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Fe/N/C catalysts with high activity for oxygen reduction in acid medium
Nadirov R. , Sabirov Ye. (Republic of Kazakhstan)
Катализатор Fe/N/C с высокой активностью для восстановления кислорода в кислой
среде
Надиров Р. К. , Сабиров Е. (Республика Казахстан)
1 Надиров Рашид Казимович /Nadirov Rashid - кандидат химических наук, доцент;
2'Сабиров Ерлан / Sabirov Yerlan - магистрант, факультет химии и химической технологии,
Казахский национальный университет им. аль-Фараби, г. Алматы, Республика Казахстан
Аннотация: в статье обсуждается возможность получения катализаторов Fe/N/C для реакции восстановления кислорода. Синтезирован катализатор Fe/N/C на основе м-фенилендиамина.
Abstract: the possibility of obtaining Fe/N/C catalysts for oxygen reduction reaction is discussed in this paper. The Fe/N/C catalyst on the base of m-phenylendiamine is synthesized.
Ключевые слова: катализатор Fe/N/C, восстановление кислорода, синтез Keywords: Fe/N/C catalyst, oxygen reduction, synthesis
Polymer electrolyte membrane fuel cells (PEMF) are environmental friendly power generators for different applications. Because of their low-temperature operation, catalysts are needed at both anode and cathode to improve the kinetics of the electrochemical reactions and thus produce useful currents at these electrodes. Mostly, precious metals remain the best catalysts material for PEMF [1]. However, there is a strong incentive to find alternative catalysts to precious metals due to scarcity and expensivity. Non-precious catalysts based on Fe ions are among the possible alternatives [2, 3].
The N550 carbon black was grafted with sulfophenyl group through reduction of diazonium salt. The sulfophenyl diazonium salt was synthesized through 4-aminobenzenesulfonic acid, NaNO2, and 1 M HCl in 5 °C cooling bath. The obtained diazonium salt and reduced Fe powder were poured into the carbon black suspension. The reaction mixture was stirred overnight to graft sulfophenyl group onto carbon surface. The suspension was mixed with m-phenylendiamine and concentrated HCl. To this suspension, pre-cooled (NH4)2S2O8 and FeCl3 solution were added. The suspension was filtered and water washed. The dry powder was mixed with FeCl3 solution and 100 mL water. Then, the solvent was removed through rotary evaporator and further dried in oven for 8 h at 80 °C. The resulting powder was subjected to the heat treatment at 700-900 °C in nitrogen atmosphere for 1 h. The pyrolyzed sample was then acid leached in 1 M HNO3 solution at 80 °C for 8 h followed by centrifugation and washing with distilled water.
For ORR performance, 10.0 mg of catalyst sample was dispersed in 0.5 mL water, 0.5 mL ethanol, and 50 pL 5 wt % Nafion solution for 1 hour to form a uniform catalyst ink. Then, 25 pL of the ink was dropped onto the glass-carbon disk. The electrolyte was 0.1 M H2SO4 and was bubbled with air. The electrode was subjected to potential cycling between 1.0 to 0.2 V (RHE) at a scan rate of 10 mV s-1.
As mentioned above, the purpose of this work was to obtain a catalyst that is active toward the following electrochemical reduction reaction of oxygen (ORR):
O2 + 4H+ + 4e = 2H2O
The activity of catalyst toward ORR, usually expressed as a value of current made at a specific value of the potential (0.7 - 0.9V) per unit weight of catalyst (g), or unit of catalyst surface (cm2). Currently, commercial Pt-containing catalysts are of the order of 100-230 A/g platinum at 0.9 A and 1000-1500/g platinum at 0.85 V. In terms of the specific surface of the catalyst, these values are about 200-300 mA/cm2 (at 0.9) and 400-500 mA/cm2 (at 0.8 V). The spread of the values associated with different dispersion of platinum in the catalyst (the higher the dispersion, the higher ceteris paribus indicators of activity).
Figure 1 shows the polarization curves obtained at positive potential scanning of catalysts after the heat treatment while blowing air, in 0.1 M H2SO4.
It can be seen that catalyst prepared by pyrolysis at 900 0C shows the largest activity toward ORR. This catalyst is characterized by the value of the current density 280mA/cm2 at 0.8 V and 90 mA/cm2 at 0.9 V.
1
-5 J
Potential, V
3
Pyrolysis temperature, 0С: 1 - 900; 2- 1000; 3- 700 Scan rate: 10 mV/s
Fig. 1. ORR polarization curves, obtained in 0,1 МH2SO4 References
1. Peighambardoust S. J., Rowshanzamir S., Amjadi M. Review of the proton exchange membranes for fuel cell applications. // International Journal of Hydrogen Energy. - 2010. - Т. 35. - №. 17. - С. 9349-9384.
2. Yuan X. Z., Li H., Zhang S., Martin J., Wang H. A review of polymer electrolyte membrane fuel cell durability test protocols. // Journal of Power Sources. - 2011. - Т. 196. - №. 22. - С. 9107-9116.
3. Othman R., Dicks A. L., Zhu Z. Non precious metal catalysts for the PEM fuel cell cathode. // International journal of hydrogen energy. - 2012. - Т. 37. - №. 1. - С. 357-372.
