Abstract
Pt(Cu)/C and Pt-Ru(Cu)/C electrocatalysts with core-shell structure supported on Vulcan Carbon XC72R have been synthesized by potentiostatic deposition of Cu nanoparticles on the support, galvanic exchange with Pt and spontaneous deposition of Ru species. The duration of the electrodeposition time of the different species has been modified and the obtained electrocatalysts have been characterized using electrochemical and structural techniques. The High Resolution Transmission Electron Microscopy (HRTEM), Fast Fourier Transform (FFT) and Energy Dispersive X-ray (EDX) microanalyses allowed the determining of the effects of the electrodeposition time on the nanoparticle size and composition. The best conditions identified from Cyclic Voltammetry (CV) corresponded to onset potentials for CO and methanol oxidation on Pt-Ru(Cu)/C of 0.41 and 0.32 V vs. the Reversible Hydrogen Electrode (RHE), respectively, which were smaller by about 0.05 V than those determined for Ru-decorated commercial Pt/C. The CO oxidation peak potentials were about 0.1 V smaller when compared to commercial Pt/C and Pt-Ru/C. The positive effect of Cu was related to its electronic effect on the Pt shells and also to the generation of new active sites for CO oxidation. The synthesis conditions to obtain the best performance for CO and methanol oxidation on the core-shell Pt-Ru(Cu)/C electrocatalysts were identified. When compared to previous results in literature for methanol, ethanol and formic acid oxidation on Pt(Cu)/C catalysts, the present results suggest an additional positive effect of the deposited Ru species due to the introduction of the bifunctional mechanism for CO oxidation.
Highlights
Direct Methanol Fuel Cells (DMFCs) operating under ambient temperature are gaining interest due to their safe and profitable use as portable power in the market for mobile phones, laptops and other portable electric devices [1,2,3]
The electrochemical surface area (ECSA) for CO oxidation was determined per mol of electrodeposited Cu in order to identify the preparation conditions to obtain the most suitable core-shell nanoparticles
It was found that these normalized ECSA values were practically the same for Cu electrodeposition charges qCu in the range of 30–40 mC
Summary
Direct Methanol Fuel Cells (DMFCs) operating under ambient temperature are gaining interest due to their safe and profitable use as portable power in the market for mobile phones, laptops and other portable electric devices [1,2,3]. The attractive low temperature DMFCs possess presents certain drawbacks. The anodic electrooxidation of methanol maintains unfavorable slow kinetics, Catalysts 2016, 6, 125; doi:10.3390/catal6080125 www.mdpi.com/journal/catalysts. The methanol electrooxidation is a self-poisoning reaction because the electrogenerated CO intermediate strongly adsorbs onto the Pt surface, limiting the methanol adsorption [4,5,6,7]. CO interacts with the platinum surface in a linear, bridge and three fold configuration where each CO molecule strongly adsorbs onto one, two and three
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