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Anodic Electrochromism for Energy-Efficient Windows: Cation/Anion-Based Surface Processes and Effects of Crystal Facets in Nickel Oxide Thin Films
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
2015 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 25, no 22, 3359-3370 p.Article in journal (Refereed) Published
Abstract [en]

Anodic electrochromic (EC) oxides are of major interest as counter electrodes for smart window applications owing to their unique optical properties upon charge insertion and extraction. However, performance optimization of such oxides has been hampered by limited understanding of their EC mechanism, particularly in Li+-conducting electrolytes. This paper reports on NiOx films with 1.16 x 1.32, prepared by sputter deposition. These films are immersed in an electrolyte of lithium perchlorate in propylene carbonate, and EC properties are studied by cyclic voltammetry and in situ optical transmittance measurements. The electrochromism is significantly enhanced at large values of x. It has been found that charge exchange in Ni oxide is mainly due to surface processes and involves both cations and anions from the electrolyte, which is different from the case of cathodic EC materials such as WO3. Whereas previous studies of Ni oxide have focused on cation intercalation, the cation/anion-based mechanism presented here offers a new paradigm for designing and developing EC devices such as smart windows for energy efficient buildings.

Place, publisher, year, edition, pages
2015. Vol. 25, no 22, 3359-3370 p.
Keyword [en]
cation, anion adsorption, electrochromism, nickel oxides, surface process
National Category
Condensed Matter Physics Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
URN: urn:nbn:se:uu:diva-256995DOI: 10.1002/adfm.201500676ISI: 000355992600012OAI: oai:DiVA.org:uu-256995DiVA: diva2:833055
Funder
EU, European Research Council, 267234
Available from: 2015-06-30 Created: 2015-06-29 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Electrochromism in Metal Oxide Thin Films: Towards long-term durability and materials rejuvenation
Open this publication in new window or tab >>Electrochromism in Metal Oxide Thin Films: Towards long-term durability and materials rejuvenation
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electrochromic thin films can effectively regulate the visible and infrared light passing through a window, demonstrating great potential to save energy and offer a comfortable indoor environment in buildings. However, long-term durability is a big issue and the physics behind this is far from clear. This dissertation work concerns two important parts of an electrochromic window: the anodic and cathodic layers. In particular, work focusing on the anodic side develop a new Ni oxide based layers and uncover degradation dynamics in Ni oxide thin films; and work focusing on the cathodic side addresses materials rejuvenation with the aim to eliminate degradation.

In the first part of this dissertation work, iridium oxide is found to be compatible with acids, bases and Li+-containing electrolytes, and an anodic layer with very superior long-term durability was developed by incorporating of small amount (7.6 at. %) of Ir into Ni oxide. This film demonstrated sustained cycle-dependent growth of charge density and electrochromic modulation even after 10,000 CV cycles. The (111) and (100) crystal facets in Ni oxide are found to possess different abilities to absorb cation and/or anion, which yields different degrees of coloration and this is very significant for the electrochromic properties. The degradation of charge capacity in Ni oxide has an inevitable rapid decay in the first hundreds of cycles, subsequently combined with a more gradual decay, which is independent of applied potential and film composition. The consistent phenomenon can be very well modeled by power-law or stretched exponential decay; however the two models are indistinguishable in the current stage. Interestingly, in both models, the power-law exponent is 0.2 ≤ p ≤ 0.8, with most of the values around 0.5, in line with normal or anomalous diffusion models.

The second part of dissertation work deals with cathodic WO3 and TiO2. WO3 suffers from ion trapping induced degradation of charge capacity and optical modulation upon electrochemical cycling. This speculation is strongly supported by direct evidence from Time-of-Flight Elastic Recoil Detection Analysis (ToF-ERDA). Most importantly, this ion trapping induced degradation can be eliminated by a galvanostatic de-trapping process. Significant ion-trapping takes place when x exceeds ~0.65 in LixWO3. The trapped ions are stable in the host structure, meaning that the ions cannot de-trap without external stimuli. The similar work done on TiO2 significantly complements and extends the work on the recuperation of WO3; the difference is that the trapped ions in host TiO2 seem to be less stable compared with the trapped ions in WO3.

    Overall, this dissertation presents a refined conceptual framework for developing superior electrochromic windows in energy efficient buildings.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 86 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1323
Keyword
electrochromic, smart windows, long-term durability, degradation kinetics, ion trapping, de-trapping, materials rejuvenation
National Category
Nano Technology Condensed Matter Physics Materials Engineering Energy Systems Composite Science and Engineering
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-267111 (URN)978-91-554-9421-6 (ISBN)
Public defence
2016-01-14, Polhemalen, Ångströmlaboratoriet, Lägerhyddsv. 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Funder
EU, European Research Council
Available from: 2015-12-14 Created: 2015-11-18 Last updated: 2016-01-28

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Wen, Rui-TaoGranqvist, Claes G.Niklasson, Gunnar A.

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