Tipos De Celdas

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 was from 100 kHz to

10 mHz. Impedance experiments were performed in the potentiostat/

galvanostat Voltalab model PGZ402.

3. Results and discussion

3.1. Morphological characterization

The morphology of Au particles was analyzed by TEM, Fig. 2a

shows the TEM image of Au particles (without carbon support).

Au particles form agglomerates of _20 nm in size, these agglomerates

are constituted by even smaller particles (crystallites) with an

approximate size of 7 nm. The diffraction pattern of Au nanoparticles

is shown in Fig. 2b, in this figure sharp and well-defined peaks

are observed. The sharpness of peaks indicates a high crystallinity

of Au nanoparticles. From the X-ray diffraction pattern in Fig. 2b,

the different crystallographic planes were identified, this was carried

out by comparing 2h angles with card JCPDS 04-0784 from diffractometer

´s software. Card JCPDS 04-0784 belongs to Au with a

face-centered cubic (FCC) structure. Following this procedure, the

planes Au(1 1 1), Au(2 0 0), Au(2 2 0), Au(3 1 1) and Au(2 2 2) were

identified. By using MDI Jade 5.0 software and XRD pattern, the Auparticle

size was obtained giving a value of _11.5 nm, this value

was also verified by using Scherrer’s equation on peak Au(1 1 1).

In order to observe the electrochemical response of Au particles

in acidic medium, different electrochemical tests were carried out.

2,1. Síntesis de Au electrocatalizador Partículas de Au se sintetiza a partir de la reducción de AuCl3 (Aldrich 99% de pureza) con NaBH4, (pureza Aldrich 98%) en tetrahidrofurano (THF) a temperatura ambiente. Esta metodología ha sido empleada en nuestro laboratorio para obtener diferentes electrocatalizadores metálicos

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