The Application of Ultrasound to the Coating of Platinum Catalyst on Membrane for Proton Exchange Membrane Fuel Cell

MEA (Membrane Electrode Assembly) consisting of the electrodes coated with a catalyst and the membrane is the most important in fuel cell. In fabricating MEA, there are two ways to coat catalyst depending on a coating substrate, i.e. CCM (Catalyst Coated Membrane, coating on membrane), and CCS (Catalyst Coated Substrate, coating on carbon paper). Generally, CCM is known as a better way than CCS, and spray coating has been widely used for CCM method. In this study, CCM method was also adopted to make MEA, however, catalyst was coated sonochemically to introduce a new catalyst coating method in making MEA.

The most convincing and famous mechanism known for a sonochemical metal ion reduction is a reduction of metal precursor by radicals generated by hot spot during ultrasound irradiation¹. Thus we introduced ultrasound irradiation for synthesizing and coating of platinum on membrane simultaneously. In applying ultrasound irradiation, we changed experimental conditions such as time of radiation and the intensity of radiation. The amount of platinum loaded on membrane was proportion to the time and the power of ultrasound irradiation as shown in Fig. 1. The solution used for platinum electrode formation includes not only platinum precursor but also a reducing agent and a surfactant to help precursor reduction. After Pt catalyst coating, remaining impurities like a reducing agent and a surfactant were removed by using stirring in pure water.

In order to check whether platinum was successfully loaded on membrane, FE-SEM (Field Emission Scanning Electron Microscope) and EDS (Energy Dispersive x-ray Spectroscopy) analyses were carried out as shown in Fig. 2, and it proved the effectiveness of ultrasound irradiation in making platinum electrode on membrane. Furthermore, we looked into the electrochemical characteristics of the MEA using CV (Cyclic Voltammertry) and EIS (Electrochemical Impedance Spectroscopy), and then the  result was compared with that of a conventional MEA. MEAs, both new and conventional, were made into single cells for a performance test and a comparison. In making a single cell with the MEA made by ultrasound irradiation, ionomer effect was thoroughly studied to take advantage of thin thickness of platinum catalyst layer. It is known that the mass transfer through thin film catalyst layer is fast without ionomer².

In thus presentation, all the results investigated in the study will be presented with in-depth discussion.

References:

1. J. H. Bang and K. S. Suslick, Adv. Mater., 22, 1039 (2010).

2. A. K. Schmoeckel, G. D. Vernstrom, R. Atanasoski, and M. K. Debe, J. Power Sources, 161, 1002 (2006).