Performance Tests of Poly(vinyl alcohol)-Based Membranes for Alkaline Direct Ethanol Fuel Cells

Abstract

Alkaline direct ethanol fuel cells (ADEFCs) are capable of converting ethanol, a CO2 neutral fuel, into electrical energy, which is why interest in this technology has been growing rapidly in recent decades. An important component, as it contributes significantly to the efficiency and performance of these fuel cells, is the anion exchange membrane (AEM). Nowadays, commercially available polymer AEMs have limiting properties for application in fuel cells: low thermal, chemical and mechanical stability and conductivity, moreover they are not environmentally friendly and expensive. Therefore, it is important to ensure the following properties for AEMs for optimal fuel cell operation: high hydroxide ion conductivity, low ethanol permeability, no electron conduction, and high thermal and chemical stability. In this study, Poly(vinyl alcohol) (PVA), a low cost polyhydroxy polymer was tested as main-backbone for the membrane because of its promising properties: it is hydrophilic, has low ethanol permeability, is non-toxic and crosslinking susceptible. Glutaraldehyde (GA)-based crosslinked (improvement of chemical stability of the membrane and reduction of membrane swelling) AEMs with PVA as backbone polymer were prepared and the performance of the membrane was examined in an ADEFC and compared to a commercial FAA-3 fumasep® membrane [1].The following preparations were made before performing the single cell test. Both membranes (the self-made PVA-based and the commercial FAA-3 fumasep® membrane) were pretreated by immersing them in 1 M KOH for 24h followed by excessive washing with ultrapure water. The PdNiBi/C anode catalyst [2] and the commercial PtRu/C cathode catalyst inks were deposited using an automatic ultrasonic spray coater on the gas diffusion layers (GDLs): carbon cloth and carbon paper, respectively. A metal loading of 0.75 mg cm-2 for the ethanol oxidation reaction and 0.5 mg cm-2 for the oxygen reduction reaction on the electrodes was achieved. The electrodes and the membrane were sandwiched together to prepare the membrane electrode assembly, which was inserted into the fuel cell. A mixture of 1 M KOH and 1 M EtOH with a flow rate of 5 mL min-1 served as anode fuel and oxygen gas with a flow rate of 25 mL min-1 as cathode feed gas. Different operational temperatures were used for the measurements: RT, 36°C, 44°C, 53°C, 57°C. A Gamry Reference 600TM Potentiostat was used to determine the current densities (I) and cell potentials (V) to plot the typical I-V and I-P curves.The I-V (left axis, open symbols) and I-P (right axis, filled symbols) plots as well as the temperature dependency of the maximum power density of the PVA-based membrane can be seen in Figure 1. The maximum power density increases with temperature because of the better reaction kinetics and higher conductivity. The best performance was achieved at an operation temperature of 57°C: 8.6 mW cm-2 at a current density of 47.6 mA cm-2. The commercial membrane in comparison at the same measurement conditions showed only 5.4 mW cm-2 at a current density of 27.0 mA cm-2. The higher maximum power density of the GA crosslinked PVA-based membrane can be linked to the better conductivity of the membrane.The results from the single cell tests of the prepared PVA-based membrane compared to the commercial membrane indicate that PVA-based membranes can be applied for future membranes in ADEFCs. Further details and results will be discussed in the presentation.The authors acknowledge the financial support by the Austrian Science Fund (FWF I 3871-N37).[1] A. M. Samsudin, S. Wolf, M. Roschger, V. Hacker, International Journal of Renewable Energy Development, 2021, 10(3), 435-443.[2] B. Cermenek, B. Genorio, T. Winter, S. Wolf, J. G. Connell, M. Roschger, I. Letofsky-Papst, N. Kienzl, B. Bitschnau, V. Hacker, Electrocatalysis, 2020, 11, 203-214. Figure 1