Fuel cells have attracted great attention in recent times as a promising replacement for traditional engines. They offer numerous benefits such a high power density, compactness, lightweight and zero or low greenhouse emissions. There are different types of fuel cells, which transform the energy of a chemical reaction directly into electrical energy. One of the most attractive and effective, particularly, in terms of transportation applications are Proton Exchange Membrane Fuel Cells (PEMFC).

The Membrane Electrode Assembly (MEA) is the most important part of a fuel cell. The MEA is composed of two electrodes (anode and cathode), and a polymer exchange membrane. Each electrode is composed of different layers, the gas diffusion layer (GDL), Micro Porous Layer (MPL) and the catalyst layer (CL). MPL is important due to its role in efficient electron transfer process and effective transport of reactants towards the catalyst layer and removal of products from the MEA. The MPL also serves an electrical contact link between the carbon paper and the catalyst layer. Hence enhancing electrical contact by using highly conductive materials is expected to reflect in improved performance.

Great efforts have been made to research of different materials which have good electron conductivity to improve the reaction kinetics, as they facilitate easier travel of electrons in the electron pathway, thereby increasing the performance.

Graphene oxide (GO) is considered as a good proton conducting material, at the same time it is impermeable to dry gases and electrons. N-doped graphene has even used as an efficient electrode material in a variety of applications such as catalyst for oxygen reduction reactions in PEMFC, lithium-ion batteries and supercapacitors [1]. Because of their properties, GO and N-doped graphene can be considered as good candidate materials to use in a MPL.

Several graphene preparation methods have been developed, such as chemical vapour deposition (CVD), arc discharge, segregation growth or Hummers method. However, the requirements of expensive equipment used, extreme reaction conditions and the usage of highly toxic chemicals are some of the inconvenient that these techniques present. Electrochemical exfoliation of graphite has been presented as a green and cost-effective approach for producing high quality of graphene in high yield using simple equipment [1-3].

In this work, GO and N-doped graphene have been prepared by electrochemical exfoliation of graphite in aqueous inorganic salt and ammonium nitrate as electrolyte. This process is performed in a two electrode system using platinum as the counter electrode and graphite sheet as a working electrode under neutral pH conditions. A power supply is used to apply a voltage of 10V. Different MEAs are been assembled using the GO and N-doped graphene in the MPL. The enhanced performance of these MEA’s in different fuel cell such as DMFC, Hydrogen Fuel Cell (PEMFC) and Direct Formic Acid Fuel Cell (DFAFC) will be described.

We have shown that the replacement of the carbon material used in the MPL by reduced graphene oxide (rGO) and (GO) on the cathode side can provide significant improvement on the power density of up to 84%.

References:

[1] Richard Gondosiswanto, Xunyu Lu, and Chuan Zhao. Preparation of Metal-Free Nitrogen-Doped Graphene via direct electrochemical exfoliation of graphite in ammonium nitrate. Australian Journal of Chemistry, 68 (2015) 830-835.

[2] Xunyu Lu and Zhao. Controlled electrochemical intercalation, exfoliation and in-situ nitrogen doping of graphite in nitrate-based proton ionic liquids. Physical Chemistry Chemical Physics,15 (2013), 30005-200009.

[3] Khaled Parvez, Ahong-shuai Wu, Tongjin Li, Xianjie Liu, Robert Graft, Xinliang Feng, and Klaus Mullen. Exfoliation of Graphite into Graphene in Aqueous solution of Inorganic Salts. Journal of the American Chemical Society, 136, (2014), 6038-6091.