Catalysts Based on Trimetallic Formulations for the Electro-Oxidation of Methanol
Fine metal oxide (MO2, M = Ir, Ti, etc.) nanoparticles were synthesized by a sulfite complex method. Some metal oxides are known for their good activity towards the water displacement reaction, producing surface OH species which can accelerate the oxidation of methanol intermediates. These metal oxides were subsequently mixed with a PtRu catalyst supported on carbon, prepared by the same procedure. A catalytic ink, composed of PtRu/C catalyst, MO2and Nafion ionomer, is then deposited on a carbon-cloth-based backing layer and used as composite anode in a DMFC. A commercial Pt catalyst was used at the cathode and a Nafion 117 polymeric membrane was used as electrolyte. Polarization curves at different temperatures (30-90ºC) and methanol concentrations (2-5 M) were carried out to investigate these composite anodes.
A significantly higher performance was recorded for the composite electrode-based MEAs compared to the bare one based only on PtRu/C. The results confirm that the electrocatalytic activity is related to the characteristics of water displacement prompt by the additive, which acts as a co-catalyst for this reaction. The improvement was significantly higher by using high methanol concentration in water as the fuel, which means promising utilization in DMFC systems for prolonged operation.
These results evidence that a multifunctional trimetallic catalyst can operate significantly better than PtRu for methanol oxidation since this multi-step process requires different functionalities to speed up the reaction rate. The improved electrocatalytic activity was thus attributed to the characteristics of water displacement of MO2, as occurs in the oxygen evolution process. Such a parallelism may provide new routes to design multifunctional catalysts where Pt-alloys can be combined with oxide promoters to accelerate the multiple steps of the methanol oxidation process.
The authors acknowledge the financial support from the European Community’s Seventh Framework Programme (FP7/2011-2014) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement DURAMET no. 278054.
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