalt spinel MnCo2O4/graphene hybrid was developed as a highly efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline conditions Electrochemical and X-ray near-edge structure (XANES) investigations revealed that the nucleation and growth method for forming inorganic–nanocarbon hybrids results in covalent coupling between spinel oxide nanoparticles and N-doped reduced graphene oxide (N-rmGO) sheets Carbon K-edge and nitrogen K-edge XANES showed strongly perturbed C–O and C–N bonding in the N-rmGO sheet, suggesting the formation of C–O–metal and C–N–metal bonds between N-doped graphene oxide and spinel oxide nanoparticles Co L-edge and Mn L-edge XANES suggested substitution of Co3+ sites by Mn3+, which increased the activity of the catalytic sites in the hybrid materials, further boosting the ORR activity compared with th

Rapid room-temperature synthesis of nanocrystalline spinels as oxygen reduction and evolution electrocatalysts

Abstract: Spinels can serve as alternative low-cost bifunctional electrocatalysts for oxygen reduction/evolution reactions (ORR/OER), which are the key barriers in various electrochemical devices such as metal-air batteries, fuel cells and electrolysers. However, conventional ceramic synthesis of crystalline spinels requires an elevated temperature, complicated procedures and prolonged heating time, and the resulting product exhibits limited electrocatalytic performance. It has been challenging to develop energy-saving, facile and rapid synthetic methodologies for highly active spinels. In this Article, we report the synthesis of nanocrystalline M(x)Mn(3-x)O(4) (M = divalent metals) spinels under ambient conditions and their electrocatalytic application. We show rapid and selective formation of tetragonal or cubic M(x)Mn(3-x)O(4) from the reduction of amorphous MnO(2) in aqueous M(2+) solution. The prepared Co(x)Mn(3-x)O(4) nanoparticles manifest considerable catalytic activity towards the ORR/OER as a result of their high surface areas and abundant defects. The newly discovered phase-dependent electrocatalytic ORR/OER characteristics of Co-Mn-O spinels are also interpreted by experiment and first-principle theoretical studies.

Covalent Hybrid of Spinel Manganese-Cobalt Oxide and Gra-phene as Advanced Oxygen Reduction Electrocatalysts

Abstract: Through direct nanoparticle nucleation and growth on nitrogen doped, reduced graphene oxide sheets and cation substitution of spinel Co3O4 nanoparticles, a manganese-cobalt spinel MnCo2O4/graphene hybrid was developed as a highly efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline conditions. Electrochemical and X-ray near edge structure (XANES) investigations revealed that the nucleation and growth method for forming inorganic-nanocarbon hybrid results in covalent coupling between spinel oxide nanoparticles and N-doped reduced graphene oxide (N-rmGO) sheets. Carbon K-edge and nitrogen K-edge XANES showed strongly perturbed C-O and C-N bonding in the N-rmGO sheet, suggesting the formation of C-O-metal and C-N-metal bonds between N-doped graphene oxide and spinel oxide nanoparticles. Co L-edge and Mn L-edge XANES suggested substitu-tion of Co3+ sites by Mn3+, which increased the activity of the catalytic sites in the hybrid materials, further boosting the ORR activity compared to the pure cobalt oxide hybrid. The covalently bonded hybrid afforded much greater activity and durability than the physi-cal mixture of nanoparticles and carbon materials including N-rmGO. At the same mass loading, the MnCo2O4/N-graphene hybrid can outperform Pt/C in ORR current density at medium overpotentials with superior stability to Pt/C in alkaline solutions.

Oxygen Reduction in Alkaline Media: From Mechanisms to Recent Advances of Catalysts

Abstract: The oxygen reduction reaction (ORR) is an important electrode reaction for energy storage and conversion devices based on oxygen electrocatalysis. This paper introduces the thermodynamics, reaction kinetics, reaction mechanisms, and reaction pathways of ORR in aqueous alkaline media. Recent advances of the catalysts for ORR were extensively reviewed, including precious metals, nonmetal-doped carbon, carbon–transition metal hybrids, transition metal oxides with spinel and perovskite structures, and so forth. The applications of those ORR catalysts to zinc–air batteries and alkaline fuel cells were briefly introduced. A concluding remark summarizes the current status of the reaction pathways, advanced catalysts, and the future challenges of the research and development of ORR.