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TECHNICAL PAPERS

# Study of an Electrochemical Alcohol Concentration Sensor: Optimization of the Anode Structure

[+] Author and Article Information
Mauro Sgroi1

Microgeneration Group, Micro & Nanotechnologies, Centro Ricerche FIAT, Strada Torino 50, 10043 Orbassano, Italymauro.sgroi@crf.it

Gianluca Bollito, Gianfranco Innocenti

Microgeneration Group, Micro & Nanotechnologies, Centro Ricerche FIAT, Strada Torino 50, 10043 Orbassano, Italy

Guido Saracco, Stefania Specchia, Ugo Andrea Icardi

Materials Science and Chemical, Engineering Department, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129, Torino, Italy

1

Corresponding author.

J. Fuel Cell Sci. Technol 4(3), 345-349 (Apr 27, 2006) (5 pages) doi:10.1115/1.2756558 History: Received November 30, 2005; Revised April 27, 2006

## Abstract

Micro power sources have a wide potential market for consumer electronics and portable applications, such as weather stations, medical devices, signal units, APU (auxiliary power units), gas sensors, and security cameras. A micro power source could be the direct methanol fuel cell system (DMFC). An important aspect of this system is the precise control of the concentration of the alcohol-water solution fed to the anode. Different detection principles were taken into consideration: electrochemical, infrared spectroscopy, gas chromatography, refractometry, density measurements, ultraviolet absorption. The present work is devoted to the study of an electrochemical amperometric sensor. The device is based on the electro-oxidation of methanol to carbon dioxide on platinum catalyst into a polymeric-membrane fuel cell operated as a galvanic cell. The alcohol-water solution under examination is fed to the anode (positive side) of a polymeric membrane fuel cell, where it reacts with water to produce carbon dioxide, protons, and electrons. Protons diffuse through the electrolyte material and recombine with electrons on the cathode catalyst (negative side). At high potentials $(>0.7V)$ mass transfer of methanol to the electrode solution interface controls the observed current. Therefore, it is possible to correlate the solution concentration to the observed limiting current. This method was successfully applied to relatively diluted solutions (concentration $<1M$). The application of this principle to more concentrate solutions (up to $2M$) requires an optimization of the anode structure to enhance the influence of mass transport limitation. Moreover, during continuous operation of the sensor, a decay of the signal was observed: the absence of a steady-state current value hinders the application of the sensor. An explanation of this phenomenon and a possible solution strategy are proposed.

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## Figures

Figure 1

Scheme of the test bench for the methanol sensor testing

Figure 2

Polarization curves obtained with two sensors differing for the anode formulation. The potential scan was stopped at 0.7V with the Pt∕Ru-based sensor to avoid catalyst degradation.

Figure 3

Sensor response to different methanol concentrations. The tests were performed with a Pt-based sensor (load 1mg∕cm2) at 25°C.

Figure 4

Dependence of the sensor response from the applied electric potential. The platinum load was 1mg∕cm2, and the tests were performed at 25°C.

Figure 5

Stability of the sensor response with different applied electric potentials over long operating time. The platinum load was 1mg∕cm2, and the tests were performed at 25°C and with 1M methanol solution.

Figure 6

Dependence of the sensor response from anode platinum load. The platinum load of the cathode was 1mg∕cm2. The tests were performed at 25°C and with and applied potential of 0.8V.

Figure 7

Sensor response in the low concentration region. The platinum loads were 10mg∕cm2 for the anode and 1mg∕cm2 for the cathode. The tests were performed at 25°C and with and applied potential of 0.8V. The value of the R2 coefficient of the linear fit is 0.99.

Figure 8

Sensor response over the time span of 15 days. The variance calculated for the three data sets is 2.1%.

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