2, Centro de Investigacion y Desarrollo Tecnologico en Electroquimica, Queretaro, Queretaro, Mexico
Energy sources for all kind of electronic devices are under constant pressure to achieve higher efficiency levels by increasing the energy density and decreasing both volume and weigh while reducing the cost of portable power sources at the same time . Mixed-reactant microfluidic direct methanol fuel cells (MR-μDMFCs) represent a promising power supply alternative for electronic portable devices in the future, due to their simplicity of design, fabrication and operation. Theoretically, they can achieve higher energy density in comparison with other DMFCs. The main challenge arises from the need for selective electrocatalysts . The synthesis of cathode materials with high mass specific activity towards the oxygen reduction reaction (ORR) and no activity towards the methanol oxidation reaction (MOR) is crucial for the development and commercialization of MR-μDMFC.
In the present work, we report a two-step synthesis by pulsed laser deposition (PLD) of two Pt-based catalysts having a layer onto layer structure. For the two catalysts, first an ultra-low loading Pt layer is deposited directly on carbon nanotubes and further coated with a porous Ag layer or a porous Mn2O3 layer, obtaining Ag/Pt/CNTs and Mn2O3/Pt/CNTs, respectively. According to the physicochemical characterization, these layers don’t present electronic interaction with each other. The resulting binary materials exhibit electrocatalytic activity similar to Pt towards the ORR in alkaline media. The RRDE studies reveal that the ORR on both Pt/CNTs and Mn2O3/Pt/CNTs, is carried out through a 3.9 electron transfer mechanism, while on Ag/Pt/CNTs, the transfer is about 3.7 electron. Interestingly, the bilayer cathodes show no activity for the MOR. Furthermore, those materials demonstrate to be tolerant to methanol concentration as high as 5 M. The results suggest that the superficial Ag and Mn2O3 components discriminate between the molecular volume of O2 and MeOH. Lastly, in order to compare the performance of the methanol-tolerant cathodes in a fuel cell, the materials are tested in a passive, air-breathing MR-μDMFC in conditions close to real application.
 E. Kjeang, Microfluidic fuel cells and batteries, Springer, 2014
 R. O'hayre, S.-W. Cha, F.B. Prinz, W. Colella, Fuel cell fundamentals, John Wiley & Sons, 2016.