Polydopamine for the Design of Corrosion-Tolerant Polymer Electrolyte Membrane Fuel Cell Electrodes

Abstract

For application in mobile power supply systems, polymer electrolyte membrane fuel cells (PEMFC) are promising candidates due to their high efficiency and low emission. In principle, the fuel cell technology is long ready for its commercial market launch, hindered by its high cost, mainly caused by the price of the electrode catalyst which consisted mostly of noble metal platinum unsupported or supported on carbon support. An other major constraint is the limited long term stability of the catalyst support itself subjected to the severe conditions of the fuel cell environment. Indeed, standard carbon supports tend to corrode in environments of high water content, acidic pH, elevated temperatures (50-90°C), high potential (0.6-1.2 V), and high oxygen content. Moreover, the presence of platinum also accelerates the carbon corrosion. Hence, nowadays it is more and more important to develop new solutions to improve the PEMFC tolerance to corrosion. In the present work, our team worked on improving the PEMFC performance parameters, which include enhanced power density, increased catalyst utilization and reduce cost with the incorporation of alternative materials like Multi-Walled Carbon Nanotubes (MWCNTs) in combination with polydopamine (PDA) into electrodes architecture. The role of MWCNTs was to confer a high electronic conductivity and help to form a porous network. On the other side the role of PDA was to promote the proton conductivity similarly to ionomers such as Nafion. The fuel cell polarization test shows a maximum power density of 780 mW.cm−2 and a Pt utilization of 6051 mW.mg(Pt)−1. The Pt utilization reached in this work is almost three times higher than for Pt/MWCNTs electrodes containing the same Pt loading. In this study, fuel cell membrane were prepared applying sprayed layer-by-layer assembly deposition method from polydopamine (PDA) and multi-walled carbon nanotubes (MWCNTs). Pt nanoparticles were attached to the MWCNTs in a reaction of selective heterogeneous nucleation. MWCNTs were coated with mussel-inspired PDA. After functionalization, Nafion perfluorinated resin solution was add to the suspension to obtain a stable dispersed solution for LBL assembly. The MEAs were sandwiching by two pieces gas diffusion layer and fed with H2/O2. The originality of this work was to prove that PDA acts as a fantastic protective layer against carbon corrosion. To this aim, we performed cyclic voltammetry measurments (CV) on both MWCNTs and PDA-MWCNTs systems in order to simulate harsh conditions occuring in a PEMFC electrodes in acidic environment. Transmission Electron Microscopy (TEM) obersations were also realized showing a partial covering of MWCNTs by PDA, estimated at 20% using a X-ray Photoelectron Spectroscopy (XPS) theoritical model. Nethertheless, a such covering leads to significative resistance to corrosion in the range of potential and number of cycles studied. This study showed a simple preparation technique for high performance and long lasting advanced electrode structures which succeeded in incorporating PDA into a porous MWCNTs network. As far as we know this is the first time that Pt/MWCNTs-PDA is used in a real PEMFC environment. PDA-MWCNTs supports exhibit a better oxidation resistance than MWCNTs. This work opens the way to the manufacturing of efficient, stable and easily prepared PEMFC electrodes.