Ethanol Electrooxidation at Platinum-Rare Earth (RE = Ce, Sm, Ho, Dy) Binary Alloys

D.M.F Santos,C.A.C Sequeira,A Saccone,D Macciò,J.L Figueiredo,J.R.B Lourenço

doi:10.3390/en13071658

Abstract

Proton exchange membrane fuel cells and direct alcohol fuel cells have been extensively studied over the last three decades or so. They have emerged as potential systems to power portable applications, providing clean energy, and offering good commercial viability. Ethanol is considered one of the most interesting fuels in this field. Herein, platinum-rare earth (Pt-RE) binary alloys (RE = Ce, Sm, Ho, Dy, nominal composition 50 at.% Pt) were produced and studied as anodes for ethanol oxidation reaction (EOR) in alkaline medium. A Pt-Dy alloy with nominal composition 40 at.% Pt was also tested. Their electrocatalytic performance was evaluated by voltammetric and chronoamperometric measurements in 2 M NaOH solution with different ethanol concentrations (0.2–0.8 M) in the 25–45 °C temperature range. Several EOR kinetic parameters were determined for the Pt-RE alloys, namely the charge transfer and diffusion coefficients, and the number of exchanged electrons. Charge transfer coefficients ranging from 0.60 to 0.69 and n values as high as 0.7 were obtained for the Pt0.5Sm0.5 electrode. The EOR reaction order at the Pt-RE alloys was found to vary between 0.4 and 0.9. The Pt-RE electrodes displayed superior performance for EOR than bare Pt, with Pt0.5Sm0.5 exhibiting the highest electrocatalytic activity. The improved electrocatalytic activity in all of the evaluated Pt-RE binary alloys suggests a strategy for the solution of the existing anode issues due to the structure-sensitive EOR.

Highlights

Rising demands for energy, coupled with concerns over environmental pollution and growing fossil fuel costs, have contributed to a great need for clean and efficient power sources [1,2,3,4]
The micrographs obtained in backscattered electron (BSE) mode show for Pt0.5 Ce0.5 alloy (Figure 1a) an equiatomic PtCe grey phase and a Pt4 Ce3 bright phase at the grain borders
The voltammograms recorded between open circuit potential (OCP) and 0 V vs. saturated calomel electrode (SCE) show an anodic peak in the progressive scan and a second anodic peak in the regressive scan

Summary

Introduction

Rising demands for energy, coupled with concerns over environmental pollution and growing fossil fuel costs, have contributed to a great need for clean and efficient power sources [1,2,3,4]. The difficulty of breaking the C-C bond results in a high concentration of partial oxidation products, CH3 CHO and CH3 COOH, at the surface of platinum (Pt) catalysts, which causes a significant drop in the efficiency of the DEFC It substantially alters the environmental aspects of such a device by producing undesirable byproducts, as reported above for DMFCs. The difficulties to precisely establish the mechanism of the ethanol oxidation reaction (EOR). The authors have developed efficient Pt-RE anodes and cathodes for direct borohydride fuel cells [124,125,126] and the hydrogen evolution reaction in alkaline electrolyzers [127,128] At present, they are studying the electrocatalysis of oxygen reduction at Pt-RE alloys for application in PEMFCs. In this work, Pt-RE binary alloys, the RE elements being cerium (Ce), samarium (Sm), dysprosium (Dy), and holmium (Ho) were produced by induction heating and analyzed by SEM/EDS and XPS. The present results and conclusions are expected to provide vital kinetic data for the Pt-RE/ethanol system and to have substantial implications for new and efficient ethanol-based fuel cells

Preparation of the Pt-RE Electrodes

Catalysts Characterization

Electrochemical Measurements

Characterization of the Pt-RE Alloys

Electrochemical Properties

Conclusions