Abstract
Polymer electrolyte fuel cells with alkaline anion exchange membranes (AAEMs) have gained increasing attention because of the faster reaction kinetics associated with the alkaline environment compared to acidic media. While the development of anion exchange polymer membranes is increasing, the catalytic layer structure and composition of electrodes is of paramount importance to maximize fuel cell performance. In this work, we examine the preparation procedures for electrodes by catalyst-coated substrate to be used with a well-known commercial AAEM, Fumasep® FAA-3, and a commercial ionomer of the same nature (Fumion), both from Fumatech GmbH. The anion exchange procedure, the ionomer concentration in the catalytic layer and also the effect of membrane thickness, are investigated as they are very relevant parameters conditioning the cell behavior. The best power density was achieved upon ion exchange of the ionomer by submerging the electrodes in KCl (isopropyl alcohol/water solution) for at least one hour, two exchange steps, followed by treatment in KOH for 30 min. The optimum ionomer (Fumion) concentration was found to be close to 50 wt%, with a relatively narrow interval of functioning ionomer percentages. These results provide a practical guide for electrode preparation in AAEM-based fuel cell research.
Highlights
The attainment of efficient and affordable polymer electrolyte fuel cells (PEFCs) is fundamental to set up a hydrogen economy, claimed by the scientific community as a need to ameliorate the effects of global warming while increasing energy efficiency and reducing the emissions of pollutants
To explore the best conditions for electrode preparation, three different FAA-3 membranes were tested in the first place to select the appropriate thickness because the thickness of the membrane is a relevant aspect influencing the performance of the membrane-electrode assemblies (MEAs)
The electrodes were prepared by spraying a catalytic ink on a gas diffusion layer, and contains a certain amount of bromide counteranion that needs to be removed from the electrode before assembly
Summary
The attainment of efficient and affordable polymer electrolyte fuel cells (PEFCs) is fundamental to set up a hydrogen economy, claimed by the scientific community as a need to ameliorate the effects of global warming while increasing energy efficiency and reducing the emissions of pollutants. The core of PEFCs is the stacking of membrane-electrode assemblies (MEAs), formed by a solid polymer membrane and two electrodes (anode and cathode) These electrodes contain the catalytic layers responsible for the electrochemical reactions (hydrogen oxidation and oxygen reduction, Equations (1) and (2) for alkaline media, respectively). The interest in alkaline environments has increased enormously in recent years because the reaction kinetics for the oxygen reduction reaction (ORR) is much faster than in acidic media This is very important, because it is true for noble metal catalysts and for platinum group metal-free (PGM-free) catalysts, and the minimization or removal of PGM catalysts from the system would imply an important reduction of cost and would make it feasible to spread the fuel cell technology [5,6]. As a result of that interest, the development of novel alkaline anion exchange membranes (AAEMs) is rapidly improving the properties of alkaline MEAs [7], widening the possibilities for the design of active, robust and cost-affordable catalysts, a fact that is reflected in a large number of recent publications [8,9,10,11]
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