Miguel A. Oliver-Tolentino

Influence on the Electrocatalytic Water Oxidation of M2+/M3+ Cation Arrangement in NiFe LDH: Experimental and Theoretical DFT Evidences

AbstractThis contribution reports the effect of the iron content and M2+/M3+ ratio cation arrangement-distribution on the oxygen evolution reaction (OER) catalyzed by layered double hydroxides. The electrocatalysts, containing variable contents of Ni and Fe, were successfully prepared through a homogeneous precipitation method. The formation of LDH structure was verified by powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Other properties were determined such as specific surface area, electrical conductivity, and surface basicity. First-principles DFT+U calculations complemented and supported the electrochemical results. According to both the electrochemical and simulation results, the increase of the catalytic activity for the OER on the presence of Fe3+ is closely related with the configuration and distribution of Fe and Ni cations in the brucite layer structure. The effect of iron is indirect, favoring the electron hopping on the Ni sites for certain local configuration. Graphical Abstractᅟ

Materials for aqueous sodium-ion batteries: cation mobility in a zinc hexacyanoferrate electrode

The coordination polymer Zn3Na2[FeII(CN)6]2 has an open porous framework that is stable in acidic and neutral aqueous solutions and appears to be an attractive solid for investigation as a material for sodium ion-based batteries. The easy ion exchange of Na+ by bigger cations (such as K+, Rb+ and Cs+) and the existence of the oxidized species Zn3[FeIII(CN)6]2 (as a stable phase) support the present study of the redox reaction and stability in aqueous media under electrochemical conditions for all the series, including the effect of the accompanying cation on the mobility of sodium in the framework. When a study was carried out in a solution of sodium ions, in the material structure K+ and Rb+ were progressively displaced by the sodium ions, which was ascribed to their higher mobility. However, when an experiment was conducted using a solution containing Cs+ or in an aqueous solution of NaNO3, from Zn3Cs2[FeII(CN)6]2, the mixed composition Zn3NaCs[FeII(CN)6]2 was formed. The results discussed here are supported by the electrochemical and spectroscopic measurements. Galvanostatic experiments on the Zn3Cs2[FeII(CN)6]2 system in a solution of sodium ions revealed a capacity retention of 75% during 40 charge/discharge cycles.

Bifunctional electrocatalysts for oxygen reduction/evolution reactions derived from NiCoFe LDH materials

Materials obtained from thermal treatment of thermally treated NiCoFe-layered double hydroxides (LDH) with different Ni:Co ratios were evaluated as bifunctional catalysts for Oxygen Reduction Evolution and Evolution Reduction Reactions in alkaline media. The structural properties of synthesized materials were characterized by X-ray diffraction, Fourier-transform infrared, Raman, and X-ray photoelectron spectroscopies, whereas the basicity of each material was evaluated by temperature-programmed desorption of carbon dioxide. The results revealed the presence of inverse spinel structure with different compositions and a NiO phase with different amounts in the sample, while the electrochemical results showed a high activity towards oxygen reactions. The sample with higher amount of NiO and the lowest substitution grade on tetrahedral sites in the spinel-type structure exhibited the best catalytic activity.Graphical Abstract