Claudia D'Urso

Synthesis of Pd3Co1@Pt/C Core‐Shell Catalysts for Methanol‐Tolerant Cathodes of Direct Methanol Fuel Cells

A composite Pd-based electrocatalyst consisting of a surface layer of Pt (5 wt.%) supported on a core Pd3Co1 alloy (95 wt.%) and dispersed as nanoparticles on a carbon black support (50 wt.% metal content) was prepared by using a sulphite-complex route. The structure, composition, morphology, and surface properties of the catalyst were investigated by XRD, XRF, TEM, XPS and low-energy ion scattering spectroscopy (LE-ISS). The catalyst showed an enrichment of Pt on the surface and a smaller content of Co in the outermost layers. These characteristics allow a decrease the Pt content in direct methanol fuel cell cathode electrodes (from 1 to 0.06 mg cm(-2)) without significant decay in performance, due also to a better tolerance to methanol permeated through the polymer electrolyte membrane.

Selectivity of Direct Methanol Fuel Cell Membranes.

Sulfonic acid-functionalized polymer electrolyte membranes alternative to Nafion® were developed. These were hydrocarbon systems, such as blend sulfonated polyetheretherketone (s-PEEK), new generation perfluorosulfonic acid (PFSA) systems, and composite zirconium phosphate–PFSA polymers. The membranes varied in terms of composition, equivalent weight, thickness, and filler and were investigated with regard to their methanol permeation characteristics and proton conductivity for application in direct methanol fuel cells. The behavior of the membrane electrode assemblies (MEA) was investigated in fuel cell with the aim to individuate a correlation between membrane characteristics and their performance in a direct methanol fuel cell (DMFC). The power density of the DMFC at 60 °C increased according to a square root-like function of the membrane selectivity. This was defined as the reciprocal of the product between area specific resistance and crossover. The power density achieved at 60 °C for the most promising s-PEEK-based membrane-electrode assembly (MEA) was higher than the benchmark Nafion® 115-based MEA (77 mW·cm−2 vs. 64 mW·cm−2). This result was due to a lower methanol crossover (47 mA·cm−2 equivalent current density for s-PEEK vs. 120 mA·cm−2 for Nafion® 115 at 60 °C as recorded at OCV with 2 M methanol) and a suitable area specific resistance (0.15 Ohm cm2 for s-PEEK vs. 0.22 Ohm cm2 for Nafion® 115).

Investigation of IrO2/Pt Electrocatalysts in Unitized Regenerative Fuel Cells

IrO2/Pt catalysts (at different concentrations) were synthesized by incipient wetness technique and characterized by XRD, XRF, and SEM. Water electrolysis/fuel cell performances were evaluated in a 5 cm2 single cell under Unitized Regenerative Fuel Cell (URFC) configuration. The IrO2/Pt composition of 14/86 showed the highest performance for water electrolysis and the lowest one as fuel cell. It is derived that for fuel cell operation an excess of Pt favours the oxygen reduction process whereas IrO2 promotes oxygen evolution. From the present results, it appears that the diffusion characteristics and the reaction rate in fuel cell mode are significantly lower than in the electrolyser mode. This requires the enhancement of the gas diffusion properties of the electrodes and the catalytic properties for cathode operation in fuel cells.

Composite Anode Catalysts Based on PtRu and Metal Oxide Nanoparticles for DMFCs

A composite anode was investigated with the aim of enhancing the performance of direct methanol fuel cells (DMFCs). Fine iridium oxide nanoparticles were synthesized by a sulfite complex method. These IrO2 nanoparticles were mixed by sonication with a 50% PtRu/C catalyst prepared by the same procedure, considered as benchmark anode catalyst. A significantly higher performance was recorded for the composite electrode compared to the bare one based only on PtRu/C. The results confirm that the electrocatalytic activity is related to the characteristics of water displacement of the additive, evidencing that a multifunctional catalyst can operate better than PtRu for methanol oxidation since this multi-step process requires different functionalities to speed up the reaction rate.