Graphene Derivatives As Carbon Support Material in Alkaline Direct Ethanol Fuel Cells

Abstract

The increasing global demand for energy and the associated rise in CO2 emissions due to the use of fossil fuels require the development and use of renewable energy sources. In this context, fuel cells are identified as one of the key technologies for clean energy production. Nevertheless, there are three critical technical barriers for fuel cells that limit their commercialization: performance (activity), durability (stability) and cost. Alkaline fuel cells, particularly alkaline direct ethanol fuel cells (ADEFCs), have attracted much attention in recent decades because ethanol fuel is easy to handle, store, and transport, has low cost, and is environmentally friendly.ADEFCs are limited by their slow kinetics, especially the electrochemical reaction at the anode. Currently, no catalyst is available that cleaves the carbon-carbon bond of ethanol, resulting in a CO2 efficiency of 100% (C1 pathway). The ethanol oxidation reaction (EOR) in alkaline media is incomplete and predominantly follows the C2 pathway. Ethanol is oxidized by hydroxide ions to acetate as the main oxidation product and 4e- instead of 12e-, CO2 and water are released during the complete oxidation. During EOR, acetate is adsorbed on the catalyst surface as the active species. Nevertheless, various reaction intermediates deactivate the catalyst due to poisoning of the active sites, thus reducing the EOR performance. Palladium is currently the most suitable catalyst to replace platinum in ADEFCs. Palladium precursor salts are also cheaper than platinum salts and Pd/C catalysts show higher EOR activity (ethanol oxidation reaction) than Pt/C under alkaline conditions. This can be attributed to the higher oxophilic properties and the inherent ability of Pd to cleave C-C bonds. This positive effect also results in higher stability and lower susceptibility to poisoning of the active sites of the Pd catalyst during EOR. In addition, many non-precious metal co-catalysts are available for palladium, which further reduce the material cost while improving the catalytic activity, by-product tolerance and stability for alkaline EOR [1,2].The development of new anode catalysts with high activity and stability towards alkaline EOR is essential to improve the performance of direct ethanol fuel cell. Carbon materials, especially N-doped or reduced graphene oxides (rGO), are a promising catalyst support due to their low cost, high electrical conductivity, large surface area, and reasonable stability [3]. The deposition of the metal nanoparticles on the graphene oxide support generates a higher active surface area of the catalysts, which increases the electrocatalytic activity while reducing the cost.In the current studies, palladium-based catalysts are synthesized with different graphene oxide (GO) support materials (N-doped GO and rGO) by the modified instant method. The prepared catalysts were characterized ex-situ by the thin film rotating disk electrode technique using a standard three-electrode setup. To determine the electrochemical active surface area and EOR activity, cyclic voltammetry and EOR measurements were recorded in N2 purged potassium hydroxide and alkaline ethanol solution (1 M), respectively. Chronoamperometry was performed to investigate the stability of the catalysts. The cyclic voltammograms (CV) of the two catalysts compared show minor differences in peak current density, onset potential and by-product tolerance for the alkaline EOR. Further details will be discussed in the poster presentation.The authors acknowledge the financial support by the Austrian Science Fund (FWF): I 3871-N37 and by the Slovenian Research Agency (ARRS) through the Research Funding Programme P1-0175 and Bilateral Research Funding Project N2-0087.[1] B.Cermenek, J.Ranninger, V.Hacker; In Ethanol: Science and Engineering, A.Basile, A.Iulianelli, F.Dalena, N.T.Veziroglu, Eds.; Elsevier Inc.: Amsterdam, 2019, 383-405.[2] B.Cermenek, J.Ranninger, B.Feketeföldi, I.Letofsky-Papst, N.Kienzl, B. Bitschnau, V. Hacker, Nano Research, 2019, 12 (3), 683-693.[3] M. Nosan, M. Löffler, I. Jerman, M. Kolar, I. Katsounaros, and B. Genorio, ACS Appl. Energy Mater. 2021 Figure 1