Pietro P. Lopes

Complex Oscillatory Response of a PEM Fuel Cell Fed with H2 / CO and Oxygen

Oscillatory kinetics is commonly observed in the electrocatalytic oxidation of most species that can be used in fuel cell devices. Examples include formic acid, methanol, ethanol, ethylene glycol, and hydrogen/carbon monoxide mixtures, and most papers refer to half-cell experiments. We report in this paper the experimental investigation of the oscillatory dynamics in a proton exchange membrane (PEM) fuel cell at 30°C. The system consists of a Pt/C cathode fed with oxygen and a PtRu (1:1)/C anode fed with H 2 mixed with 100 ppm of CO, and was studied at different cell currents and anode flow rates. Many different states including periodic and nonperiodic series were observed as a function of the cell current and the H 2 /CO flow rate. In general, aperiodic/ chaotic states were favored at high currents and low flow rates. The dynamics was further characterized in terms of the relationship between the oscillation amplitude and the subsequent time required for the anode to get poisoned by carbon monoxide. Results are discussed in terms of the mechanistic aspects of the carbon monoxide adsorption and oxidation.

Eco-friendly synthesis of bimetallic AuAg nanoparticles

In this study we report a friendly route to produce colloidal AuAg bimetallic nanoparticles (NPs) using glycerol as a reducing chemical in alkaline medium. Ultraviolet spectroscopy (UV-Vis) and transmission electron microscopy (TEM) confirmed the formation of colloidal NPs. The nanoparticles were also directly produced on carbon to yield Au/C, Ag/C and AuAg/C. Extended X-ray absorption fine-structure (EXAFS) spectroscopy at the Au L3 edge evidenced surface segregation of silver in the AuAg/C material. Also the X-ray absorption near edge structure (XANES) region indicated a slight reduction in the Au 5d band occupancy due to the presence of silver. Since a fuel cell is a potent source of energy for the future, the catalytic properties of the NPs were investigated for anodic glycerol electro-oxidation reaction and results for AuAg NPs are compared with those for monometallic Au and Ag NPs. When compared with Au/C, the AuAg/C material displayed lower potential for glycerol electro-oxidation, reducing by 120 mV the onset potential for glycerol electro-oxidation. This means that the electro-oxidation of glycerol on the bimetallic catalyst is mainly affected by the ligand effect.

Complex Dynamics in a PEM Fuel Cell

Oscillatory kinetics in a polymer electrolyte membrane fuel cell (PEMFC) was studied at different applied currents and fluxes in the anodic compartment. The system consisted of a Pt/C cathode fed with oxygen and a PtRu(1:1)/C anode fed with H2 mixed with 108 ppm of CO, and was operated at 30 C. Many different states including periodic and non-periodic series were observed as a function of the applied current (j) and the H2/CO flux. In general, aperiodic/chaotic states were favored at high currents and low flux. This allowed us to discuss the connection between the observed dynamics and the reaction mechanism.

Real-time determination of CO2 production and estimation of adsorbate coverage on a proton exchange membrane fuel cell under oscillatory operation

A number of fuel cell relevant reactions are known to undergo kinetic instabilities under certain conditions. The majority of the experiments in such systems have been performed in liquid electrolyte systems on half-cell setups. Results for proton exchange membrane fuel cells fed with H2/CO mixtures at the anode show that there can be a range of gas flow rate and current density where spontaneous potential oscillations take place. Despite the recent developments in this area, there are still many mechanistic aspects underlying the emergence of electrochemical oscillations that remain unknown. In the present contribution, we report results on the CO2 production during the oxidation of carbon monoxide-containing hydrogen in a proton exchange membrane fuel cell, as measured by online mass spectrometry. By extensive fitting and careful consideration of the proposed mechanism, we were able to estimate the coverage of hydrogen and CO during the oscillations. As no other approach seems capable to probe the adsorbate coverage in an operando fuel cell, our analyses access experimental hidden information that can be of high value for fuel cell research.

Estudo do efeito de tratamentos térmicos em catalisadores de PtRu/C frente à reação de oxidação de hidrogênio na presença de CO

In this work the effects of time and temperature of thermal treatments under reducing atmosphere (H2) on PtRu/C catalysts for the hydrogen oxidation reaction (HOR) in the presence of CO on a proton exchange membrane fuel cell (PEMFC) single cells have been studied. It can be seen that the increase of the treatment temperature leads to an increasing sintering of the catalyst particles with reduction of the active area, although the catalyst treated at 550 oC presents more CO tolerance for the HOR.

PEMFC Oscillatory Behavior on a Pd-Pt/C Electrocatalyst

We have recently reported the emergence of spontaneous sustained potential oscillation in a PEMFC system fed with H2/CO on a PdPt electrocatalyst anode. When compared to previously observed oscillation in the PtRu anode, the oscillations in the former case where characterized by features such as lower frequency and higher amplitude. Herein we report a numerical study of this system and discuss the results in terms of the reaction mechanism, in connection with the data for PtRu. We found that the main oscillatory features could be linked to the material adsorptive and oxidative properties by combining CO stripping voltammetry, steady and oscillatory state data and kinetic simulation of the electrochemical reactions taking place at the PEMFC anode. We show that not only PtRu can prompt the emergence of such behavior, but also that some degradation aspects must be considered before making benefit from the higher power output generated in the oscillatory regime.