DSpace Comunidad:
http://hdl.handle.net/10045/29831
2024-03-29T09:44:32ZFormic acid oxidation on different coverages of Bismuth-modified Pt(1 0 0): A detailed voltammetric and FTIR study
http://hdl.handle.net/10045/135717
Título: Formic acid oxidation on different coverages of Bismuth-modified Pt(1 0 0): A detailed voltammetric and FTIR study
Autor/es: Wei, Zhen; Jordà-Faus, Pepe; Chico-Mesa, Lorena; Cai, Jun; Chen, Yan-Xia; Rodes, Antonio; Feliu, Juan M.; Herrero, Enrique
Resumen: The formic acid oxidation reaction (FAOR) on bismuth-modified Pt(100) is studied using electrochemical techniques and FITR spectroscopy at different bismuth coverages and formic acid concentrations. The results clearly show that: (1) The measured currents for the Bi-modified Pt(100) surface contain contributions from both the Pt-Bi ensembles and the Pt sites far from the Bi adatoms. (2) The catalytic effect of bismuth is not linked to the adsorption of formate on Pt sites. (3) The bismuth not only improves the activity of the FAOR through the active intermediate but also inhibits the CO poison by a third-body effect. (4) The experimental results indicate that the catalytic activity is linked to the Pt-Bi ensembles. The active species, formate, adsorbs on the Bi site and the neighboring Pt sites facilitate the cleavage of the C-H bond. (5) From the concentration dependence, the reaction order for formate on bismuth-modified Pt(100) is 1 at low potentials. In contrast, a reaction order of 0.5 is obtained at higher potentials. These results are in agreement with the proposed mechanism.2023-07-05T00:00:00ZElectronic structure and experimental benchmarking of aluminum spinels for solar water splitting
http://hdl.handle.net/10045/134181
Título: Electronic structure and experimental benchmarking of aluminum spinels for solar water splitting
Autor/es: Pastor, Francisco J.; Contreras, Maxime; Lana-Villarreal, Teresa; Orts, José M.; Gómez, Roberto
Resumen: A computational methodology for screening aluminum-based spinel oxides for photoelectrochemical water splitting has been developed by combining HSE06 and PBE + U calculations. The method, which can be extended to other ternary oxides, provides values for formation energies, band gaps, band edge positions, and carrier effective masses. The formation energies indicate that the Al spinels of Mg, Co, Ni, and Zn (successfully synthesized using a sol-gel method) are among the most stable in the series. Except for the Mg and Zn cases, the electronic structures of the spinels are rather similar, with band gaps separating occupied and empty 3 d metal states. The charge-transfer band gap values are found to be above 3 eV, limiting the use of these materials in solar water splitting, although an estimate of the band edge positions indicates that, in general, both conduction band electrons and valence band holes can promote water reduction and oxidation, respectively. The effective masses of the charge carriers suggests that the spinels are n-type semiconductors as experimentally demonstrated. Importantly, both the UV–vis spectra and the photoelectrochemical results qualitatively agree with the theoretical electronic structure. In general vein, this work demonstrates the potential of theoretical screening for the development and selection of new photoelectrode materials based on ternary oxides for their application in solar water splitting.2023-05-02T00:00:00ZA stable anthraquinone-derivative cathode to develop sodium metal batteries: the role of ammoniates as electrolytes
http://hdl.handle.net/10045/129907
Título: A stable anthraquinone-derivative cathode to develop sodium metal batteries: the role of ammoniates as electrolytes
Autor/es: Ruiz-Martínez, Débora; Orts, José M.; Gómez, Roberto
Resumen: Rechargeable sodium metal batteries constitute a cost-effective option for energy storage although sodium shows some drawbacks in terms of reactivity with organic solvents and dendritic growth. Here we demonstrate that an organic dye, indanthrone blue, behaves as an efficient cathode material for the development of secondary sodium metal batteries when combined with novel inorganic electrolytes. These electrolytes are ammonia solvates, known as liquid ammoniates, which can be formulated as NaI·3.3NH3 and NaBF4·2.5NH3. They impart excellent stability to sodium metal, and they favor sodium non-dendritic growth linked to their exceedingly high sodium ion concentration. This advantage is complemented by a high specific conductivity. The battery described here can last hundreds of cycles at 10 C while keeping a Coulombic efficiency of 99% from the first cycle. Because of the high capacity of the cathode and the superior physicochemical properties of the electrolytes, the battery can reach a specific energy value as high as 210 Wh kg−1IB, and a high specific power of 2.2 kW kg−1IB, even at below room temperature (4 °C). Importantly, the battery is based on abundant and cost-effective materials, bearing promise for its application in large-scale energy storage.2022-11-26T00:00:00ZAdsorption of croconic acid anions at silver electrodes in sodium fluoride solutions. Interplay of DFT calculations and in situ ATR-SEIRAS measurements for the interpretation of experimental spectra of adsorbed species
http://hdl.handle.net/10045/129157
Título: Adsorption of croconic acid anions at silver electrodes in sodium fluoride solutions. Interplay of DFT calculations and in situ ATR-SEIRAS measurements for the interpretation of experimental spectra of adsorbed species
Autor/es: Cheuquepán, William; Rodes, Antonio; Orts, José M.
Resumen: The adsorption of species coming from the disodium salt of croconic acid (4,5-dihydroxy-4-cyclopentene-1,2,3-trione, H2C5O5) at chemically deposited silver electrodes was studied in aqueous sodium fluoride solutions by combining in situ ATR-SEIRAS (Surface-Enhanced Infrared Reflection Absorption Spectroscopy experiments under Attenuated Total Reflection conditions) and Density Functional Theory (DFT) calculations. Voltammetric experiments suggest the existence of reversible adsorption processes in the potential range between −0.55 and −0.20 V vs Ag/AgCl (KCl 1 M), whereas irreversible reduction is observed for potentials below-0.55 V. ATR-SEIRA spectra show potential-dependent adsorbate bands in the potential range for reversible adsorption, that were assigned according to DFT calculations. Calculated optimized geometry of adsorbed croconate and bicroconate correspond to bonding to the silver surface in a bidentate configuration through two oxygen atoms with the molecular plane perpendicular to the metal surface. The broadening and splitting at high electrode potentials of the Csingle bondO stretching bands for adsorbates coming from croconic acid can be explained by invoking the existence of collective vibrational modes appearing at high coverage. In overall, the ATR-SEIRA spectra obtained with Ag thin layer electrodes resembles that reported for Au thin layers. As a difference, higher adsorbate coverage seems to be obtained in the case of silver. Moreover, a strong feature at ca. 1580 cm−1 is experimentally observed, that was much weaker on gold samples. The calculated frequencies for adsorbed croconate and bicroconate do not change significantly with the adsorption bonding sites for the optimized geometries. Taking into account the calculated frequencies of both types of species, a better agreement with the experimental behavior (including the splitting/shifting caused by dipole–dipole coupling in high-coverage collective modes) is obtained in the case of bicroconate. The coexistence with some adsorbed croconate species cannot be ruled out.2022-10-30T00:00:00Z