l O P Publishing | Vietnam Academy of Science and Technology Advances in Natural Sciences: Nanoscience and Nanotechnology
Adv Nat SCI . Nanosd. Nanolechnol. 6 (2015) 025012 (6^)) doi:l0.1088/2O43-626a6/2/025012
Preparation of the vulcan XC-72R-supported Pt nanoparticles for the hydrogen evolution reaction in PEM water electrolysers
Huy Du Nguyen', T Thuy Luyen Nguyen^ Khac Manh Nguyen', Thuc Huy Ha^ and Quoc Hien Nguyen^
' University of Science, Vietnam National Umversity in Ho Chi Minh City, 227 Nguyen Van Cu Street, Ho Chi Minh City, VieQiam
^ Research and Development Center for Radiation Technology. Vietnam Atomic Energy Commission, 202A, Street 11, Linh Xuan Ward, Thu Due District, Ho Chi Minh City, Vietnam
E-mail: hien7240238@yahoocom Received 14 January 2015 Accepted for publication 26 January 2015 Published 20 February 2015
CrossMark Abstract
Pt nanoparticles on vulcan XC-72R support (Pt/vulcan XC-72R) were prepared by the impregnation-reduction method. The Pt content, the morphological properties and the electrochemical catalysis of the Pt/vulcan XC 72R matenals have been investigated by ICP-OES analysis, FESEM, TEM, and cyclic voltanunetry. These materials were then used as catalyst for hydrogen evolution reaction at the cathode of proton exchange membrane (PEM) water electrolysers. The best catalyst was Pt/vulcan XC-72R prepared by the impregnation-reduction method which is conducted in two reducing steps with the reductants of sodium borohydride and ethylene glycol, respectively. The current density of PEM water electrolysers reached 1.0 A cm""^
when applying a voltage of 2.0 V at 25 "C.
Keywords: proton-exchange membrane, platinum nanoparticles, carbon support, impregnation- reduction method
Classification numbers: 4.02, 6.00
1. i n t r o d u c t i o n [1, 2]. The platinum and palladium nanoparticles supported by vuIcan-XC 72 [1] or graphitic nanofibers [2| have been Proton-exchange membrane (PEM) water electrolysis can successfully used as electrocatalysts at the cathode for HER.
contribute to the development of a hydrogen infrastructure However, it is not easy to fabricate the noble metal nano- network [1-3]. Hytlrogen can be produced efficientiy using particles spreading on the whole surface of the carbon carriers electricity from renewable energy sources such as solar and because the surface area of the carbon carriers is very large, wind [1, 2, 4]. In conventional PEM water electrolysers, e.g. 1 7 0 m ^ g " ' and 250m^g'"' for graphitic nano-fibers and precious metals have been used as electrocatalysts such as vulcan XC-72R, respectively. To date, the impregnation- platinum or palladium at the catiiode for the hydrogen evo- reduction method has been considered as the best method to lution reaction (HER) and iridium (or its oxides) at the anode prepare the noble metal nanoparticles on carbon carriers, for the oxygen evolution reaction (OER) [1, 2, 5]. One of the There are some impregnation-reduction methods using dif- main challenges in PEM technology is minimizing of noble ferent reductants such as formaldehyde (FD) [1, 2], ethylene metal loading in PEM cell witiiout decreasing its efficiency glycol (EG) [6], and sodium borohydride (SB) [7].
and lifetime. This can be achieved by using the electro- Therefore, the aim of this study is screening and catalysts consisting of the nanoparticles of the noble metals improvmg the impregnation-reduction method to prepare the on the low-cost electronic carriers with large surface area platmum nanoparticles on vulcan XC-72R carrier which is 2043-6262'i5/025012+O6S3300 1 © 2015 Vietnam Academy ot Science & Technology
^H
Adv. Nat. SCI Nanosci. Nanolechnol 6(2015)025012
Figure 2. FESEM image of catalyst; (a) Pt40/C (E), (b) Pt40/C (F); (c) Pt40/C (B) and (d) Pt40/C (2S).
Figure 3. TEM images of catalysts; (a) Pt40/C (E); (b) Pt40/C (F); (c) Pt40/C (B) and (d) Pt40/C (B-E).
Nanosci Nanotechnoi 6(2015)025012
(a)
•02 0 0.2 04 06 08 E(V]vs.Ag/AgCI,3MKCI
-02 0 02 04 06 08 10 IZ E(V)vs.AgfAgCI,3MKCi
.^M')
E(V)v5.Ag/AgCI,3MKCi
F>t«i«:(B.E| R black
E(V)V5.Ag/AgCI,3MKCi
Figure 4. Cyclic voltammograms recorded on electrodes modified by (a) Pt40/C (E), (b) Pt40/C (F), (c) Pt40/C (B) and (d) Pt40/C (B-E) and Pl black in 1 M H2SO4 at 25 °C, scan rate 20 mV s^\
size (figures 2(a) and (c)); the diameter of the Pt nanoparticles of small size is above 5 nm and the coverage ratios of Pt nanoparticles is not high (figures 3(a) and (c)).
Although the Pt nanoparticles of large size exist littie in the Pt40/C (B-E) catalyst (figure 2(d)), tiie diameter of the Pt nanoparticles of small size is below 3 nm and the coverage ratios of Pt nanoparticles are quite high (flgure 3(d)) There- fore, the decreasing of the loading of Pt (IV) salt also helps to lessen the diameter of the Pt nanoparticles on vulcan XC-72R.
On the other hand, the Pt40/C (F) catalyst only consists of a few Pt nanoparticles in large size (flgure 2(b)), the dia- meter of the Pt nanoparticles of small size is about 3 nm and the coverage ratios of Pt nanoparticles are quite high (figure 3(b)). Following image analysis, die Pt40/C (F) cata- lyst can be the best of the obtained catalysts. This obtained result is similar to the result reported by Grigonev et al [I].
The preeminence of FD reductant may be due to the absorption of FD on the Pt cluster [10] fonrung in the impregnation-reduction process. This absorption may prevent the Pt cluster from the size increasing.
3.3. Electrochemical characterization
Cyclic voltammograms recorded on the working electrode, which IS the glassy carbon electrode, are modified by the thin film of the Pt40/C catalysts and nation bmder. These cyclic voltammograms are shown in figure 4. The cychc voltam- metry curves of the Pt40/C catalysts are similar to that of Pt black powder catalyst (figure 4). Therefore, the Pt40/C cata- lysts are expected to behave as Pt black powder catalyst for tiie HER.
Electrochemically active surface areas (EAS) of the Pt40/
C catalysts were estimated from the cyclic voltammetry curves in figure 4 The EAS of tiie Pt40/C (F) catalysts is similar to Uie result obtained by Grigoriev et al [1]. The EAS
Table 2. The EAS of catalysts Catalyst
Pt black Pt40/C (E) Pt40/C (F) Pt40/C (B) Pt40/C (E-B)
Reductant
_
EG FD SB SB-EGSolvent
_
EG EG/H2O H2O H2O-EGEAS(m^g-') 16.5 ±2.0 27.0 ±2.5 37.0 ±3.0 25.5 ±2.5 35 5 ±4.0
of Pt40/C (F) catalysts is flie same as tiiat of the Pt40/C (B-E) catalyst and higher flian those of tiie Pt40/C (E), Pt40/C (B) or Pt black catalysts (table 2). Therefore, to enhance tiie EAS of the catalysts, the impregnation-reduction method is necessary to use FD reductant or decrease the loading of Pt (IV) salt in each impregnation-reduction step.
3.4. Water electrolysis
During PEM water electrolysis, the typical current-voltage curves are recorded at 25 "C and plotted in figure 5. All our PEM water electiolysers illustrated the current density of l . O A c m " when the applied voltages were about 2.0 V. So our PEM water electrolysers operate similarly to those designed by Grigoriev etal [11]. Thek conversion efficiency reaches about 7 5 % at 1.0 Acm~^ and 25 "C. Therefore, their conversion efficiency can show the cathodic catalysis of the synthesized Pt40/C catalyst.
The PEM electiolyser with tiie Pt40/C (B-E) catalyst at cathode offers the best efficiency (figure 5) in comparison with those with tiie other Pt40/C or Pt black catalyst at cathodic catiiode. Cathodic catalysis of the Pt40/C (F) catalyst was a little lower than tiie Pt40/C (B-E) catalyst, altiiough tiie Pt40/C (F) and Pt40/C (B-E) catalyst possess tiie same EAS.
This unexpected behavior could result from the absorption of
Adv. Nat SCI. Nanosci Nanotechnoi. 6 (2015) 025012
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Current densi^ (A.cm'
Figure 5. I-V polarization curves measured on a 1.0 cm^ single electrolysis cell at 25 "C and atmosphenc pressure. Cathodic catalyst; Pt40/C (2S), Pt40/C (F), Pt40/C (B), Pt40/C (E) and Pt black (1.25 mg cm~^). Anodic catalyst. Ir black (2.5 mg cm" ).
impregnation-reduction method consisting of two steps with tiie Pt loading about 20% of carbon weight per step is a promising approach for the preparation of the cathodic cata- lysts which possess Pt nanoparticles on vulcan XC-72R carrier.
Aciinowiedgments
This work is financially supported in part by the Department of Science and Teclmology of Ho Chi Mmh City, Vietiiam.
FD on tiie Pt nanoparticles of Pt40/C (F) catalyst [10]. Further study should be carried out to clarify this phenomenon.
4. Conciusions
The results show tiiat Pt40/C (F) has the highest coverage ratio and the Pt nanoparticles are almost those of homo- geneous size while the Pt40/C (B-E) catalyst has the highest cathode catalysis. These results lead to the conclusion that the
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