New Routes for the Synthesis of Pt-Sn-Rare Earth/C Catalysts for Ethanol Oxidation Reaction
Authors: Corradini Patricia Gon , Napporn Teko W. , Kokoh Kouakou Boniface , Perez Joelma 
Published: February 2020

In the last years, direct ethanol fuel cells (DEFC) have emerged as a promising energy conversion system for portable applications. Efforts for improving the Pt electrode activity have been focused on the addition of co-catalysts able to provide external oxygen-like species at low potentials. Up to now, Pt–Sn materials seem to be the most effective catalysts for ethanol oxidation but improvements are essential for the commercialization of this technology, especially in alkaline medium [1, 2]. The rare earth oxides have a number of features that make them interesting for catalysis and also for ethanol oxidation reaction (EOR) [3-5]. The development of effective and durable electrocatalysts for alcohol electrooxidation becomes one of the goal to achieve the commercialization of DEFC. In this work, PtSn/C and PtSnEu/C were synthesized by two different routes: bromide anion exchange (BAE) method and microwave-assisted heating polyol (MWP). The trimetallic PtSnRE/C (RE: La, Ce and Pr) nanomaterials were obtained by BAE route [6]. The nanomaterials were physically characterized by inductively coupled plasma-optical emission spectrometry (ICP-OES), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results from ICP measurements revealed the presence of platinum, rare earth metal and tin in the materials obtained from both synthesis methods. No-alloy of Pt-Sn or Pt-Rare earth was observed from XRD data of materials obtained by BAE method. Probably the second added metal could be in oxides and amorphous oxy-hydroxides states. The XPS investigations permitted to confirm that tin and the rare earths were mostly in oxide form. The active area of each electrocatalyst was estimated from CO-stripping in a three-electrode cell and the current densities resulted in the EOR are higher for catalysts prepared from BAE. The in situ Fourier Transform Infrared Spectroscopy (FTIRS) technique was helpful to confirm that catalysts obtained by MWP method were less effective towards a complete ethanol oxidation. The addition of tin and rare earth in the material compositions obtained by BAE method did not change the EOR mechanism, but promoted a shift of the onset potential towards lower values. The effects of tin and rare earth were over their ability of providing oxygen species, which leads to a bifunctional mechanism. The difference in activity can probably be explained by electronic and structure changes that enhance the ethanol oxidation reaction.

Acknowledgments:

São Paulo Research Foundation (FAPESP, grant#2012/12189-8; grant#2015/13218-0) and Brazilian National Nanotechnology Laboratory (LNNano, Project XPS-20257).

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