Augusto César Azevedo Silva

In this study, we report the synthesis, characterization, and performance evaluation of a series of bimetallic Pt_xRh_y/C electrocatalysts with systematically varied Rh content for glycerol electrooxidation in acidic and alkaline media. The catalysts were prepared via a polyol reduction method using ethylene glycol as both a solvent and reducing agent, with prior functionalization of Vulcan XC-72 carbon to enhance nanoparticles (NPs) dispersion. High-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) analyses indicated the spatial co-location of Rh atoms alongside Pt atoms. Electrochemical studies revealed strong composition-dependent behavior, with Pt₉₅Rh₅/C exhibiting the highest activity toward glycerol oxidation. To elucidate the origin of raised results, density functional tight binding (DFTB) simulations were conducted to model atomic distributions and evaluate energetic parameters. The results showed that Rh atoms preferentially segregate to the surface at higher concentrations due to their lower surface energy, while at low concentrations, they remain confined within the Pt lattice. Among the series, Pt₉₅Rh₅/C exhibited a distinctively higher excess energy and less favorable binding energy, rationalizing its lower thermodynamic stability. These findings reveal a clear trade-off between catalytic activity and structural durability, highlighting the critical role of the composition and nanoscale architecture in optimizing Pt-based electrocatalysts for alcohol oxidation reactions.

Based on theoretical simulations, the best design for obtaining AgPt nanostructures (nanoshells with hollow interior) was unraveled that could exhibit methanol tolerance for oxygen reduction reaction (ORR) that occurs during direct methanol fuel cells (DMFCs) operation. A theoretical investigation of Pt@Ag and Ag@Pt core‐shell nanoparticles and AgPt nanoshells′ interaction with oxygen and methanol revealed that the oxygen interaction is significantly more favorable on AgPt nanoshells′ surface, hindering the methanol oxidation reaction (MOR) due to the random arrangement of Ag and Pt atoms. Experimentally, the nanoshells were prepared by a galvanic substitution and immobilized them onto silica, and the material was finely understood by associating electrochemical and physicochemical studies. Cyclic voltammetry showed the reduction and oxidation processes of the catalyst‘s species; however, XPS precisely showed that significant amounts of oxidized species were present (60.5 % of Ag⁰ and 39.5 % of Ag⁺, and 55.1 % of Pt⁰ and 44.9 % of Pt⁺²), which could affect the performance of the material. Indeed, the catalyst showed an excellent performance to ORR; the system yielded a 4‐electron ORR mechanism with just 1.0 wt.% Pt loading, with significant stability after 1000 runs. In addition, Koutecky‐Levich and Tafel plots assisted in understanding better the mechanism on the catalyst‘s surface, suggesting a first‐electron transfer for the rate‐determining step. Also, the catalyst resistance to the methanol crossover, theoretically simulated and predicted, was tested, showing remarkable tolerance for the alcohol up to a concentration of 2 M. Hence, a cathode catalyst with improved selectivity, low metal loading, high stability, and easy preparation was obtained.

Density functional theory based calculations were performed to study the modification of the electronic and structural properties originating from the interaction between the (10,0) GaPNT and the FeCl₃ and CrO₃ compounds, using the software SIESTA. The results show that, for both compounds interacting with the GaPNT, the structures remained practically the same with a small deformation. In all studied systems, FeCl₃ acts as an acceptor of electrons while CrO₃ as an electron donor. The binding energy showed that both the FeCl₃ and CrO₃ compounds interact strongly with the GaPNT through a chemisorption process. Projected density of states analysis shows that the electronic properties were drastically modified with the adsorption of the FeCl₃ compound on the GaPNT due to the appearance of localized states in the gap region. In all systems, the band gap was reduced except in the case of CrO₃ adsorbed outside the GaPNT, in which the band gap was increased. In the case of FeCl₃ adsorbed inside the GaPNT, the system became metallic, while all the other systems remained semiconductors.