Papers by Fernando Garzón
We report the first observation of terahertz emission from unbiased YBazCu307 thin films at room ... more We report the first observation of terahertz emission from unbiased YBazCu307 thin films at room tem-perature excited by 1.5 eV femtosecond laser pulses. The strength of the radiated terahertz field depends on the incident angle (8) and depends linearly on incident power. The ...
It is generally accepted that Pt-Ru alloy catalysts with an atomic Pt-to-Ru ratio of 1:1 generate... more It is generally accepted that Pt-Ru alloy catalysts with an atomic Pt-to-Ru ratio of 1:1 generate the best anode perform'ance in the direct methanol fuel cell (DMFG). However, at near-ambient cell operating temperatures, Gasteiger et al. reported that a catalyst with significantly lower Ru content, 10 at %, offers the highest activity towards methanol. Recently, Dinh et al. demonstrated that the activity of different Pt-Ru catalysts with the same Pt-to-Ru atomic ratio in the bulk might vary depending on the actual surface composition, which is often significantly different from that in the bulk phase, In this work, we study several experimental Pt-Ru catalysts (Johnson Matthey) with Pt-to-Ru atomic ratio ranging from 9: 1 to 1 :2. Electrocatalytic activity of these catalysts in methanol oxidation reaction is investigated in a regular DMFC 'and probed using voltammetric stripping of surhce CO.
ABSTRACT Polymer electrolyte membrane (PEM) fuel cells are currently being developed for transpor... more ABSTRACT Polymer electrolyte membrane (PEM) fuel cells are currently being developed for transportation and stationary applications. Since fossil fuels account for greater than 85% of our total energy consumption, 1 much research is being conducted to optimize low cost fuel reformer systems that convert this fuel (natural gas, petroleum or methanol) to hydrogen. 2 This hydrogen gas typically feeds a PEM fuel cell stack utilizing platinum based anodes. However, low concentrations of carbon monoxide (~ 10-100ppm) impurities in hydrogen can severely degrade the performance of PEM fuel cell anodes due to the strong adsorption of carbon monoxide on the electro-active platinum surface sites where hydrogen is normally oxidized to protons. 3 Therefore, detection and measurement of carbon monoxide in high temperature reformate streams is of vital importance to the successful implementation of fuel cells. 4 Current reformer systems that process hydrocarbon fuels utilize multiple reforming steps in order to reduce the CO concentration in the hydrogen fuel to < 10ppm. The hydrocarbon fuel is first subject to a combination of steam reforming and partial oxidation that results in a fuel with 15-25% CO content. This fuel then undergoes a water gas shift reaction that decreases the CO content to approximately 1%. Finally the fuel is sent through a preferential oxidation (PrOx) reactor where the CO content is reduced to < 10ppm. The optimization of the reforming process and the operation of the fuel cell can benefit greatly from the availability of CO sensors that can accurately measure the CO concentration in hydrogen containing streams in real time. In this paper we present the development of both PEM-based and oxide-based CO sensors for PEM fuel cell applications. The oxide-based carbon monoxide sensors utilize the difference in electrode kinetics of various metal/ electrolyte (oxygen-ion conducting) interfaces. Hashimoto et. al. have reported a fuel-cell type CO sensor that can measure CO concentrations in a hydrogen stream. 4 In this paper we will discuss the performance of various ceria and zirconia electrolyte based sensors using Ni, Pt and Pd as electrodes. A Pd/YSZ/Ni sensor had a response of 60mV to 100ppm CO at 185 o C. However, the response of all these sensors were found to decay over time due to some irreversible CO poisoning of the electrodes.
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Papers by Fernando Garzón