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Platinum Doped Transition Metal Oxide Electrochromic Display

IP.com Disclosure Number: IPCOM000085941D
Original Publication Date: 1976-Jun-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 26K

Publishing Venue

IBM

Related People

Chang, IF: AUTHOR

Abstract

An electrochromic display device using platinum doped WO(3) as the electrochromic layer promises faster speed and better electrocoloration efficiency which is particularly important for battery operated electrochromic devices, such as watch displays and portable instrument displays.

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Platinum Doped Transition Metal Oxide Electrochromic Display

An electrochromic display device using platinum doped WO(3) as the electrochromic layer promises faster speed and better electrocoloration efficiency which is particularly important for battery operated electrochromic devices, such as watch displays and portable instrument displays.

It has been reasonably established [1] that hydrogen plays an important role in the electrochromic effect of WO(3) films. The reaction may be described by: WO(3) + xH/+/ + xe --> WO(3-x). (OH)(x) or (WO(3) + xH) --> H(x)WO(3) (1)

The reaction speed is mainly limited by the availability of hydrogen ions. The speed of the WO(3) electrochromic effect has been a limiting factor for some display applications. Furthermore, in carrying out the above reaction with reasonable speed, an overvoltage is often necessary, which overvoltage causes a side reaction that reduces the electrochromic efficiency. 2H/+/ + 2e --> H(2) (2)

It has been shown by Hobbs and Tseung [2], that when Pt is admixed with WO(3),it undergoes an apparent enhancement in its ability to catalyze the anodic oxidation of hydrogen in an acid solution. WO(3) alone has no activity towards H(2) oxidation. The reactions are described as: 2H/+/ + 2e + Pt --> Pt(H(2))(gas) --> 2Pt(H) (absorbed atom) (3) Pt + H(2) --> 2Pt(H)(ads) (4) Pt(H)(ads) + WO(3) - -> Pt + H(x)WO(3) (blue) (5)

By adding a small amount of Pt in an electrochromic WO(3) film, the above- described reactions (3) and (5) can be incorporated in the overall electrochromic effect represented by equation (1). The electrochromic efficiency, and therefore speed, is enhanced. The reason for this will be clear when it is understood that Pt serves as a catalyst in promoting the electrochromic reaction (1) by making hydrogen more available to WO(3) (the overvoltage for hydrogen reduction is much lower for Pt). In this regard, platinum has the ability to adsorb hydrogen gas and dissociate it into atoms (see Eq. (3) and (4)).

Because of this ability, any side reaction, like equation (2), due to high voltage applied to the usual electrochromic electrode can be converted to an electrochromic reaction via equations (3), (4) and (5). Therefore, the electrochromic efficiency (amount of optical density obtained per given amount of applied charge) is improved. Better efficiency, then, can afford higher speed.

Figs. 1 and 2 show, by way of example, two Pt doped transition metal oxide (such as WO(3)) electrochromic display de...