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Non-stoichiometric NiFeMo solid solutions; tuning the hydrogen adsorption energy via molybdenum incorporation
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
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2022 (English)In: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 9, no 34, article id 2201214Article in journal (Refereed) Published
Abstract [en]

Solution precursor plasma spraying is used to produce catalytic trimetallic coatings containing Ni, Fe and Mo directly onto stainless-steel mesh, Ni foam and carbon paper. The resulting material is mostly comprised of face centered cubic FeNi3 alloy forming a highly porous coating with nanostructured features. The addition of Mo (up to ≈14 at%) generates no new crystal phases but only an increase in the lattice parameter, indicating the formation of FeNi3Mox solid solutions. The FeNi3Mox solid solutions are used as electrocatalyst for the hydrogen evolution reaction (HER) in alkaline media. The addition of Mo increases the HER activity significantly reaching an optimum performance at ≈9 at% Mo (FeNi3Mo0.40) with an overpotential at −10 mA cm−2 of 112 mV and a Tafel slope of 109 mV dec−1. The enhanced HER activity is attributed to the formation of a FeNi3Mox solid solution with an increased work function that is correlated to smaller hydrogen adsorption energies. Theoretical activity maps reveal that sites near superficial Mo atoms forms catalytic hot spots and are responsible for the observed activity.

Place, publisher, year, edition, pages
John Wiley & Sons, 2022. Vol. 9, no 34, article id 2201214
Keywords [en]
catalytic activity maps, electrocatalysis, hydrogen evolution, NiFeMo, solid solution, ternary alloy, work function
National Category
Condensed Matter Physics Physical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-200394DOI: 10.1002/admi.202201214ISI: 000864415500001Scopus ID: 2-s2.0-85139435922OAI: oai:DiVA.org:umu-200394DiVA, id: diva2:1706291
Available from: 2022-10-25 Created: 2022-10-25 Last updated: 2022-12-30Bibliographically approved
In thesis
1. Surface analysis of low dimensional materials: revealing their electronic properties by advanced spectroscopy
Open this publication in new window or tab >>Surface analysis of low dimensional materials: revealing their electronic properties by advanced spectroscopy
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Ytanalys av låg-dimensionella material : studier av elektroniska egenskaper med avancerad spektroskopi
Abstract [en]

Low-dimensional materials (0D, 1D, 2D) have been widely used to develop modern miniaturized (micro- and nano-) technology. The use of these materials come from their extraordinary optical, electrical, thermal, and mechanical properties, which are very different from the bulk crystal. To understand low-dimensional materials there is a large interest in studying the surface states of such materials, because the topmost few atomic layers possess an atomic arrangement and electronic structure different from the crystal bulk and hence responsible for many of the novel properties. 

In surface science, the techniques typically probe the topmost 1-10 nm of surfaces exposed to vacuum. X-ray photoemission spectroscopy (XPS) is the most common surface technique used because of its relatively easy handling and good ability to reveal important information on the surface oxidation states. XPS involves radiation of light that penetrates a sample up to 10 nm depth. Ultraviolet photoemission spectroscopy (UPS) is another surface-sensitive technique, with a slightly lower probing depth, on average about 2.5 nm. 

For the research in this thesis, a vacuum system has been constructed that contains surface analytical equipment for UPS, Angle Resolved Photospectroscopy and Low-electron energy diffraction. Normally, XPS and UPS are used as individual techniques as they both determine different properties of the material. However, hereby for many applications both are used in conjunction because they complement each other and provide a comprehensive analysis of the samples structure and electronic properties.

The aim of this thesis is to present surface analytical measurements carried on low-dimensional materials. Among the materials studied is Graphene, used to as a proof-of-principle experiment in the vacuum system constructed as it has been extensively studied and information can be easily found. The second material was Cu2O thin films that shows different chemical and electronic properties depending on the oxidation level. The third material is nanoporous GaN that exhibit V-pits that modify the properties of the material depending on the hole sizes. The fourth material are trigonal Te nanowires, 1D nanostructures that has a narrow direct bandgap, a high-hole mobility, and a high current density. Finally, an application of the constructed setup is show characterizing the electronic properties of NiFeMo solids. 

Abstract [sv]

Lågdimensionella material (0D, 1D, 2D) har använts i stor utsträckning för att utveckla modern miniatyriserad (mikro- och nano-) teknologi. Användningen av dessa material kommer från deras extraordinära optiska, elektriska, termiska och mekaniska egenskaper, som skiljer sig mycket från bulkkristallen. För att förstå lågdimensionella material finns det ett stort intresse av att studera deras yttillstånd, detta eftersom de översta atomskikten har en atom- och elektronstruktur som skiljer sig från kristallen i stort och således har stor inverkan för många av de egenskaperna.

Inom ytvetenskap undersöker man med de vanligaste teknikerna normalt de översta 1-10 nm av ytor exponerade i vakuum. Röntgenfotoemissionsspektroskopi (XPS) är den vanligaste yttekniken. Den används på grund av dess relativt enkla hantering och goda förmåga att ge viktig information om ytoxidationstillstånden. XPS involverar strålning av ljus som penetrerar ett prov upp till ett djup av 10 nm. Ultraviolett fotoemissionsspektroskopi (UPS) är en annan ytkänslig teknik, med ett något lägre sonderingsdjup, i genomsnitt cirka 2.5 nm. 

För forskningen i denna avhandling har ett vakuumsystem konstruerats som innehåller ytanalysutrustning för UPS, vinkelupplöst fotospektroskopi och lågelektron-energidiffraktion. Normalt används XPS och UPS som individuella tekniker eftersom de båda bestämmer olika egenskaper hos materialet. Men för många applikationer används båda i kombination eftersom de kompletterar varandra och ger en omfattande analys av provstrukturen och dess elektroniska egenskaper.

Syftet med denna avhandling är att presentera ytanalytiska mätningar utförda på lågdimensionella material. Bland de studerade materialen används grafen som ett experimentellt modellsystem för det konstruerade vakuumsystemet, detta eftersom det har studerats omfattande och information om materialet är lättillgänglig. Det andra materialet som studerades var tunna filmer av Cu2O som uppvisade olika kemiska- och elektroniska egenskaper beroende på oxidationsnivån. Det tredje materialet,  ett nanoporöst GaN med V-formade gropar som modifierar materialets egenskaper beroende på hålstorlek. Det fjärde materialet var trigonala Te nanotrådar, 1D nanostrukturer som har ett litet direkt bandgap, en hög hålrörlighet, och en hög strömtäthet. I den sista studien i avhandlingen studerades NiFeMo, ett material som tillämpas inom elektrokatalys. Uppställningen utnyttjades för att kunna korrelera vissa ytegenskaper hos materialet till de katalytiska egenskaperna för vätgasevolution. 

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2022. p. 88
Keywords
Low-dimensional materials, surface science, surface-sensitive techniques, angle-resolved photoemission spectroscopy, ultraviolet photoemission spectroscopy, electronic properties
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-200953 (URN)978-91-7855-944-2 (ISBN)978-91-7855-943-5 (ISBN)
Public defence
2022-12-06, NAT.D.320, Naturvetarhuset, Umeå, 10:15 (English)
Opponent
Supervisors
Available from: 2022-11-15 Created: 2022-11-11 Last updated: 2022-11-11Bibliographically approved

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Rafei, MounaWu, XiuyuPiñeiro-García, AlexisMiranda la Hera, VladimirWågberg, ThomasGracia-Espino, Eduardo

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