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Wang, J., Xu, C., Nilsson, A. M., Fernandes, D. L. A. & Niklasson, G. A. (2019). A novel phase function describing light scattering of layers containing colloidal nanospheres. Nanoscale, 11(15), 7404-7413
Open this publication in new window or tab >>A novel phase function describing light scattering of layers containing colloidal nanospheres
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2019 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 11, no 15, p. 7404-7413Article in journal (Refereed) Published
Abstract [en]

Light scattering from small particles exhibit unique angular scattering distributions, which are strongly dependent on the radius to wavelength ratio as well as the refractive index contrast between the particles and the surrounding medium. As the concentration of the particles increases, multiple scattering becomes important. This complicates the description of the angular scattering patterns, and in many cases one has to resort to empirical phase functions. We have measured the angle dependence of light scattering from a polymer layer containing sub-micron metallic and dielectric particles. The samples exhibited strongly forward and backward peaked scattering patterns, which were fitted to a number of empirical approximative phase functions. We found that a novel two-term Reynolds-McCormick (TTRM) phase function gave the best fit to the experimental data in all cases. The feasibility of the TTRM approach was further validated by good agreement with numerical simulations of Mie single scattering phase functions at various wavelengths and sizes, ranging from the Rayleigh scattering regime to the geometrical optics regime. Hence, the widely adaptable TTRM approach is able to describe angular scattering distributions of different kinds of nanospheres and nanocomposites, both in the single scattering and multiple scattering regimes.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-383188 (URN)10.1039/c9nr01707k (DOI)000465315900034 ()30938744 (PubMedID)
Funder
Swedish Research Council, 2016-03713
Available from: 2019-07-25 Created: 2019-07-25 Last updated: 2019-07-25Bibliographically approved
Granqvist, C. G., Arvizu, M. A., Qu, H.-Y., Wen, R.-T. & Niklasson, G. (2019). Advances in electrochromic device technology: Multiple roads towards superior durability. Paper presented at 61st Annual Technical Conference of the Society-of-Vacuum-Coaters (SVC), MAY 05-10, 2018 , Orlando, FL, USA.. Surface & Coatings Technology, 357, 619-625
Open this publication in new window or tab >>Advances in electrochromic device technology: Multiple roads towards superior durability
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2019 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 357, p. 619-625Article in journal (Refereed) Published
Abstract [en]

Most electrochromic (EC) devices must have a service lifetime of many years, and this is particularly so for“smart windows” in buildings with good energy efficiency and indoor comfort. The central part of oxide-based EC devices contains thin films based on W oxide and Ni oxide together with an interposed electrolyte. Depending on operating conditions, these films may show degradation at a slower or faster pace, and means to prevent or reverse this phenomenon, or as a minimum allow reliable lifetime prediction, have been sought ever since the beginnings of EC technology. Here we survey recent endeavors related to EC films of W oxide and Ni oxide and show that (i) electrochemical pretreatment of films in a liquid electrolyte can significantly improve durability, (ii)electrochemical posttreatment in a liquid electrolyte can rejuvenate degraded films, (iii) mixed oxides can have better durability and optical performance than corresponding pure oxides, and (iv) lifetime prediction is possible.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Materials Chemistry
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-369882 (URN)10.1016/j.surfcoat.2018.10.048 (DOI)000455691100083 ()
Conference
61st Annual Technical Conference of the Society-of-Vacuum-Coaters (SVC), MAY 05-10, 2018 , Orlando, FL, USA.
Funder
EU, European Research Council, 267234
Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2019-02-05Bibliographically approved
Cindemir, U., Topalian, Z., Granqvist, C. G., Österlund, L. & Niklasson, G. (2019). Characterization of nanocrystalline-nanoporous nickel oxide thin films prepared by reactive advanced gas deposition. Materials Chemistry and Physics, 227, 98-104
Open this publication in new window or tab >>Characterization of nanocrystalline-nanoporous nickel oxide thin films prepared by reactive advanced gas deposition
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2019 (English)In: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 227, p. 98-104Article in journal (Refereed) Published
Abstract [en]

Nanocrystalline-nanoporous Ni oxide is of much interest for gas sensors and other applications. Reactive advanced gas deposition (AGD) stands out as a particularly promising technique for making thin films of this material owing to the techniques ability to separate between the growth of individual nanoparticles and their subsequent deposition to create a consolidated material on a substrate. Here we report on the characterization of Ni oxide films, made by reactive AGD, by several methods. X-ray diffractometry showed that the films had a face centered cubic NiO structure, and scanning electron microscopy indicated a compact nanoparticulate composition. X-ray photoelectron spectroscopy showed the presence of Ni3+ and demonstrated that these states became less prominent upon heat treatment in air. Extended x-ray absorption fine structure analysis elucidated the local atomic structure; in particular, data on interatomic distances and effects of annealing on local disorder showed that the Ni oxide nanoparticles crystallize upon annealing while maintaining their nanoparticle morphology, which is a crucial feature for reproducible fabrication of Ni oxide thin films for gas sensors. Importantly, several techniques demonstrated that grain growth remained modest for annealing temperatures as high as 400 degrees C for 1700-nm-thick films. The present article is a sequel to an earlier one [U. Cindemir et al., Sensors and Actuators B 242 (2017) 132-139] in which we reported on fluctuation-enhanced and conductometric gas sensing with Ni oxide films prepared by AGD.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Nickel oxide, Advanced gas deposition, EXAFS, Atomic structure, Gas sensor
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-387223 (URN)10.1016/j.matchemphys.2019.01.058 (DOI)000466617800013 ()
Funder
EU, FP7, Seventh Framework Programme, 267234
Available from: 2019-06-25 Created: 2019-06-25 Last updated: 2020-01-31Bibliographically approved
Qiu, Z., Tai, C.-W., Niklasson, G. & Edvinsson, T. (2019). Direct observation of active catalyst surface phases and the effect of dynamic self-optimization in NiFe-layered double hydroxides for alkaline water splitting. Energy & Environmental Science, 12(2), 572-581
Open this publication in new window or tab >>Direct observation of active catalyst surface phases and the effect of dynamic self-optimization in NiFe-layered double hydroxides for alkaline water splitting
2019 (English)In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 12, no 2, p. 572-581Article in journal (Refereed) Published
Abstract [en]

Earth-abundant transition metal-based compounds are of high interest as catalysts for sustainable hydrogen fuel generation. The realization of effective electrolysis of water, however, is still limited by the requirement of a high sustainable driving potential above thermodynamic requirements. Here, we report dynamically self-optimized (DSO) NiFe layered double hydroxide (LDH) nanosheets with promising bi-functional performance. Compared with pristine NiFe LDH, DSO NiFe LDH exhibits much lower overpotential for the hydrogen evolution reaction (HER), even outperforming platinum. Under 1 M KOH aqueous electrolyte, the bi-functional DSO catalysts show an overpotential of 184 and -59 mV without iR compensation for oxygen evolution reaction (OER) and HER at 10 mA cm(-2). The material system operates at 1.48 V and 1.29 V to reach 10 and 1 mA cm(-2) in two-electrode measurements, corresponding to 83% and 95% electricity-to-fuel conversion efficiency with respect to the lower heating value of hydrogen. The material is seen to dynamically reform the active phase of the surface layer during HER and OER, where the pristine and activated catalysts are analyzed with ex situ XPS, SAED and EELS as well as with in situ Raman spectro-electrochemistry. The results show transformation into different active interfacial species during OER and HER, revealing a synergistic interplay between iron and nickel in facilitating water electrolysis.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:uu:diva-379268 (URN)10.1039/c8ee03282c (DOI)000459741700005 ()
Funder
Swedish Energy AgencySwedish Research Council, VR-2016-03713Swedish Research Council Formas, 2016-00908Knut and Alice Wallenberg Foundation
Available from: 2019-03-18 Created: 2019-03-18 Last updated: 2019-03-29Bibliographically approved
Niklasson, G. & Granqvist, C. G. (2019). Electrochromic and Thermochromic Oxide Materials. Applied Surface Science, 482, 70-72
Open this publication in new window or tab >>Electrochromic and Thermochromic Oxide Materials
2019 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 482, p. 70-72Article in journal (Other academic) Published
National Category
Condensed Matter Physics Energy Systems
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-398772 (URN)10.1016/j.apsusc.2017.11.255 (DOI)
Available from: 2019-12-10 Created: 2019-12-10 Last updated: 2020-02-07Bibliographically approved
Arvizu, M. A., Qu, H.-Y., Cindemir, U., Qiu, Z., Rojas González, E. A., Primetzhofer, D., . . . Niklasson, G. (2019). Electrochromic WO3 thin films attain unprecedented durability by potentiostatic pretreatment. Journal of Materials Chemistry A, 7(6), 2908-2918
Open this publication in new window or tab >>Electrochromic WO3 thin films attain unprecedented durability by potentiostatic pretreatment
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2019 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, no 6, p. 2908-2918Article in journal (Refereed) Published
Abstract [en]

Electrochromic windows and glass facades are able to impart energy efficiency jointly with indoor comfort and convenience. Long-term durability is essential for practical implementation of this technology and has recently attracted broad interest. Here we show that a simple potentiostatic pretreatment of sputterdeposited thin films of amorphous WO3-the most widely studied electrochromic material-can yield unprecedented durability for charge exchange and optical modulation under harsh electrochemical cycling in a Li-ion-conducting electrolyte and effectively evades harmful trapping of Li. The pretreatment consisted of applying a voltage of 6.0 V vs. Li/Li+ for several hours to a film backed by a transparent conducting In2O3: Sn layer. Associated compositional and structural modifications were probed by several techniques, and improved durability was associated with elemental intermixing at the WO3/ITO and ITO/glass boundaries as well as with carbonaceous solid-electrolyte interfacial layers on the WO3 films. Our work provides important new insights into long-term durability of ion-exchange-based devices.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-378529 (URN)10.1039/c8ta09621j (DOI)000457893400054 ()
Funder
EU, European Research Council, 267234Swedish Research Council, 821-2012-5144Swedish Research Council, 2017-00646_9Swedish Foundation for Strategic Research , RIF14-0053
Available from: 2019-03-22 Created: 2019-03-22 Last updated: 2019-03-22Bibliographically approved
Arvizu, M., Qu, H.-Y., Cindemir, U., Qiu, Z., Rojas-González, E., Primetzhofer, D., . . . Niklasson, G. (2019). Electrochromic WO3 Thin Films Attain Unprecedented Durability by Potentiostatic Pretreatment. Journal of Materials Chemistry, A(7), 2908-2918
Open this publication in new window or tab >>Electrochromic WO3 Thin Films Attain Unprecedented Durability by Potentiostatic Pretreatment
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2019 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. A, no 7, p. 2908-2918Article in journal (Other academic) Published
Abstract [en]

Electrochromic windows and glass facades are able to impart energy efficiency jointly with indoor comfort and convenience. Long-term durability is essential for practical implementation of this technology and has recently attracted broad interest. Here we show that a simple potentiostatic pretreatment of sputter-deposited thin films of amorphous WO3-the most widely studied electrochromic material-can yield unprecedented durability for charge exchange and optical modulation under harsh electrochemical cycling in a Li-ion-conducting electrolyte and effectively evades harmful trapping of Li. The pretreatment consisted of applying a voltage of 6.0 V vs. Li/Li+ for several hours to a film backed by a transparent conducting In2O3:Sn layer. Associated compositional and structural modifications were probed by several techniques, and improved durability was associated with elemental intermixing at the WO3/ITO and ITO/glass boundaries as well as with carbonaceous solid-electrolyte interfacial layers on the WO3 films. Our work provides important new insights into long-term durability of ion-exchange-based devices.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-398767 (URN)10.1039/c8ta09621j (DOI)
Available from: 2019-12-10 Created: 2019-12-10 Last updated: 2020-02-07Bibliographically approved
Sorar, I., Rojas-González, E., Bayrak Pehlivan, I., Granqvist, C. G. & Niklasson, G. (2019). Electrochromism of W–Ti Oxide Films: Cycling Durability, Potentiostatic Rejuvenation, and Modeling of Electrochemical Degradation. Journal of the Electrochemical Society, 166, H795-H801
Open this publication in new window or tab >>Electrochromism of W–Ti Oxide Films: Cycling Durability, Potentiostatic Rejuvenation, and Modeling of Electrochemical Degradation
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2019 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 166, p. H795-H801Article in journal (Other academic) Published
Abstract [en]

Thin films of electrochromic W oxide and W–Ti oxide were prepared by reactive DC magnetron sputtering and were cycled voltammetrically in an electrolyte of lithium perchlorate in propylene carbonate. Film degradation was studied for up to 500 voltammetric cycles in voltage ranges between 1.5–4.0 and 2.0–4.0 V vs. Li/Li+. Optically and electrochemically degraded films were subjected to potentiostatic posttreatment at 6.0 V vs. Li/Li+ to achieve ion de-trapping and rejuvenation so that the films partly regained their original properties. Ti incorporation and potentiostatic posttreatment jointly yielded superior electrochromic properties provided the lower limit of the voltage range was above 1.6–1.7 V vs. Li/Li+. Degradation dynamics for as-deposited and rejuvenated thin films was modeled successfully by power-law kinetics; this analysis indicated coexistence of two degradation mechanisms, one based on dispersive chemical kinetics and operating universally and another, of unknown origin, rendered inactive by rejuvenation. The results of the present study are of large interest for the development of electrochromic devices with exceptional durability.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-398775 (URN)10.1149/2.0421915jes (DOI)
Available from: 2019-12-10 Created: 2019-12-10 Last updated: 2020-02-14Bibliographically approved
Sorar, I., Rojas González, E. A., Bayrak Pehlivan, I., Granqvist, C. G. & Niklasson, G. (2019). Electrochromism of W–Ti Oxide Thin Films: Cycling Durability,Potentiostatic Rejuvenation, and Modelling of Electrochemical Degradation. Journal of the Electrochemical Society, 166(15), H795-H801
Open this publication in new window or tab >>Electrochromism of W–Ti Oxide Thin Films: Cycling Durability,Potentiostatic Rejuvenation, and Modelling of Electrochemical Degradation
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2019 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 166, no 15, p. H795-H801Article in journal (Refereed) Published
Abstract [en]

Thin films of electrochromicWoxide and W–Ti oxide were prepared by reactive DC magnetron sputtering and were cycled voltammetrically in an electrolyte of lithium perchlorate in propylene carbonate. Film degradation was studied for up to 500 voltammetric cycles in voltage ranges between 1.5–4.0 and 2.0–4.0 V vs. Li/Li+. Optically and electrochemically degraded films were subjected to potentiostatic posttreatment at 6.0 V vs. Li/Li+ to achieve ion de-trapping and rejuvenation so that the films partly regained their original properties. Ti incorporation and potentiostatic posttreatment jointly yielded superior electrochromic properties provided the lower limit of the voltage range was above 1.6–1.7 V vs. Li/Li+. Degradation dynamics for as-deposited and rejuvenated thin films was modeled successfully by power-law kinetics; this analysis indicated coexistence of two degradation mechanisms, one based on dispersive chemical kinetics and operating universally and another, of unknown origin, rendered inactive by rejuvenation. The results of the present study are of large interest for the development of electrochromic devices with exceptional durability.

Place, publisher, year, edition, pages
Electrochemical Society, 2019
National Category
Condensed Matter Physics
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-397482 (URN)DOI: 10.1149/2.0421915jes (DOI)000494283100001 ()
Funder
Swedish Research Council, VR-2016-03713Swedish Research Council, 2017-00646-9Swedish Foundation for Strategic Research , RIF14-0053
Available from: 2019-11-20 Created: 2019-11-20 Last updated: 2019-11-22Bibliographically approved
Bayrak Pehlivan, I., Arvizu, M. A., Qiu, Z., Niklasson, G. A. & Edvinsson, T. (2019). Impedance Spectroscopy Modeling of Nickel–Molybdenum Alloys on Porous and Flat Substrates for Applications in Water Splitting. The Journal of Physical Chemistry C, 123(39), 23890-23897
Open this publication in new window or tab >>Impedance Spectroscopy Modeling of Nickel–Molybdenum Alloys on Porous and Flat Substrates for Applications in Water Splitting
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2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 39, p. 23890-23897Article in journal (Refereed) Published
Abstract [en]

Hydrogen production by splitting water using electrocatalysts powered by renewable energy from solar or wind plants is one promising alternative to produce a carbon-free and sustainable fuel. Earth-abundant and nonprecious metals are, here, of interest as a replacement for scarce and expensive platinum group catalysts. Ni–Mo is a promising alternative to Pt, but the type of the substrate could ultimately affect both the initial growth conditions and the final charge transfer in the system as a whole with resistive junctions formed in the heterojunction interface. In this study, we investigated the effect of different substrates on the hydrogen evolution reaction (HER) of Ni–Mo electrocatalysts. Ni–Mo catalysts (30 atom % Ni, 70 atom % Mo) were sputtered on various substrates with different porosities and conductivities. There was no apparent morphological difference at the surface of the catalytic films sputtered on the different substrates, and the substrates were classified from microporous to flat. The electrochemical characterization was carried out with linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in the frequency range 0.7 Hz–100 kHz. LSV measurements were carried out at direct current (DC) potentials between 200 and −400 mV vs the reversible hydrogen electrode (RHE) in 1 M NaOH encompassing the HER. The lowest overpotentials for HER were obtained for films on the nickel foam at all current densities (−157 mV vs RHE @ 10 mA cm–2), and the overpotentials increased in the order of nickel foil, carbon cloth, fluorine-doped tin oxide, and indium tin oxide glass. EIS data were fitted with two equivalent circuit models and compared for different DC potentials and different substrate morphologies and conductivities. By critical evaluation of the data from the models, the influence of the substrates on the reaction kinetics was analyzed in the high- and low-frequency regions. In the high-frequency region, a strong substrate dependence was seen and interpreted with a Schottky-type barrier, which can be rationalized as being due to a potential barrier in the material heterojunctions or a resistive substrate–film oxide/hydroxide. The results highlight the importance of substrates, the total charge transfer properties in electrocatalysis, and the relevance of different circuit components in EIS and underpin the necessity to incorporate high-conductivity, chemically inert, and work-function-matched substrate–catalysts in the catalyst system.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
National Category
Materials Chemistry
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-395176 (URN)10.1021/acs.jpcc.9b02714 (DOI)000489086300017 ()
Funder
EU, Horizon 2020Swedish Research Council, VR-2015-03814Swedish Research Council, VR-2016-03713
Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-12-12Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-8279-5163

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