Highly active dimethyl ether anode catalysts for advanced low temperature fuel cells

Dimethyl ether (DME) was recently proposed as an alternative fuel for fuel cells, due to its high energy density (8 kWh kg⁻¹), low boiling point (-24 °C) thus it can be introduced as gas to the cell, and its low crossover rate through the Nafion® membranes allowing the use of thin membranes. Yet, the state-of-the-art DME oxidation catalysts, such as PtRu, have slow oxidation kinetics and limited durability. Fuel cells utilizing Pt based catalysts require high anode loading (above 2-4 mg of Pt), pressure and temperature which are relatively high (1.4 - 3.0 bar and 80 ֯C) to produce power output of 60- 200 mW/cm².

We present a study of our patented ternary PtPdSn\C catalyst. Comparison with Pt\C, Pd\C, and PtPd\C catalysts was made to explore the role of the different metals in the oxidation process over PtPdSn. High electrto-activity towards DME oxidation was maintained even after prolonged cycling in 0.5 M H₂SO₄ saturated solution. Polymer electrolyte fuel cell (PEMFC) implementing PtPdSn/C catalyst produces peak power density of 210 mW/cm² with loading of only 1.6 mg/cm² of platinum group metals (PGM) at 70 ֯C and ambient pressure, significantly higher than any reported power density. Mechanistic analytical analysis of the DME oxidation products by online mass spectrometry and online FTIR showed formic acid as the main partial oxidation product at water stichometry lower than 3, whereas at full hydration, above 3 moles of water per mole of DME, the main product other than CO₂ was methanol resulting from hydrolysis reaction of the ether bond. The results mentioned above suggest that DME fed directly to PEMFC has good potential of becoming a viable alternative to compressed hydrogen fueled fuel cells.