Zarate Bonilla, Ximena

Hitherto, platinum (Pt) is the most active electrocatalyst for the oxygen reduction reaction (ORR) of the proton exchange membrane fuel cells (PEMFCs). Enhancing the performance and reducing the use of costly Pt is of great significance for the wider adoption of PEMFCs. The present research demonstrates in situ synthesized Pt nanocrystal immobilized with sub nanometer sized cobalt (Co) particles (≤ 0.3 nm) loaded on ketjenblack carbon (KB) support via a simple polyol method as a highly active ORR electrocatalyst. The as synthesized Pt4.1Co/KB catalyst featured a more positive halfwave potential of 0.925 V with a resultant of 1.8 times higher mass activity than Co free Pt/KB catalyst at 0.9 V in 0.1 M HClO4 and insignificant decay in ORR performance after 30,000 potential cycles. The excellent electrocatalytic performance of Pt4.1Co/KB has also been proven in a practical H2/air fuel cell, demonstrating a maximum peak power density of 1.08 W/cm2, comparable to the standard Pt/C-TKK (47 %) catalyst. The improved ORR performance of Pt4.1Co/KB is attributed to the incorporation of sub nanometer sized Co particles, which synergistically enhance the activity and stability. Computational studies using periodic density functional theory calculations also suggest that the integration of ultrafine Co nanoparticles shifted the Pt contribution to the density of states towards higher energy levels, thereby facilitating the ORR process for the Pt4.1Co/KB catalyst. This work provides a distinctive development of an efficient and robust ORR catalyst for advancing PEMFCs.

Organic solar cells (OSCs) are one of the best alternatives in the photovoltaic area. These devices convert directly sunlight into electrical current with reasonable efficiencies. The most important component of an OSC is the photoconductive active layer which can be made of small organic molecules. In this theoretical study, a quantum chemical approach was applied to calculate the properties such as the energy of Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO), LUMO-HOMO energy gap, and the theoretical1 H NMR chemical shifts (the latter only for one molecule) for four organic molecules that exist in the literature. The geometry optimization of the four small molecules and the corresponding calculations were performed using Gaussian 09 software by means of the Density Functional Theory (DFT) at the B3LYP/6-31G(d) theoretical level. All the reported experimental values given in the papers were compared with the obtained theoretical values via a linear regression analysis. Our computational study showed good agreement with the experimental data as the regression analysis showed a coefficient of determination greater than 0.99.

In this work, we fabricated a TiO2 thin film, and the same film was modified with an Anderson aluminum polyoxometalate (TiO2-AlPOM). Physical-chemical characterization of the catalysts showed a significant change in morphological and optical properties of the TiO2 thin films after surface modification. We applied the kinetic and isothermal models to the methylene blue (MB) adsorption process on both catalysts. The pseudo-second order model was the best fitting model for the kinetic results; qe (mg/g) was 11.9 for TiO2 thin films and 14.6 for TiO2-AlPOM thin films, and k2 (g mg-1 min-1) was 16.3 × 10-2 for TiO2 thin films and 28.2 × 10-2 for TiO2-AlPOM thin films. Furthermore, the Freundlich model was suitable to describe the isothermal behavior of TiO2, KF (5.42 mg/g), and 1/n (0.312). The kinetics of photocatalytic degradation was fitted using the Langmuir-Hinshelwood model; kap was 7 × 10-4 min-1 for TiO2 and 13 × 10-4 min-1 for TiO2-AlPOM. The comparative study showed that TiO2 thin films reach a 19.6% MB degradation under UV irradiation and 9.1% MB adsorption, while the TiO2-AlPOM thin films reach a 32.6% MB degradation and 12.2% MB adsorption on their surface. The surface modification improves the morphological, optical, and photocatalytic properties of the thin films. Finally, the DFT study supports all the previously shown results. © 2023 The Authors. Published by American Chemical Society

A novel MOF named [Zn2(L)(DMF)] was synthesized using solvothermal methods from the reaction of the new linker (4,4′,4′′-(4,4′,4′′-(benzene-1,3,5-triyltris(methylene))tris(3,5-dimethyl-1H-pyrazole-4,1-diyl))tribenzoic acid) and Zn(NO3)2·6H2O. This new MOF was characterized by means of different techniques: powder X-ray diffraction, N2 adsorption and desorption isotherms, thermogravimetric analysis, and scanning electron microscopy. Furthermore, suitable crystals were obtained, which allowed us to perform the X-Ray structure determination of this MOF. The capability of these new MOF to adsorb CO2 at different temperatures was measured and its isosteric enthalpy of adsorption was calculated. The novel MOF shows an uncommon node composed of a Zn3(-COO)6(DMF)2, and the asymmetric unit contains one crystallographically independent linker, one DMF molecule, and two Zn atoms. The [Zn2(L)(DMF)] MOF is a microporous material with high crystallinity and stability up to 250 °C. The multiple nitrogenated pyrazole linkers in its framework enhance its CO2 adsorption capabilities. This material exhibits a low CO2 isosteric enthalpy of adsorption (Hads), comparable to previously reported values for similar nitrogenated materials. All the observed CO2 adsorption capacities were further supported by DFT calculations.

N-Doped TiO2 coatings (N-TiO2) were synthesized and characterized. The effect of the doping process on the physical-chemical properties and photocatalytic efficiency of Methylene Blue (MB) under visible light irradiation were studied. The bare TiO2 showed only anatase crystalline structure. Furthermore, after the doping process, a slight transition from anatase to rutile was verified. The HRXPS confirmed that the doping process was effective. The N2 sorption using the BET assay showed a slight increase in surface area after the doping process. MB adsorption kinetic showed also a slight increase for doped TiO2 films, showing as best fitting the Langmuir model. Furthermore, a modification on the electronic structure was observed, showed by the modification of the optical absorption profile in the doped material. The results showed that the MB adsorption on N-TiO2 thin films was endothermic (▵H=11 kJ mol−1) and a spontaneous process (▵G=−6.45 kJ mol−1). We performed DFT calculations to three simulated doped-structures. The Gap value, the global reactivity indexes and, the Fukui function isosurfaces are presented. Finally, the scavenger tests suggested that (Formula presented.) and OH⋅ could be the main ROS driving the photocatalytic process.

Hydrogen production is gaining interest as a clean energy source, with photocatalytic water-splitting being a key method due to its eco-friendly nature. Metalloporphyrins-based MOFs (TCPP(M)-MOFs), due to their tunable optical properties, are excellent materials for hydrogen evolution via water-splitting using sunlight. In this research, TCPP(M)-MOFs containing nodes based on metal ion d10 Zn2+ and TCPP(M) as linkers (M = Fe2+, Ni2+, Co2+and Cu2+) has been studied using theoretical approach. The electronic structure and optical properties of all Zn-TCPP(M)-MOFs were investigated using the density functional theory (DFT) and periodic-DFT calculations. The study revealed a bandgap reduction related to the open-shell metals in the TCPP linker, with an optimal value for the photocatalytic process under sunlight. TD-DFT calculations show that the inclusion of open shell ions enhances the linker-centered ligand-to-metal charge transfer process. Finally, it was suggested some directions for the design of new melloporphyrine-based MOFs, potentially leading to new materials for photocatalytic water-splitting.