Available online at www.sciencedirect.com
ScienceDirect
Energy Procedia 63 (2014) 4031 – 4034
GHGT-12
Electrochemical detection of underwater CO2 using aminefunctionalized electrode
Hiroshi Sato*
Research Laboratory, IHI Corporation, 1, Shin-nakahara-cho, Isogo-ku, Yokohama 235-8501, Japan
Abstract
In this paper, fabrication of amino group-modified sensor electrode and electrochemical detection of CO2 in the saline solution
will be reported. Electrochemical detection of CO2 was carried out using cyclic voltammetry technique in redox active potassium
ferricyanide aqueous solution. Peak currents of oxidation and reduction reaction in cyclic voltammograms have changed
according to the concentration of CO2 molecules in the measurement solutions. The calibration curve for the CO2 concentration
was obtained by plotting oxidation peak currents. The sensor electrode prepared in this study can estimate differences between
the concentration of CO2 in normal seawater and that of up to 20 times.
© 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
© 2013 The Authors. Published by Elsevier Ltd.
(http://creativecommons.org/licenses/by-nc-nd/3.0/).
Selection and peer-review under responsibility of GHGT.
Peer-review under responsibility of the Organizing Committee of GHGT-12
Keywords: Carbon dioxide; Seawater; Electrochemical detection; Chemical sensor; Functionalized electrode
1. Introduction
Carbon Capture and Storage (CCS) technologies have received considerable attention because of the possible
applications to prevent global warming by reducing greenhouse gas such as carbon dioxide (CO2) [1]. The CCS
process consists of four processes of the capture process, the transportation process, the injection process, and the
storage process. In these processes, the storage process takes the longest period of the whole CCS process. Because
of that, long-term maintenance and monitoring is required to guarantee of safety.The detection technique of CO2
which exists in underwater environment is one of the key component technologies required for practical application
of CCS process. In order to perform continuous monitoring of underwater CO 2 in ocean storage parts, indirect
* Corresponding author. Tel.: +81-45-759-2819; fax: +81-45-759-2208.
E-mail address: hiroshi_sato@ihi.co.jp
1876-6102 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/3.0/).
Peer-review under responsibility of the Organizing Committee of GHGT-12
doi:10.1016/j.egypro.2014.11.434
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Hiroshi Sato / Energy Procedia 63 (2014) 4031 – 4034
detection techniques, such as pH measurement, have been used commonly. For the future, however, direct detection
technique will be required for performing more precise and sensitive monitoring of underwater CO 2.
Chemical sensors are applied to many scientific and industrial fields, such as medical treatment, food and
environmental monitoring; because of the sensor has high sensitivity and selectivity. The chemical sensor consists
from two parts: the detector part and the transducer part. Detector parts recognize the molecules to be measured by
functional organic groups. On the other hand, transducer parts convert molecular recognitions to signals such as
electrochemical signals, surface plasmon resonance, change of mass, etc. Since surface modification techniques for
the surface of the electrode are very common, electrochemical measurement is widely used for transducer part.
It is known that organic molecules having amino groups can react with CO 2 molecules forming carbamate ions.
Recently, for example, various alkanolamines and its blends have been studied as solvents for capture process of
CCS [2−4]. It is supposed to be able to fabricate a chemical sensor that can directly measure CO2 molecules using
amino groups as a detector part of the sensor. In this paper, electrochemical detection of CO2 in the saline solution
using amine-functionalized electrode will be reported. Electrochemical responses were measured in order to evaluate
combinations of CO2 molecules to the amino groups immobilized on the surface of the electrode. The calibration
curve is obtained by plotting electrochemical responses for CO 2 concentration.
2. Materials and Methods
2.1. Reagents
Aminoethantiol and potassium hexacyanoferrate (III) were purchased from Tokyo Kasei Co. (Tokyo, Japan) and
Kanto Kagaku Co. (Tokyo, Japan), respectively. Sodium chloride and Sodium bicarbonate were obtained from
Showa kagaku Co. (Tokyo, Japan). All the materials were of the highest grade available and were used as received.
2.2. Preparation of Amine-modified Electrodes
A gold (Au) disk electrode (diameter, 3.0 mm) was used. First, the surface of the electrode was polished
thoroughly with aqueous slurries of alumina paste and then rinsed with water, gently. The Au electrode was dipped
in a freshly prepared aminothiol aqueous solution (10 mM) overnight to fabricate self-assembled monolayer (SAM)
which has amino groups in the end of molecular chain, and then the electrode was rinsed with water, gently.
Detector part of
chemical sensor
Fig. 1. Fabrication of amino group terminated SAM on the Au electrode; immersion set-up
of the electrode (left) and surface of the electrode immersed overnight (right).
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Hiroshi Sato / Energy Procedia 63 (2014) 4031 – 4034
2.3. Electrochemical Evaluations
Electrochemical measurements of the amine-functionalized electrode were carried out on a conventional threeelectrode system using a platinum wire as the counter electrode and an Ag/AgCl electrode as the reference electrode.
All measurements were performed at room temperature.
working electrode
(sensor electrode)
K3[Fe(CN)6]
(redox active material)
counter electrode
(Pt wire)
reference electrode
(Ag/AgCl electrode)
CO2
(as NaHCO3)
Fig. 2. Experimental set-up for electrochemical evaluations of the sensor electrode.
As a measurement solution of electrochemical evaluations, an aqueous solution containing potassium
hexacyanoferrate (III) (5 mM) and sodium bicarbonate (0 to 50 mM) was prepared using a 500 mM sodium chloride
aqueous solution. Concentrations of CO2 solved in the solution were adjusted by changing the concentration of
sodium bicarbonate, which can produce CO2 molecules by their chemical equilibrium in an aqueous solution as
shown below.
ܰܽ‫ܱܥܪ‬ଷ ሺ‫ݏ‬ሻ ื ܰܽା ൅ ‫ܱܥܪ‬ଷି
‫ܱܥܪ‬ଷି ൅ ‫ ܪ‬ା ื ‫ܪ‬ଶ ‫ܱܥ‬ଷሺܽ‫ݍ‬ሻ
‫ܪ‬ଶ ‫ܱܥ‬ଷ ሺܽ‫ ݍ‬ሻ ื ‫ܪ‬ଶ ܱ ሺܽ‫ ݍ‬ሻ ൅ ‫ܱܥ‬ଶ ሺܽ‫ݍ‬ሻ
(1)
(2)
(3)
3. Results and discussions
Electrochemical detection of CO2 was carried out using cyclic voltammetry technique in redox active potassium
ferricyanide aqueous solution. Figure 3 shows cyclic voltammograms (CVs) and the calibration curve obtained. As
shown in the left part of Figure 3, oxidation and reduction current of the ferricyanide anions were obtained.
Moreover, both peak currents of oxidation and reduction have changed according to the concentration of the added
sodium bicarbonate; increasing concentrations of CO2 molecules by adding sodium bicarbonate leads decreasing of
both oxidation and reduction peak currents. The calibration curve for the CO2 concentration (shown in the right part
of Figure 3) was obtained by plotting oxidation peak currents of CVs. As shown in the plot, it is clear that the sensor
electrode prepared in this study can detect differences between normal concentration of CO2 in seawater (0.25 ppm)
and 10 times or 20 times higher concentration of that.
The mechanisms of change in electrochemical responses depending CO 2 concentration of the measurement
solutions, are illustrated in Figure 4. In the case of absence of CO 2 molecules (left part of Figure 4), ferricyanide
anions can diffuse to electrode surface easily, due to the amino groups which are neutral in their equilibrium.
However, in the case of presence of CO 2 molecules (right part of Figure 4), negative-charged carbamate anions are
produced by combining CO2 and amino groups on the electrode surface. Then, by the electrostatic repulsion
between ferricyanide and carbamate anions, it is expected that oxidation and reduction current are decreased.
Hiroshi Sato / Energy Procedia 63 (2014) 4031 – 4034
80
0 mM NaHCO3
2 mM NaHCO3
5 mM NaHCO3
10 mM NaHCO3
20 mM NaHCO3
30 mM NaHCO3
40 mM NaHCO3
60
Current / PA
40
20
90
oxidation peak current
0.25 ppm CO2
(normal seawater)
80
decrease
Current response / PA
4034
0
-20
-40
70
2.5 ppm CO2
(x10)
5 ppm CO2
(x20)
60
50
-60
y = -8.764ln(x) + 67.703
R² = 0.9943
40
-80
-0.4
-0.2
0
0.2
0.4
Potential / V vs. Ag/AgCl
0.6
0.1
0.8
1
Concentration of CO2 / ppm
10
Fig. 3. Cyclic voltammograms of amino group-modified sensor electrodes at 100 mV s-1 of scan rate (left)
and the calibration curve obtained by plotting electrochemical responses for CO2 concentration (right).
Carbamate ions
Amino groups
Surface of
the electrode
Fe(II)(CN)64-
CO2
Fe(II)(CN)64-
eFe(III)(CN)63-
Fe(III)(CN)63-
Fig. 4. Schematic illustrations of electrochemical reactions on the electrode surface
at absence (left) and presence (right) of CO2 molecules in the solution.
4. Conclusions
Electrochemical detection of CO2 in the saline solution was performed using amino group-modified Au electrode.
Oxidation and reduction current of the ferricyanide anions changed depending on the concentration of CO 2
molecules in the measurement solutions. The sensor electrodes prepared in this study are able to estimate
differences between the concentration of CO2 in normal seawater and that of up to 20 times.
References
[1] IEA, CCS 2014, Insight series 2014. http://www.iea.org/publications/insights/insightpublications/Insight_CCS2014_FINAL.pdf.
[2] Sato H, Yoshihisa K, Kubota N, Takahashi K, Matsumoto A, Yamanaka Y, Furukawa Y. Lab-scale characterization of CO2 absorbents
containing various amine species. Energy Proceida 2013; 37:431–435.
[3] Nakamura S, Yamanaka Y, Matsuyama T, Okuno S, Sato H. IHI’s Amine-Based CO2 Capture Technology for Coal Fired Power Plant.
Energy Proceida 2013; 37:1897–1903.
[4] Nitta M, Hirose M, Abe T, Furukawa Y, Sato H, Yamanaka Y, 13C-NMR spectroscopic study on chemical species in
piperazine−amine−CO2−H2O system before and after heating. Energy Proceida 2013; 37:869–876.