Synthesis of Platinum Rare Earth Alloy Catalysts for Fuel Cells

176 Pages·2017·25.01 MB·English

Downloaded from orbit.dtu.dk on: Mar 04, 2023

Synthesis of Platinum Rare Earth Alloy Catalysts for Fuel Cells
Knudsen, Brian Peter
Publication date:
2016
Document Version
Publisher's PDF, also known as Version of record
Link back to DTU Orbit
Citation (APA):
Knudsen, B. P. (2016). Synthesis of Platinum Rare Earth Alloy Catalysts for Fuel Cells. Department of Physics,
Technical University of Denmark.

General rights
Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright
owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.

 Users may download and print one copy of any publication from the public portal for the purpose of private study or research.
 You may not further distribute the material or use it for any profit-making activity or commercial gain
 You may freely distribute the URL identifying the publication in the public portal

If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately
and investigate your claim.
Synthesis of Platinum Rare Earth
Alloy Catalysts for Fuel Cells
PhD dissertation by
Brian Peter Knudsen
Supervisor: Professor Ib Chorkendorff
Co-supervisor: Associate Professor Ifan E. L. Stephens
Kongens Lyngby 2016
This is the description of the front page image
Technical University of Denmark
Department of Physics
Center for Individual Nanoparticle Functionality (CINF)
Fysikvej, building 311,
2800 Kongens Lyngby, Denmark
Phone [phone]
[email protected]
www.fysik.dtu.dk
Preface
ThisthesisissubmittedaspartialfulfilmentofthePhDdegreeinphysicsatthe
Technical University of Denmark (DTU). The work herein was carried out at
theDepartmentofPhysicsandtheCenterforIndividualNanoparticleFunction-
ality (CINF), from December 2012 until June 2016. The work was supervised
by professor Ib Chorkendorff and associate professor Ifan E. L. Stephens. The
work was funded by The Department of Physics and in part by the Innovation
Fund Denmark project NACORR, project no. 12-132695.
I would like to thank my supervisors for granting me the opportunity to work
on such a challenging but rewarding project and for the sublime research en-
vironment they have established. With great possibilities both physical, in the
form of facilities, and mentally in the form of a stimulating atmosphere formed
by former and present colleagues. I would like to thank them all for making
my time at CINF so memorable. They have always been happy to share and
discuss ideas, both those useful for the work and also those without any mean-
ing. A special thank you has to go to the persons at CINF that I have had the
pleasure of working directly with during my PhD studies: Amado Velázquez-
Palenzuela, Claudie Roy, Christoffer Mølleskov Pedersen, Paolo Malacrida, Pa-
triciaHernandez-FernandezandJacquelineMcAnulty. RobertJensenandKen-
neth Nielsen have also been of great help with their knowledge and repair work
on the Theta Probe. I would also like to thank my colleagues that had to share
an office with me and especially Rasmus Frydendal, whom I have had the plea-
sureofstudyingwithsince2007. Ihavealwaysenjoyedourconversationsabout
everything and nothing.
I also have to thank my family for their understanding in the last period of the
project and for always supporting me, and encouraging me when I first started
to dabble with the idea of studying physics back in primary school. Finally,
Tine has been the one carrying me through it all, always there to pick me up
if I was down, always ready to be there if needed. Without her I would never
have made it. I look forward to spend far more time with you and see where
things will take us from here.
Kongens Lyngby, 14th June 2016
Brian Peter Knudsen
ii
Abstract
This PhD thesis presents the work performed on synthesising catalytically ac-
tive platinum rare earth alloys for use in fuel cells. For fuel cells to become an
integral part of the future transportation sector, the activity of platinum, the
cathode catalyst of choice, has to be improved significantly. Alloying is a com-
mon way to improve the activity of platinum, however, true long term stability
of the common alloys of platinum and late transition metals is unknown and
could suffer from the low heat of formation.
A group of alloys that are active and have strong heats of formation, possibly
enabling enhanced long term stability, is those of platinum and the rare earth
elements. These have shown six fold improvement over pure platinum, for bulk
crystals,andanimpressivemassactivityof3.6A mg−1 formassselectedPt Gd
Pt x
nanoparticles, prepared by magnetron sputtering. However, these alloys have
not yet been produced by a scalable method that allows for practical applica-
tion.
Herein methods for scalable synthesis of carbon supported platinum rare earth
alloys are explored. Cathodic corrosion proved promising given further optimi-
sation are done, however, high temperature reduction of rare earth precursors
into commercial Pt/C was found to be the most promising method. The ther-
modynamicsofthesystemwasexploredandthesynthesisisfoundtobefeasible
at temperatures from 500◦C. The many alloy phases for platinum rare earth
alloys, that are very closely related in structure, complicated the characterisa-
tion of the system.
ThroughoptimisationoftheinitialsynthesissetupanactivePt-Yalloycatalyst
was formed showing an increase in mass activity from 0.27±0.07A mg−1 to
Pt
0.41±0.01A mg−1. This initial activity for a new group of catalysts, produced
Pt
forthefirsttimebyascalablemethodisverypromising. However,furtherwork
into phase purity and alloying conditions is needed to fully realise the potential
of this group of catalysts.
iv
Resume
Denne ph.d. afhandling præsenterer arbejdet med, at syntetisere katalytisk ak-
tive legeringer mellem platin og de sjældne jordarter til brug i brændselsceller.
For at brændselsceller kan blive en væsentlig del af den fremtidige transport-
sektor skal aktiviteten af platin, som er den foretrukne katodekatalysator, øges
drastisk. En ofte anvendt metode til, at øge aktiviteten af platin er at legere
det med et af de sene overgangsmetaller. Den endelige Stabilitet af disse leg-
eringer i brændselscellemiljøet er dog ukendt, og kan fejle på grund af den lave
formationsenergi for disse legeringer.
En gruppe af legeringer der både er aktive og har høje formationsenergier, der
muligvis kan sikre høj stabilitet, er legeringer mellem platin og de sjældne jor-
darter. Disse legeringer har udvist seks gange den aktivitet der ses for platin
nårdermålespåmakroskopiskekrystaller. FormassefiltreredePt Gdnanopar-
x
tikler, fremstillet med magnetron katodeforstøvning, har masse aktivitet været
imponerende med 3.6A mg−1 . Disse legeringer er dog aldrig blevet fremstillet
Pt
med en skalerbar metode der tillader praktiske anvendelser.
Heri bliver metoder for den skalerbare syntese af legeringer mellem platin og de
sjældne jordarter undersøgt. Katodisk korrosion viste sig at være lovende, hvis
yderligereoptimeringafparametrenefindersted,mendenmestlovendemetode
var modifikationen af en kommerciel Pt/C katalysator ved høj temperaturs re-
duktion af salte af sjældne jordarter. Termodynamikken bag dette system blev
undersøgt og det viste sig muligt, at danne de ønskede legeringer fra 500◦C.
De mange legeringsfaser, hvis strukturer er tæt relaterede med hinanden og
som kan dannes for fasesystemet mellem platin og de sjældne jordarter, kom-
plicerede karakteriseringen af systemet.
En aktiv Pt-Y legering blev syntetiseret efter en optimering af opsætningen
til syntesen. Denne udviste en masse aktivitet på 0.41 ± 0.01A mg−1 mod
Pt
0.27±0.07A mg−1 fordenkommerciellekatalysator. Denneaktiviteterlovende
Pt
eftersom dette er første gang denne nye gruppe af katalysatorer, bliver syntetis-
eret med en skalerbar metode. Der skal dog fortsat arbejdes med faserenheden
og synteseparametrene for, at kunne udnytte denne gruppe af katalysatorers
fulde potentiale.
vi
List of Included Papers
Appended Papers
Paper I
Scalable Synthesis of Carbon Supported Platinum - Rare Earth
Alloys for use as Fuel Cell Cathodes
Brian P. Knudsen, Christoffer M. Pedersen, Amado Velázquez-Palenzuela, Leif
H. Christensen, Ifan E. L. Stephens, Ib Chorkendorff,
In preparation
Papers Not Appended
Paper II
Benchmarking the Stability of Oxygen Evolution Reaction Cat-
alysts: The Importance of Monitoring Mass Losses
Rasmus Frydendal, Elisa A. Paoli, Brian P. Knudsen, Björn Wickman, Paolo
Malacrida, Ifan E.L. Stephens, Ib Chorkendorff
ChemElectroChem, 2014, Volume 1, pages 2075-2081