(28d) Electrochemical Behavior of Pd-X/C (X=Sn, Ni, Fe) Electro-Catalysts for Ethanol Electro-Oxidation in Alkaline Media

Direct alcohol fuel cells (DAFC) has recently become in an option to generate clean and renewable energy, consist of simple systems based on electrochemical where its main components are anode, cathode, polymer membrane and alcohol. As a new technology has problems for an optimal function such as high materials prices, CO poisoning and stability. Nowadays have seen a resurgence of interest in alkaline fuel cells (AFCs) due to the development of anion exchange membranes (AEM) and the availability of non-Pt electrodes that operate under high pH conditions. However in alkaline media is very difficult to break C-C bond in spite of produce higher energy density than acid media and is easy to avoid CO poisoning.

Pd-based catalysts are promising catalysts for efficient ethanol electro-oxidation [2]. In alkaline medium ethanol has the best current density with 8030Wh/kg [3] which is a target. However there still some disadvantages, one is carbonation in the solution due to CO₂ production in the oxidation, which results in lower pH affecting the oxidation mechanism and precipitation of carbonate salts in the membrane pores. Research efforts are directed toward the design of an efficient Pd-based catalysts with high activities and stabilities have yielded. Combination between other low-cost metals such as nickel, tin and iron with palladium could improve Pd-Based catalyst performance and avoid issues explained above.

In this work, are presented results of the synthesis of Pd-Sn, Pd-Ni and Pd-Fe nano-particles supported in Carbon Vulcan XC-72, and its evaluation as an Electrode for ethanol electro-oxidation. Pd-Sn/C, Pd-Ni/C and Pd-Fe/C with 20w% of metal loading and differents molar ratios (1:1), (3:1) and (5:1). Nanoparticles were synthetized by polyol reduction using microwave heating, PdCl₂, SnCl₂.2H₂O, NiCl₂.6H₂O and FeCl₃ as metallic precursors and Carbon Vulcan XC 72R as supporting material, following the methodology described by Liu on [4]. Electro-catalytic activities were investigated via cyclic voltammetry (CV) and chronoamperometry in a three-electrode cell system at room temperature in NaOH 1M and NaOH 1M+Ethanol 2M. Glassy carbon was used as the working electrode; Platinum wire and RHE were used as counter and reference electrodes, respectively. The results showed an improvement in the performance of the electro-catalysts when palladium has the presence of other metal on surface. Also, it was determined that the molar ratio (1:1) has the best performance. As a final result, the relationship between prices and electrochemical performances was discussed.

References

[1]       N. J. Robertson, H. A. K. Iv, T. J. Clark, P. F. Mutolo, and G. W. Coates, “Tunable High Performance Cross-Linked Alkaline Anion Exchange Membranes for Fuel Cell Applications,” no. 13, pp. 3400–3404, 2010.

[2]       Z. Liu, B. Guo, L. Hong, and T. H. Lim, “Microwave heated polyol synthesis of carbon-supported PtSn nanoparticles for methanol electrooxidation,” Electrochemistry Communications, vol. 8, no. 1, pp. 83–90, Jan. 2006.

[3]       E. H. Yu, U. Krewer, and K. Scott, “Principles and Materials Aspects of Direct Alkaline Alcohol Fuel Cells,” Energies, vol. 3, no. 8, pp. 1499–1528, Aug. 2010.

[4]       Z. Liu, B. Guo, L. Hong, and T. H. Lim, “Microwave heated polyol synthesis of carbon-supported PtSn nanoparticles for methanol electrooxidation,” Electrochemistry Communications, vol. 8, no. 1, pp. 83–90, Jan. 2006.