Tipos De Celdas
Enviado por shanont • 7 de Noviembre de 2012 • 23.966 Palabras (96 Páginas) • 466 Visitas
Electroquímica análisis de la cinética y el mecanismo del oxígeno reducción de la reacción en nanopartículas de oro
Morphological characterization
Au particles were morphologically characterized by TEM and
XRD. TEM characterization was performed in a Philips XL 30 microscope.
X-ray experiments were performed in a Brucker 2000 diffractometer
with a step scan of 0.02_ 2h and 15 s per step,
between 30_ and 90_ 2h, at 35 kV and 30 mA, using Cu Ka radiation,
1.54056 Å. The data base (JCPDS) included in the diffractometer’s
software was employed to identify the crystallographic planes of
Au particles.
La caracterización morfológica Partículas de Au se caracteriza morfológicamente por TEM y DRX. Caracterización de TEM se realizó en un Philips XL 30 microscopio. De rayos X experimentos se realizaron en un difractómetro Brucker 2000 con una exploración paso de 0,02? 2h y 15 s por paso, entre 30? y 90? 2 h, a 35 kV y 30 mA, usando radiación Cu Ka, 1,54056 Å. La base de datos (JCPDS) incluido en el de difractómetro software se emplea para identificar los planos cristalográficos de Au partículas.
2.1. Synthesis of Au electrocatalyst
Au particles were synthesized from AuCl3 reduction (Aldrich
99% purity) with NaBH4, (Aldrich 98% purity) in Tetrahydrofurane
(THF) at room temperature. This methodology has been employed
in our laboratory to obtain different metal electrocatalysts with
particle size between 3 and 20 nm [30,31].
2.2. Morphological characterization
Au particles were morphologically characterized by TEM and
XRD. TEM characterization was performed in a Philips XL 30 microscope.
X-ray experiments were performed in a Brucker 2000 diffractometer
with a step scan of 0.02_ 2h and 15 s per step,
between 30_ and 90_ 2h, at 35 kV and 30 mA, using Cu Ka radiation,
1.54056 Å. The data base (JCPDS) included in the diffractometer’s
software was employed to identify the crystallographic planes of
Au particles.
2.3. Working electrode preparation and electrochemical
characterization
2.3.1. Working electrode
Au particles were mixed with an appropriate quantity of carbon
Vulcan XC-72–20% w/w. Ethanol (1:30 w/w) and ionomer Nafion
(1:30 w/w) were added to this mix, the suspension (ink) was
placed in ultrasonic bath for 10 min until a homogeneous solution
was obtained. An aliquot of 4 lL of this ink were applied on a
glassy carbon electrode with geometric area = 0.126 cm2 and was
left to dry for 24 h. The final catalyst loading of Au in the catalyst
layer was 0.71 mg/cm2.
2.3.2. Electrochemical characterization
All experiments were carried out in a three-electrode
electrochemical cell. Potentials were determined using a
mercury–mercurous sulfate (Hg/Hg2SO4/0.5 M H2SO4, E = 0.68 V
vs. NHE) reference electrode, and all the potentials were translated
to the normal hydrogen electrode (NHE) scale; a Pt mesh was used
as counterelectrode. Before any experiment, 10 cycles using cyclic
voltammetry were carried out in order to clean the working electrode
and activate the Au particles. The potential scan was initiated
at open circuit potential (EOCP _0.84 V vs. NHE) to _0.12 V vs. NHE.
The working solution was prepared from deionized water and
H2SO4 from Aldrich. Prior to experiment, the working solution
was bubbled with O2 during 15 min. Cyclic voltammetry experiments
were performed in a potentiostat/galvanostat Voltalab 100
model PGZ402. The rotating ring-disk electrode (RRDE) consisted
in a glassy carbon disk (diameter = 0.45 mm) and an Au ring sealed
in a polytetrafluoroethylene holder, the RRDE was polished with
alumina (0.05 lm), subsequently it was cleaned in an ultrasonic
bath in deionized water for 5 min. The potential scan was from EOCP
to _0.12 V vs. NHE, the scan rate was 3 mV/s and applying a constant
potential of 1.4 V vs. NHE to the ring, this was done in order
to oxidize the H2O2 produce on Au particles [20].
2.3.3. Impedance characterization
Impedance spectra of Au particles supported in carbon Vulcan
XC-72 were obtained at different dc potentials (E), after prepolarization
at the same potential by 120 s. During the whole experiment
the working electrode was rotating at 1000 rpm. Prepolarization
and electrode rotation are necessary in order to establish a pseudo
steady-state before impedance data acquisition. The used values of
E were: 0.63 V, 0.58 V, 0.53 V, 0.43 V, 0.38 V, 0.28 V, 0.18 V and
0.08 V vs. NHE. The amplitude of the signal perturbation was
10 mV, the frequency range scanned
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