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Supplementary information
Electrodeposited Cobalt Oxide Nanoparticles Modified Carbon Nanotubes as a Non-precious Catalyst
Electrode for Oxygen Reduction Reaction
Ahmed Zaki Al-Hakemya, Abu Bakr Ahmed Amine Nassrb1‫٭‬, Ahmed Hosny Naggara, Mohamed Salaheldin
Elnoubyb, Hesham Mohamed Abd El-Fattah Solimanb, Mahmoud Ahmed Taher a
a
Chemistry Department, Faculty of Science, Al-Azhar University, 71542 Assiut, Egypt
b
Advanced Technology and New Materials Research Institute (ATNMRI), City of Scientific Research and
Technological Application (SRTA-City), 21934 Alexandria, Egypt.
‫٭‬Corresponding author: AB.A.A. Nassr, Email: [email protected]
at the Advanced Technology and New Materials Research Institute (ATNMRI), City of Scientific Research and
Technology Application (SRTA-City), 21934 Alexandria, Egypt.
Tel: 0049 17651842598
Fax: +20 3 4593414
1
Current address: Electrochemistry Group, School of Chemistry, University of Southampton. Southampton
SO17 1BJ, UK
1. Functionalization of carbon nanotube and electrodeposition process
To confirm the functionalization process, the CNTs and FCNTs was investigated by cyclic voltammetry in 0.5 M
H2SO4. The voltammograms of both are shown in Fig. (S1), the CV of FCNTs displays a distinct redox peaks,
which are attributed to the electrochemical redox behavior for quinone (Q) hydroquinone (HQ), created on the
edges of the graphitic carbon in carbon nanotubes by the action of nitric acid oxidation. On the other hand, these
redox peaks didn’t detect in the CV of the as-received carbon nanotubes indicating that the oxidation of CNTs
with nitric acid was able to create oxygen-containing groups on the surface of carbon nanotubes [1,2]. Moreover,
the double capacitance region for the FCNTs is higher than that of the as-received one demonstrating the higher
defect sites on the FCNTs ]3[.
Figure SI 1: CV of as received and functionalized carbon nanotubes in 0.5 M H 2SO4 (scan rate 100 mVs-1).
In order to identify the best potential for electrodeposition process, The deposition potential has been selected
based on the initial CV recorded for FCNTs/GC in cobalt nitrate solution (Fig SI2 A). It is clear from the CV
that the reduction of Co2+ to Co starts at a potential lower than -0.07 V vs. SSC. Going to more negative
potential, the cathodic current reduction increase with a cathodic peak at -0.65 V vs. SSC indicating the higher
nucleation of Co deposited particles with maximum reduction power at this potential. With increasing the
potential more in the negative direction after the cathodic peak, the CV showed a steady current region
indicating that a more negative potential has no an effect to deposit more cobalt particles and the saturation of
the surface with particles. Increasing the potential more in the cathodic direction resulted in development of the
hydrogen evolution reaction (HER), which started at -0.94 vs. SSC as indicated by the sharp cathodic peak in the
figure (SI 2). On the reverse direction, a broad anodic peak at -0.34 V vs. SSC is detected which signed to the
dissolution of Co particles, i.e. oxidation of Co to Co 2+ ]4[. Moving towards more anodic potential, the current
increase sharply as the oxygen evolution reaction (OER) on formed higher oxidized CoO x particles is
pronounced. It is more important here to distinguish between the electrodeposition of CoO x on the FCNTs/GC
and on the GC directly as the presence of FCNTs enhances the electrodeposition of CoOx to start at lower
cathodic potential as given by the comparison the CV curves for the two cases demonstrating that the presence
of carbon nanotubes reduces the overpotential for electrodeposition of CoOx (Figure SI 2a, b).
Figure SI 2: CV of FCNTs/GC (A) and GC (B) in N2-saturated 2 mM Co(NO3)2·6H2O/0.1 M Na2SO4 (scan rate
100 mVs-1).
The current versus time curve for electrodeposition for 15 min is given in Fig. (SI 3 ) and the initial behavior is
given inside. In the first instant for beginning the electrodeposition process, the initial current is current for
charge the double layer and initiation of the electrodeposit process by the nucleation step. The cathodic current is
increased to reach its maximum indicating the growth of the nuclei after that it is decreased as a result of two
opposite effects; the growth of nuclei and saturation of the surface with deposited particles ]5[.
To calculate the amount of deposited species, the charge passing during electrodeposition was calculated from
the current versus time curve and the amount of deposited particles estimated from Faraday’s law (assuming the
100 % current efficiency) assuming that only the deposited species are only metallic Co. The amount of
deposited are tabulated in Table (SI1).
Figure SI 3: CA (current time) curve for electrodeposition of CoO x N2-saturated 2 mM Co(NO3)2·6H2O 0.1 M
Na2SO4 at -0.65 V vs SSC for 15 min on FCNTs/GC. Inside initial behavior and starting the deposition process.
Table SI 1 : Parameters for the deposition process and ORR kinetics .
Catalyst Electrode
Charge (mC)
Mass of deposit
(µg)
1CoOx/FCNTs
6.42
1.96
2CoOx/FCNTs
12.43
3.8
5CoOx/FCNTs
25.60
7.8
10CoOx/FCNTs
41.66
12.72
15CoOx/FCNTs
51.60
15.75
25CoOx/FCNTs
98.10
29.95
15 CoOx/GC
4.6
1.4
FCNTs/GC
Pt/C
10 a
a
the amount here refers to the amount of Pt in the electrode
2. Electrochemistry study
1- 1CoOx/FCNTs
E1/2
-0.17
-0.19
-0.16
-0.16
-0.16
-0.18
-0.18
0.012
Ik
(mA.cm-2)
05.5
03.5
05.9
07.2
07.7
04.8
00.2
04.0
59.6
2- 2CoOx/FCNTs
3- 5CoOx/FCNTs
4- 10CoOx/FCNTs
5- 25CoOx/FCNTs
6- Pt/C
Figure SI 3: CV (in N2 and O2) (a), LSV-RDE curves (b) in 0.1 KOH and K-L plots (c) for different
CoOx/FCNTs catalyst electrodes and Pt/C.
Figure SI 3: dependence the number of electron (n) calculated from K-L plot on the potential value in the
diffusion current region.
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