Preparation Of Pemfc Catalyst Electrode Using Ion-exchange Electroreduction Method

Proton exchange membrane fuel cell (PEMFC) is one of the most promising cells used for automotive, small power stations and mobile power supplies for prominent merits, such as high energy density, low operating temperature, cleaning and well stability. However, the key issues of life, cost, performance and other technical problems have hindered PEMFC commercialization. Therefore, reduction of Pt catalyst loading and increase of Pt catalyst utilization have been becoming two important topics for decades.Traditional PEMFC catalyst layer was usually prepared by coating or printing a mixture of Pt/C catalyst powder with Nafion solution and solvent. Most of the catalysts could not get protons, electrons and O₂ and then were wasted. It causes the reduction of catalyt utilization. To solve this problem, the present art proposed an ion-exchange/electroreduction approach to deposit Pt selectively on the three-phase interface of carbon and proton exchange membrane, so as to improve the catalyst utilization and reduce Pt loading.At first,the gas porous electrode was prepared, which had electronic access, gas channel and the proton channel; and then,Pt cations was exchanged and adsorbed onto Nafion through ion-exchanging; applying a reduction current to electrode, for carbon can transmit electrons, Pt was deposited on three-phase interface of carbon and proton exchange membrane. The Pt grain size, shape and dispersion could be effectively controlled by adjusting the concentration of Pt(NH₃)₄Cl₂, Nafion content and the times of ion-exchange electroreduction.The influence of the concentration of Pt(NH₃)₄Cl₂ solution, Nafion content and the times of ion-exchange/electroreduction on the Pt grain size, dispersion and particle distribution was studied by scanning electron microscope (SEM). The catalytic activity and catalytic efficiency of Pt /C catalyst were assessed by cyclic voltammetry (CV) and linear sweep (LSV).The results of single cell test show that the Pt /C catalyst electrodes have high utilization. The membrane electrode assemblies employing ion-exchange/electroreduction electrode with a Pt loading of 0.014 mg.cm^-2 on the anode and 0.3 mg cm^-2 (Johnson-Matthey 40% Pt/C) on the cathode output power of 0.7 W.cm-2. It is a remarkable improvement for a PEMFC that can output such a great power with such a low Pt loading of 0.014 mg.cm^-2.