Direct Electro-Oxidation of Dimethyl Ether on Pt-Cu Nanoparticles

As the use of portable devices such as mobile phones, laptops and tablets grows rapidly, efficient portable energy technologies are becoming more necessary than ever. In the past years, fuel cells made a great advancement in the field of power sources technology, and are currently referred to as the most promising alternative energy technology. The most popular type of fuel cells today is the polymer electrolyte membrane fuel cell (PEMFC), fueled with hydrogen. Although it offers very high power density, the lack of fueling infrastructure necessary for the handling of hydrogen is currently one of its biggest commercial impediments. In order to overcome this hurdle with portable devices, direct methanol fuel cells (DMFC) were proposed as an alternative. This is mainly due to the methanol's high energy density and ease of handling. DMFC's were studied thoroughly over the past decades, and the technology encountered some barriers such as slow anode kinetics, methanol crossover from the anode to the cathode and issues concerning methanol's toxicity.

Dimethyl ether (DME) is an ether gas under ambient conditions that could be liquefied under low pressure, traditionally used for aerosol propulsion and as an alternative fuel for diesel combustion engines. It was also recently suggested as an alternative fuel for low-temperature fuel cells. This is mainly due to its higher energy density when compared to methanol, 8.2 vs. 6.1 kWh kg-1. There are no C-C bonds to break in the reaction and its theoretical open cell voltage (OCV) is relatively close to DMFC, 1.18 V compared to 1.21 V at 25°C. In addition, DME has a lower dipole moment than methanol and therefore, the fuel crossover in a fuel cell is expected to be much lower than methanol's, decreasing the mixed potential impact on the cathode.

In this work, new catalyst for the direct electro-oxidation of dimethyl ether (DME) was synthesized and studied using an array of techniques. One of the most prominent catalysts for this reaction, platinum copper alloy (PtCu), was synthesized in an easy and low cost approach. Structural characterizations such as X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM) and elemental analysis revealed that the synthesized PtCu nanoparticles (3 nm on average), formed homogeneous alloy without aggregation of metallic platinum or copper. The catalyst's activity towards electro-oxidation of DME was tested using rotating disk electrode (RDE) and in membrane-electrode assembly in a full cell. The catalyst performance was found to be promising. Direct DME fuel cell (DDMEFC) studied in this work has relatively high energy density as well as low "cross-over" tendency due to a low dipole moment and thus shows great potential as fuel for low power fuel cells. The electrocatalysis of the DME oxidation reaction (DOR) was compared between synthesized PtCu and commercial PtRu/C and exhibited an enhanced performance with the newly synthesized catalyst.