Properties of Catalyst Layers for PEMFC Electrodes Prepared by Electrospray Deposition

Abstract

Layers composed of catalyst particles of platinum supported on carbon ͑Pt/C͒ and ionomer phase ͑Nafion͒ have been prepared by electrospray deposition. Some properties are studied, such as morphology; porosity; surface area; thermal decomposition; electroactive area; and single cell testing, relevant to their performance as catalyst layer for proton exchange membrane fuel cell ͑PEMFC͒ electrodes. A dendritic morphology is obtained by electrospray deposition, with enhanced meso-and macroporosity. Thermogravimetry analysis shows a specific interaction between Pt/C particles and the ionomer phase involving sulfonic acid groups. The electrochemical active area of Pt/C + Nafion electrosprayed films is larger, till about 30% with the optimized ionomer concentration, compared with films deposited by other common techniques or commercial electrodes. The deposited layers are studied as a cathode in single PEMFC under normalized conditions, showing improved performance due to a lower electric resistance and higher electrochemical active area. These results are explained as a consequence of the optimal mesoporous structure, improved distribution, and interaction of the ionomer film with Pt/C catalyst aggregates. The electrospray deposition may be used to prepare PEMFC catalyst layers with a reduced amount of platinum.The catalyst layer of a proton exchange membrane fuel cell ͑PEMFC͒ electrode is the part of the cell with the highest impact on cost and durability. Both issues are recognized at this moment as the major challenges for the deployment of PEMFC technology. 1,2 Within the catalyst layer, platinum nanoparticles supported on carbon black aggregates form a porous film with mesopores partially filled by a proton conducting polymer, the ionomer. The structure allows for the conduction of gas reactants and water species toward the catalyst platinum particles and the removal of excess water. One possibility for maximizing reactivity and reduce platinum requirements is the implementation of deposition methods able to properly set out the components of the catalyst layer. Appropriate porosity of the catalyst layer and ionomer distribution may increase the utilization factor of the catalyst, and at the same time, improve mass transport properties and electrical conductivity of the layer. These three properties deserve optimization to maximize the performance of the catalyst layer. The utilization factor, i.e., the ratio of the active area to total area of platinum, 3,4 for standard PEMFC electrode configurations, is typically considerably lower than 100%. A recent study by our group based on literature data and the analysis of our own data, shows that most probable platinum utilization falls in a range between 10 and 30% of the available platinum surface. 5

Ultra-low Pt loading for proton exchange membrane fuel cells by catalyst coating technique with ultrasonic spray coating machine

“…Chaparro et al [25] reported that for an electrospraying process, the optimum Pt loading (cathode) and Nafion content ratio were 0.17 mg/cm 2 and 17 wt%, respectively. The electrospray process homogeneously covered the ionomer film with the Pt/C agglomerate, forming a highly porous material with lower resistivity [26]. Sasikumar et al [29] and Martin et al [21] investigated the optimum Nafion content ratio at various Pt loadings.…”

Single Cell Study of Water Transport in PEMFCs with Electrosprayed Catalyst Layers

“…3 in Ref. ). Figure a displays the distribution obtained with N 2 adsorption, showing the micro and mesopores contributions, below 100 nm pore size, whereas Figure b displays the result from mercury porosimetry, with the meso and macropores contributions, below 100 µm pore size.…”

“…(a) Pore size distributions of electrosprayed and airbrushed layers, measured with N 2 adsorption; (b) Pores size distributions from mercury porosimetry (Data taken from ).…”

Testing of Catalyst Coated Membranes for PEMFC, Prepared by Electrospray Deposition

“…The preparation of catalyst layers of Pt/C+Nafion by means of electrospray deposition has been described in previous papers (1). Briefly, a suspension of Pt/C (E-TEK, 20 wt%) and Nafion (Aldrich, 5% solution in aliphatic alcohols) is prepared in isopropanol (Panreac).…”