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Strongly Improved Electrochemical Cycling Durability by Adding Iridium to Electrochromic Nickel Oxide 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.ORCID iD: 0000-0002-8279-5163
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
2015 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, no 18, 9319-9322 p.Article in journal (Refereed) Published
Abstract [en]

Anodically colored nickel oxide (NiO) thin films :are of much interest as counter electrodes in tungsten oxide based electrochromic devices such as "smart windows" for energy-efficient buildings. However, NiO films are prone to Suffering severe charge density degradation upon prolonged electrochemical cycling, which can lead to insufficient device lifetime. Therefore, a means to improve the durability of NiO-based films is an important challenge at present. Here we report that the incorporation of a modest amount of iridium into NiO films [Ir/(Ir + Ni) = 7.6 atom %] leads to remarkable durability, exceeding 10000 cycles in a lithium-conducting, electrolyte, along with significantly improved optical modulation during extended cycling. Structure characterization showed that the face-centered-cubic-type NiO structure remained after iridium addition. Moreover, the crystallinity of these films was enhanced upon electrochemical cycling.

Place, publisher, year, edition, pages
2015. Vol. 7, no 18, 9319-9322 p.
Keyword [en]
electrochromic, iridium-nickel oxide, improved durability, charge density, optical modulation
National Category
Nano Technology
URN: urn:nbn:se:uu:diva-256240DOI: 10.1021/acsami.5b01715ISI: 000354906500002PubMedID: 25919917OAI: oai:DiVA.org:uu-256240DiVA: diva2:826080
EU, European Research Council, 267234
Available from: 2015-06-24 Created: 2015-06-22 Last updated: 2016-01-13Bibliographically 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.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1323
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
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)
EU, European Research Council
Available from: 2015-12-14 Created: 2015-11-18 Last updated: 2016-01-28

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