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4 results on '"Pieter B. J. Levecque"'

1. Formation of Pt-Based Alloy Nanoparticles Assisted by Molybdenum Hexacarbonyl

Author

Gerard M. Leteba, David R. G. Mitchell, Pieter B. J. Levecque, Eric van Steen, and Candace I. Lang

Subjects
alloys, nanoparticle, molybdenum hexacarbonyl, surfactants, STEM-EDXS, thermolytic synthesis, Chemistry, QD1-999
Abstract

We report on an optimized, scalable solution-phase synthetic procedure for the fabrication of fine-tuned monodisperse nanostructures (Pt(NiCo), PtNi and PtCo). The influence of different solute metal precursors and surfactants on the morphological evolution of homogeneous alloy nanoparticles (NPs) has been investigated. Molybdenum hexacarbonyl (Mo(CO)6) was used as the reductant. We demonstrate that this solution-based strategy results in uniform-sized NPs, the morphology of which can be manipulated by appropriate selection of surfactants and solute metal precursors. Co-surfactants (oleylamine, OAm, and hexadecylamine, HDA) enabled the development of a variety of high-index faceted NP morphologies with varying degrees of curvatures while pure OAm selectively produced octahedral NP morphologies. This Mo(CO)6-based synthetic protocol offers new avenues for the fabrication of multi-structured alloy NPs as high-performance electrocatalysts.

Published
2021
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2. Solution-Grown Dendritic Pt-Based Ternary Nanostructures for Enhanced Oxygen Reduction Reaction Functionality

Author

Gerard M. Leteba, David R. G. Mitchell, Pieter B. J. Levecque, and Candace I. Lang

Subjects
thermal decomposition, ternary alloy, nanodendrites, surfactants, oxygen reduction reaction, electrocatalysts, Chemistry, QD1-999
Abstract

Nanoalloys with anisotropic morphologies of branched and porous internal structures show great promise in many applications as high performance materials. Reported synthetic approaches for branched alloy nanostructures are, however, limited by the synthesis using a seed-growth process. Here, we demonstrate a conveniently fast and one-pot solution-phase thermal reduction strategy yielding nanoalloys of Pt with various solute feed ratios, exhibiting hyperbranched morphologies and good dispersity. When Pt was alloyed with transition metals (Ni, Co, Fe), we observed well-defined dendritic nanostructures in PtNi, PtCo and Pt(NiCo), but not in PtFe, Pt(FeNi) or Pt(FeCo) due to the steric hindrance of the trivalent Fe(acac)3 precursor used during synthesis. In the case of Pt-based nanoalloys containing Ni and Co, the dendritic morphological evolution observed was insensitive to large variations in solute concentration. The functionality of these nanoalloys towards the oxygen reduction reaction (ORR); however, was observed to be dependent on the composition, increasing with increasing solute content. Pt3(NiCo)2 exhibited superior catalytic activity, affording about a five- and 10-fold enhancement in area-specific and mass-specific catalytic activities, respectively, compared to the standard Pt/C nanocatalyst. This solution-based synthetic route offers a new approach for constructing dendritic Pt-based nanostructures with excellent product yield, monodispersity and high crystallinity.

Published
2018
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3. Catalytic Properties of Molybdenum-Modified Platinum Nanoalloys toward Hydrogen Evolution, Oxygen Reduction Reaction, and Methanol Oxidation

Author

Gerard Malefane Leteba, David Richard Graham Mitchell, Lebohang Macheli, Pieter B. J. Levecque, Bryan P. Doyle, Eric van Steen, and Candace I. Lang

Subjects
Chemistry, Physics, Materials Chemistry, Electrochemistry, Energy Engineering and Power Technology, Chemical Engineering (miscellaneous), Electrical and Electronic Engineering, Engineering sciences. Technology
Abstract

Exploring platinum (Pt)-solute nanoparticles (NPs) with multifaceted geometries, multifunctionality, and extended stability is key for several electrocatalytic applications. Here, we demonstrate that Pt-based alloy NPs modified with molybdenum (Mo) exhibit superior electrocatalytic properties compared with pure Pt NPs. Electrocatalytic testing of these Mo-modified Pt nanoalloys shows excellent catalytic performance in the hydrogen evolution reaction (HER), the oxygen reduction reaction (ORR), and the methanol oxidation reaction (MOR). We show that the catalytic functionalities in the ORR and the MOR achieved by the Mo-modified Pt nanoalloys are 15-25 times greater than the standard commercial Pt/C nanocatalyst. These nanoalloys also show enhanced resistance to poisoning by carbon monoxide (CO) adlayers and stability after accelerated durability tests (ADTs). We associate the origin of these exceptional electrocatalytic performances of the Pt-solute-Mo nanoalloys with their high degree of concavity, variations in vertex chemistry, and Pt enrichment along the corners and edges. Our findings offer a facile synthetic approach for the synthesis of Pt-solute nanoalloys as high-performance multifunctional electrocatalysts.

Published
2022
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4. Toward understanding the utilization of oxygen reduction electrocatalysts under high mass transport conditions and high overpotentials

Author

Colleen Jackson, Xiaoqian Lin, Pieter B. J. Levecque, Anthony R. J. Kucernak, and Engineering & Physical Science Research Council (E

Subjects
oxygen reduction reaction, Science & Technology, ORR, Chemistry, Physical, rotating disc electrode, ALLOY, 0904 Chemical Engineering, kinetic activity, General Chemistry, PERFORMANCE, exchange current density, GAS-DIFFUSION ELECTRODE, FUEL-CELLS, 0305 Organic Chemistry, Catalysis, CARBON, Chemistry, ROTATING-DISC ELECTRODE, Physical Sciences, 0302 Inorganic Chemistry, floating electrode, membrane electrode assembly, CATALYST LAYER
Abstract

There is currently a disconnect between the high electrocatalyst oxygen reduction reaction (ORR) performance measured ex situ, using the rotating disc electrode (RDE), and the in situ membrane electrode assembly (MEA) performance. The disconnect in the electrocatalyst performance raises questions both about the pitfalls of the RDE technique at extrapolating the performance to higher overpotentials and how to improve the in situ catalyst layer performance to meet ambitious fuel cell targets. This work aims to bridge the gap by measuring the ORR ex situ performance under high mass transport conditions, at high overpotentials, using the floating electrode (FE) technique. Here, we determine the performance of three Pt/C electrocatalysts using the FE in 1 M HClO4 and 1 M H2SO4 to show that the MEA activities measured at 80 °C, 150 kPag were substantially lower than the room temperature and pressure performance of the same catalyst in 1 M HClO4 using the RDE and FE methods and also lower than the FE in 1 M H2SO4, implying MEA limitations are not purely due to sulfonate adsorption from the Nafion. Finally, FE and MEA data was modeled which obtained jo values on the FE (oxide free conditions) which were 4–6× larger, at 11–26 μA cm–2, than those measured on the MEA. The difference is interpreted as due to better water removal in the FE system. This work shows that MEA catalyst layers are vastly underutilized, due to poor water transport, and current densities equivalent to 10–16 A cm–2 at 0.65 V for 400 μgPt cm–2 (25–40 A mg–1) are achievable, whereas the current mass activity of MEAs is

Published
2021

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