Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are considered to have potential as clean energy converters for future applications. There are huge cost considerations due to the usage of noble metal Pt which hinders its commercialization. To reduce the amount of Pt loading, Carbon with Pt nanoparticles is used but under harsh conditions in the PEMFC electrode, carbon materials and nanotubes degrade.
Researchers led by Dr. Marc Michel at Luxembourg Institute of Science and Technology used electrode structure made up of polydopamine (PDA) and carbon nanotubes in PEMFCs to enable the electrode to withstand the operating conditions arising in the fuel cell. The study is now published in Journal of Power Sources.
Polydopamine, among other advantages, is quite beneficial due to the presence of catechol and amino groups which leads to strong binding between PDA and Pt precursor. It promotes the conductivity of protons. Carbon nanotubes enhance the contact between the catalyst and the electrolyte as they form interconnected conducting networks. Thus, a structure having carbon nanotubes with Pt nanoparticles and coated with polydopamine was chosen for the research. This structure would save the carbon material from oxidation which occurs under the extreme operating conditions of the system.
The scientists prepared a new electrocatalytic active (Pt/MWNTs-PDA)50 multi layered nanocomposite film with spray deposition which is much faster (100 times) than the conventional layer by layer (LBL) assembly. Two catalysts supports were prepared, one having multiwalled carbon nanotubes with Pt nanoparticles but without polydopamine as a reference, and the other wrapped with PDA. Physical characterisations were carried out using various methods (XPS, SEM, etc.) to realize the specifications for the experiment. The results yielded by the characterization showed the PDA covering of 19 %.
In their adsorption/desorption study of the catalyst in hydrogen and oxygen it was observed that the coating of PDA to the catalyst doesn’t affect the catalytic reactions. By Cyclic Voltammetry, the Electrochemical Charged Surface Area (ECSA) for Pt/MWNTs-PDA was found to be 15.2 m2/g(Pt) and for Pt/MWNTs was 10.3m2/g(Pt) for the first cycle. In subsequent cycles, the ECSA for the former was stable and degraded for the latter.
The polarization curves obtained show that the Pt/MWNTs-PDA has a lower open circuit voltage (OCV) than Pt/MWNTs. It is believed by the scientist that OCV will further decrease if PDA content is increased but it is yet to be experimentally confirmed. The concentration losses, on the other hand, shown by Pt/MWNTs-PDA are at higher current densities than that of Pt/MWNTs where the concentration losses start at an earlier current density of 1200 mA/cm2. The concentration loss zones of the former are observed to be unstable at high current densities. The scientists infer that the instability might be due to some change in cathode structure.
The stability of the two catalyst supports were compared by continued cyclic voltammogram test. The conductivity of PDA-MWNTs was shown to be stable even after many cycles of operation as the surface resistance did not change. Also, the integral area of cyclic voltammograms for PDA-MWNTs did not change implying a good electrochemical stability. It was also observed, with the normalized plots, that the MWNTs would tend to corrode, and in comparison, PDA-MWNTs do not tend to corrode easily as they have the ability to decrease the overpotential of oxidation.
The research team was able to show that PDA-MWNTs are resistant to oxidation, and show a higher Pt Utilization of 6051 mW/mg which is three times as high as utilization obtained by MWNTs of the same Pt loading. PDA-MWNTs also show better performance based on the power densities observed. For the first time, they showed that polydopamine protects the electrode from corrosion of carbon.
To learn more about the research (EnergyCell)
Hongtao Long3, Doriane Del Frari3, Arnaud Martin3, Joffrey Didierjean3, Vincent Ball1,2, Marc Michel3, Hicham Ibn El Ahrach3. Polydopamine as a promising candidate for the design of high performance and corrosion-tolerant polymer electrolyte fuel cell electrodes. Journal of Power Sources, pp. 569-577, 2016.Show Affiliations
1 Unité INSERM 1121, Faculté de médecine, 11 rue Humann, 67085 Strasbourg Cedex, France
2 Université de Strasbourg, Faculté de Chirurgie Dentaire, 8 rue Sainte Elisabeth, 67000 Strasbourg, France
3 Luxembourg Institute of Science and Technology (LIST), Materials and Research Technology (MRT), 5 Avenue des Hauts-Fourneaux, L-4362 Esch/Alzette, Luxembourg
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