Beatriz Ruiz Camacho

El desarrollo de electrocatalizadores libres de metales nobles con eficiencias superiores para catalizar la reacción de reducción de oxígeno (RRO), sigue siendo un desafío para la aplicación de celdas de combustible. En este trabajo se evaluaron electroquímicamente nanomateriales a base de oxido de grafeno dopado con nitrógeno y funcionalizados con cobalto (Co-N-GO) y hierro (Fe-N-GO) como electrocatalizadores catódicos para la RRO y la reacción de evolución de oxígeno (REO) en medio ácido. Se investigó el efecto del método de síntesis térmico (in-situ) e hidrotermal (post-síntesis), y el desempeño del metal de transición utilizado (Fe vs Co). La evaluación de la actividad electrocatalítica se efectuó mediante las técnicas electroquímicas de voltamperometría cíclica (CV) y voltamperometría lineal de barrido (LSV), arrojando una respuesta aceptable, con mejora en potencial de inicio y potencial de media onda cuando se incorpora el Fe y Co. Se encontró que los materiales sintetizados por el método in-situ presentan mayor potencial de inicio para la RRO. Por otro lado, para catalizar la REO, se encontró que el método más favorable es el post síntesis. Estos resultados indican que es posible obtener materiales específicos para una reacción en particular, seleccionando adecuadamente el método de síntesis, resultando así electrocatalizadores prometedores para los sistemas de conversión de energía.

The synthesis of metal‐free electrocatalysts for oxygen reduction reaction (ORR) in fuel cells has attracted remarkable attention. We report the synthesis of B, N, and BN co‐doped carbon materials by the hydrothermal method. The effect of surface oxygen on graphene oxide over the amount of N and B doping was investigated. Two types of carbon were evaluated: 1) commercial graphene oxide (GO _comm ) and 2) GO chemically modified. GO exhibited higher surface oxygen (27.16%) and structural defects (I _D /I _G = 0.97) after chemical modification, which favors the amount of heteroatom doping. The N‐doped carbon (N‐GO and N‐GO _comm ) showed a higher onset potential (E _onset ) than B‐doped carbon samples (B‐GO and B‐GO _comm ), which can be associated with the higher amount of N‐doping, N electronegativity, and N‐species obtained. The BN co‐doped GO showed a synergetic effect, increasing the limited and kinetic current density, and the number of electrons transferred closer to four ( n = 3.9 e‐). The presence of both N (pyridinic/quaternary) and B (BC ₃ ) heteroatoms increased the activity of B‐N‐GO for the ORR, showing a higher current density in both kinetic and mass transfer regions. This work provides new alternatives of an attractive electrocatalyst (B‐N‐GO) for ORR application.

In this work, a numerical analysis of three different flat plate solar collectors was conducted using their entropy generation rates. Specifically, the Computational Fluid Dynamics (CFD) technique was used to compare the detailed performance of conventional and zigzag tube geometries of flat plate solar collectors (FPCs) in terms of their entropy generation rates. The effects of fluid viscosity, heat transfer, and heat loss of the flat plate solar collectors were considered for the local and global entropy generation rate analyses. Variations on the inlet volumetric flow rate of the FPCs from 1.0 to 9.0 L/min were simulated under the average solar radiation for one year in the state of Guanajuato, Mexico. The results illustrate and discuss the temperatures, pressures, and global entropy generation rates for volumetric flow variations. The velocity, temperature, and pressure distributions and the maps of the local entropy generation rates inside the collectors are presented and analyzed for the case with a flow rate of 3.0 L/min. These results demonstrate that the zigzag geometries achieved higher outlet temperatures and greater entropy generation rates than the conventional geometry for all the volumetric flow rates considered.

It is well-known that γ-Al₂O₃ possesses large, specific areas and high thermal, chemical, and mechanical resistance. Due to this, it is the most-used support for catalysts, in this case TiO₂, as it enables it to achieve better dispersion and improves the activity in catalytic photodegradation reactions. In a previous work, it was observed that the optimal content of TiO₂ in γ-Al₂O₃ was around 15% since the degradation of phenol results were maximized and a synergistic effect was generated by the interaction of both oxides. In addition, an increase in acidity crystal size and the generation of localized, oxygen-vacant, electronic states in the forbidden band of γ-Al₂O₃, were observed. This study focuses on the effect of the calcination temperature on a γ-Al₂O₃-TiO₂ catalyst (15% w/w of TiO₂) and its impact on photocatalytic activity. The catalysts prepared here were characterized by X-ray diffraction, N₂ adsorption–desorption, FTIR-pyridine adsorption, MAS-NMR, HRTEM-FFT, UV-vis, and fluorescence spectroscopy.