Metal Oxide Electrochromism

Nanomaterials of undoped vanadia employed in electrochromic studies include nanowires [35-37], inverse opals [34], and mesoporous films [38]. Similar attempts were undertaken for NiO devices [39 2]. Although these recent attempts brought about an improvement in electrochromic performance, the reported switching times remained 1-2 orders of magnitude above the desired video rate of 24 frames per second [34-38]. This is mainly due to the use of sub-optimal MO morphologies in terms of their structural dimension, connectivity and integrity. 

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The Donnelly Corporation have also devised a rear-view mirror using an hybrid system. A metal oxide electrochromic layer is used in conjunction with a non-elec-trochromic reversible redox complex in the contacting solution. ... 

W. Dautremont-Smith. Transition metal oxide electrochromic materials and displays A review - 1. oxides with cathodic coloration. Displays, 3(1) 3-22, January 1982. 

Metal Oxide Electrochromism Viologen Electrochromism Prussian Blue Electrochromism Conducting Polymer Electrochromism... 

Dautremont-Smith WC (1982) Transition metal oxide electrochromic materials and displays a review. Part 2. Oxides with anodic coloration. Displays 3(3) 67-80 Delahay P (1965) Double Layer and Electrode Kinetics. Interscience Publishers, New York Pletcher D, Walsh FC (1990) Industrial Electrochemistry, second edition. Chapman and Hall, London... 

Metal Oxides Tungsten trioxide, undoubtedly the most widely studied electrochromic material, is used in several types of commercial electrochromic devices. 

Metal oxide sensors (MOS), smart, 22 717 Metal oxide supported catalysts, 5 336-337 coke formation on, 5 267—270 Metal passivation, in industrial water treatment, 26 137 Metal peroxides, 18 410 Metal phosphates, tertiary, 18 840 Metal-phosphorus alloys, 19 59 Metal phthalocyanines, electrochromic materials, 6 572t, 576-577 Metal prefinishing, detersive systems for, 8 413t... 

Synthesis and electrochromic properties of nanocarbon-metal oxide hybrids... 

Examples for electrochromic behavior upon electrochemical oxidation can be found among group VIII metal oxides. Thin films of transparent hydrated iridium oxide turn blue-black, whereas nickel oxide switches from pale green to brown-black, possibly due to the absorbance of Ni3+ centers [26]. The systems are much less thoroughly investigated and a detailed mechanistic explanation is not known. However, proton extraction and anion insertion have been suggested. 

Metal-oxide-based electrochromic systems are especially interesting for the development of electrochromic windows because they mostly switch from a transparent state to a dark colored state [38,39]. In addition, their relatively slow response times are acceptable for this kind of application, possibly even preferable from an aesthetic point of view. Again, W03 has seen the most use in the development of actual devices. Several different deposition techniques have been applied. For example, a prototype electrochromic window based on W03 with reasonable dimensions (0.7 X 1 m) has been assembled that reduces light transmission by a factor of 4 in its colored state [28]. 

A review of recent research, as well as new results, are presented on transition metal oxide clusters, surfaces, and crystals. Quantum-chemical calculations of clusters of first row transition metal oxides have been made to evaluate the accuracy of ab initio and density functional calculations. Adsorbates on metal oxide surfaces have been studied with both ab initio and semi-empirical methods, and results are presented for the bonding and electronic interactions of large organic adsorbates, e.g. aromatic molecules, on Ti02 and ZnO. Defects and intercalation, notably of H, Li, and Na in TiC>2 have been investigated theoretically. Comparisons with experiments are made throughout to validate the calculations. Finally, the role of quantum-chemical calculations in the study of metal oxide based photoelectrochemical devices, such as dye-sensitized solar cells and electrochromic displays, is discussed. 

The results obtained for the solar cell discussed above suggest a strong interaction between the chromophore and the metal oxide layer, a large surface area, thus yielding large absorbances, and an efficient charge-separation upon injection. Several studies have indeed been carried out in an attempt to utilize the potential of nanocrystalline metal oxides as substrates for electrochromic devices. A particularly interesting approach has been reported by Fitzmaurice and co-workers [17]. These authors have constructed an electrochromic device based on the combination of... 

Since mesoporous materials contain pores from 2 nm upwards, these materials are not restricted to the catalysis of small molecules only, as is the case for zeolites. Therefore, mesoporous materials have great potential in catalytic/separation technology applications in the fine chemical and pharmaceutical industries. The first mesoporous materials were pure silicates and aluminosilicates. More recently, the addition of key metallic or molecular species into or onto the siliceous mesoporous framework, and the synthesis of various other mesoporous transition metal oxide materials, has extended their applications to very diverse areas of technology. Potential uses for mesoporous smart materials in sensors, solar cells, nanoelectrodes, optical devices, batteries, fuel cells and electrochromic devices, amongst other applications, have been suggested in the literature.11 51... 

Iridium dioxide — Iridium oxide crystallizes in the rutile structure and is the best conductor among the transition metal oxides, exhibiting metallic conductivity at room temperature. This material has established itself as a well-known - pH sensing [i] and electrochromic [ii] material (- electrochromism) as well as a catalytic electrode in the production of chlorine and caustic [iii]. The oxide may be prepared thermally [iv] (e.g., by thermal decomposition of suitable precursors at temperatures between 300 and 500 °C to form a film on a substrate such as titanium) or by anodic electrodeposition [v]. 

Metal oxides which undergo proton insertion reactions find extensive application in batteries and are currently being investigated as potential electrochromic materials. The properties of battery oxides, e.g. manganese dioxide [107-110] and nickel [111-114] have been extensively reviewed in the literature and will therefore not be discussed here. Rather, the properties of electrochemically grown, electrochromic oxide films will be described since this is a relatively new and interesting field. 

Metal oxide films which change color in an electrolyte with change in applied potential [11, 115-123,127, 128, 137] have attracted a lot of attention in the past 15 years or so because of their potential application in electrochromic displays. Tungsten trioxide was the first oxide to receive significant attention in this regard [115-119] and, later, Ir oxide films [11, 120, 121, 127,... 

In general, metal oxides are very common inorganic commodities, widely applied, and display an assortment of unique chemical and physical properties. They are accessible by different techniques including chemical vapor deposition and sol-gel methods. Their technological application extends from super- and semiconducting materials to electrochromic devices, optical filters, protective coatings and solar absorbers ... 

The presence of alkali metal ions is crucial for the stabilization of excess charge trapped within the nanopartides. Intercalation of metal ions within the nanoparticle thus becomes a limiting factor as the rate of transport of these ions becomes slower in thicker metal oxide films. This in turn controls the rate of coloration and recovery of the electrochromic effects. Limited efforts have also been made to employ mixed Ti02/W03 [145], WO3/V2O5 [146], and WO3/M0O3 [147] systems to enhance the efficiency of electrochromic effects. The beneficial aspect of these nanostructured semiconductor films in electrochromic devices is yet to be explored in a systematic way. 

As shown in this symposium, interest in chemical modification of electrode surfaces has been extended in many directions, including the study of light-assisted redox reactions, and the use of modified electrodes in electrochromic devices (1,2). Our own studies have centered on the study of metal and metal oxide electrodes modified with very thin films of phthalocyanines (PC) and on the electrochromic reaction of n-heptyl viologen on metal oxide electrodes, and on the effect on these reactions of changing substrate chemical and physical composition (A,5). 

Solid isopoly- and heteropolymetalate compounds have been synthesized. Within this group of materials, one can include the so-called metal oxide bronzes (typically tungsten bronzes). Starting from WO, electrochemical reduction processes yield intercalation materials with electrochromic properties (Grandqvist, 1999). 

The phenomenon of electrochromism can be defined as the change of the optical properties of a material due to the action of an electric field. The field reversal allows the return to the original state. In practice, when the material is polarized in an electrochemical cell, the change of colour is conelated to the insertion/extrac-tion of small ions H" ", Li" ". This insertion/extraction is monitored by the passage from cathodic to anodic polarization which allows to go from bleached (or coloured) state to coloured (or bleached) one. This property belongs to all (or almost all) transition metal oxides it corresponds to the change of valency of the cation Ni "> Ni " O . .. accompanied... 

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