Synthesis and Evaluation of PtNi Electrocatalysts for CO and Methanol Oxidation in Low Temperature Fuel Cells

Griselda Caballero-Manrique,Juan A Jaén,Pere L Cabot,Enric Brillas,Julia Garcia-Cardona,John Manuel Sánchez

doi:10.3390/catal10050563

Griselda Caballero-Manrique, Juan A Jaén + Show 4 more

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https://doi.org/10.3390/catal10050563

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Abstract

Pt(Ni)/C and PtRu(Ni)/C catalysts were synthesized by electroless deposition of Ni on a carbon dispersion followed by sequenced Pt deposition and spontaneous deposition of Ru species. The structural analyses of the catalysts with 88:12 and 98:2 Pt:Ni atomic ratios pointed out to the formation of small hexagonal Ni crystallites covered by thin cubic Pt surface structures with no evidence about PtNi alloy formation. The onset potentials for CO oxidation on Pt(Ni)/C and PtRu(Ni)/C were about 0.10 and 0.24 V more negative than those of Pt/C, thus indicating their better CO tolerance. The surface Ru species appeared to have the major effect by facilitating the CO removal by the bifunctional mechanism. The onset potential for the methanol oxidation reaction (MOR) of Pt(Ni)/C was about 0.15 V lower than that of Pt/C. The mass and specific activities together with the exchange current densities of the Pt(Ni)/C catalysts were also higher than those of Pt/C, making in evidence their higher activity in front of the MOR. The Tafel slopes for the MOR on Pt(Ni)/C suggested different reaction mechanism than on Pt/C. The electronic (ligand) effect of Ni on Pt was considered the main reason to explain the higher activity of Pt(Ni)/C in front of the CO oxidation and the MOR.

Highlights

The shortage of fossil fuel deposits increases over time along with the energy demand, causing a negative impact on the environment
These values were greater for Pt(IV):Ni(II) ratios of 3:1 and 8:1. This can be explained by the different number of Pt active sites in each specimen, which were smaller in the case of 1:1 and 2:1 due to an insufficient amount of Pt to effectively cover the Ni cores
The X-ray diffraction (XRD), HRTEM and Fast Fourier Transform (FFT) analyses pointed out to the formation of small hexagonal Ni crystallites covered by cubic Pt surface structures with no evidence about PtNi alloy formation

Summary

Introduction

The shortage of fossil fuel deposits increases over time along with the energy demand, causing a negative impact on the environment. Many researchers worldwide have turned their attention toward a common goal of developing alternative energy sources. Fuel cells have emerged as an alternative to other energy sources. A fuel cell is an electrochemical device that converts directly the chemical energy of a reaction into electrical energy. It allows electricity to be generated by two electrodes, an anode and a cathode, separated by an electrolyte, combining hydrogen and oxygen electrochemically, in the absence of combustion reactions [2]. Very high efficiencies can be reached because they are not affected by Carnot’s heat engine limitation and the absence of moving components within the device, reducing the friction losses that are present in an internal combustion engine

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