Carlota Domínguez

The development and commercialization of direct methanol fuel cells (DMFCs) as energy conversion devices remains a challenge despite their advantages in terms of energy density and energy‐conversion efficiency. The bottleneck for the development of DMFCs is mainly caused by the sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode of fuel cells, and the effect of the so‐called methanol crossover in state‐of‐the‐art Pt/C electrocatalysts. Herein, we report for the first time an easily scalable continuous flow method based on ultraspray pyrolysis (USP) for the preparation of Pt nanoparticles directly embedded on highly porous carbon spheres. A study on the effect that post‐synthesis treatment procedures have on the level of graphitization and catalytic properties is described. Use of USP results in a substantial reduction of the final Pt content with respect to typical Pt/C electrocatalysts, while yielding also excellent durability and tolerance to methanol crossover under acidic conditions. These results demonstrate that the USP method reported herein is a good candidate for its use in the preparation of ORR catalysts in commercial applications.

Solvothermally synthesised MnCO₃ leads to template-free formation of highly porous, defect-rich MnO₂ with high activity in water oxidation.

The electrooxidation of ethanol and acetaldehyde on Pt/C has been studied by using in situ IR spectroscopy. To identify the species formed during the electrooxidation reactions accurately, the IR spectra were collected in both HClO₄/H₂O and HClO₄/D₂O electrolytes. The results shown herein reveal that ethanol adsorbs on Pt at low potentials in a series of dehydrogenative steps that lead to η₂‐acetaldehyde prior to the scission of the C−C bond, which takes place at potentials higher than 150 mV. At potentials of approximately 220 mV, the Pt surface is fully covered by CO_ad (and C_1,ad) species, which thus impede further ethanol adsorption. At higher potentials, when OH_ad species are nucleated, CO_ad is oxidized to CO₂, which releases Pt sites for further ethanol adsorption and oxidation. However, due to the presence of OH_ad species, ethanol oxidation to acetic acid is the preferred reaction pathway. In contrast, the C−C bond of acetaldehyde is broken at 50 mV, which leads to the formation of a full monolayer of CO and CH_x adsorbed species on Pt. The IR spectra collected in an electrolyte that contained D₂O show no evidence for the formation of acetyl species prior to the scission of the C−C bond.

In this work a series of N–modified graphene composites with different N/C ratios have been synthesised. The incorporation of Fe atoms into the N–modified graphene composites leads to the formation of Fe/N/C ensembles on the outer graphene layers along with Fe₃C and metallic Fe phases in the bulk of the graphite nanoplates as revealed by X-ray absorption and XPS analyses. The adequate choice of the N/C atomic ratio of precursors to prepare Fe/N/graphene based materials is crucial to obtain electrocatalysts with an optimal performance for the ORR. The activity for the oxygen reduction reaction (ORR) of the Fe/N–graphene based electrocatalysts increases with increasing amount of accessible nitrogen, that is, with the amount of nitrogen by surface area.