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Previous issue date: 2006-07-14 / This work presents oxygem reduction reaction (ORR) studies on platinum (Pt/C)
and platinum-chromium alloys containing 50% (PtCr/C) or 70% in chromium (Pt3Cr)
dispersed on high surface area, in acid aqueous solutions with and without metanol,
with cyclic voltammetry, chronoamperometry and rotating disk electrode techniques.
Electrochemical measurements have been also performed in a direct methanol unit
fuel cell. The electrocatalysts were characterized by energy dispersive X-ray (EDX)
and X-ray diffraction (XRD) analyses. The ORR studies in absence of methanol in
solution showed that chromium adittion does not change the reaction mechanism
observed on the Pt/C and the electrocatalytic activity increases in the order PtCr/C
< Pt/C < Pt3Cr/C. Such increase was attributed to a favourable interatomic distance
for O2 dissociative adsorption. The alloys showed higher tolerance to methanol
presence in solution than Pt, mainly the PtCr electrode due to smaller amount of
active sites to methanol adsorption with respect to Pt. In solutions containing low
concentration of methanol, the ORR mechanism was not affected by methanol
presence. The polarization curves recorded with the unit cell showed that na
increase in temperature results in an increase in the electrocatalitic activity of the
anode, as well as na increase in methanol diffusion through the Nafion® membrane
with consequent cathode depolarization. Furthermore, the system containing
Pt3Cr/C as cathodic electrode material presented the best electrochemical
performance, with power densities of ~ 55 mW cm-2, in contrast to ~ 40 mW cm-2 for
the unit cell with Pt/C cathode and ~ 20 mW cm-2 with PtCr/C. / This work presents oxygem reduction reaction (ORR) studies on platinum (Pt/C)
and platinum-chromium alloys containing 50% (PtCr/C) or 70% in chromium (Pt3Cr)
dispersed on high surface area, in acid aqueous solutions with and without metanol,
with cyclic voltammetry, chronoamperometry and rotating disk electrode techniques.
Electrochemical measurements have been also performed in a direct methanol unit
fuel cell. The electrocatalysts were characterized by energy dispersive X-ray (EDX)
and X-ray diffraction (XRD) analyses. The ORR studies in absence of methanol in
solution showed that chromium adittion does not change the reaction mechanism
observed on the Pt/C and the electrocatalytic activity increases in the order PtCr/C
< Pt/C < Pt3Cr/C. Such increase was attributed to a favourable interatomic distance
for O2 dissociative adsorption. The alloys showed higher tolerance to methanol
presence in solution than Pt, mainly the PtCr electrode due to smaller amount of
active sites to methanol adsorption with respect to Pt. In solutions containing low
concentration of methanol, the ORR mechanism was not affected by methanol
presence. The polarization curves recorded with the unit cell showed that na
increase in temperature results in an increase in the electrocatalitic activity of the
anode, as well as na increase in methanol diffusion through the Nafion® membrane
with consequent cathode depolarization. Furthermore, the system containing
Pt3Cr/C as cathodic electrode material presented the best electrochemical
performance, with power densities of ~ 55 mW cm-2, in contrast to ~ 40 mW cm-2 for
the unit cell with Pt/C cathode and ~ 20 mW cm-2 with PtCr/C.
| Identifer | oai:union.ndltd.org:IBICT/oai:tede2:tede/928 |
| Date | 14 July 2006 |
| Creators | Varela Júnior, Jaldyr de Jesus Gomes |
| Contributors | Tanaka, Auro Atsushi |
| Publisher | Universidade Federal do Maranhão, PROGRAMA DE PÓS-GRADUAÇÃO EM QUÍMICA/CCET, UFMA, BR, QUIMICA |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Format | application/pdf |
| Source | reponame:Biblioteca Digital de Teses e Dissertações da UFMA, instname:Universidade Federal do Maranhão, instacron:UFMA |
| Rights | info:eu-repo/semantics/openAccess |
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