An Organic Aqueous Gel as Electrolyte for Application in Electrochromic Devices Based in Bismuth Electrodeposition

Abstract

The purpose of this work was to study the deposition/dissolution behavior of bismuth in an aqueous electrolytic gel media from the point of view of electrochromic phenomena. The gel was made from a derivative polymer of animal protein. This polymer is extremely consistent, and it becomes a transparent gel from 350 to 850 nm ͑visible region͒. Moreover, voltammetry and chronoamperometry experiments have shown that the bismuth deposition/dissolution has excellent electrochemical reversibility with a large variation of transmittance values ͑around 60%͒ when Cu 2ϩ is added to the gel. It was also shown that copper cations promote Bi/Bi 3ϩ reversibility by a redox reaction between Cu 2ϩ and metallic bismuth. Thermogravimetric ͑TG͒ and differential scanning calorimetry ͑DSC͒ analysis were used to verify possible changes in the gel when it was exposed to a heating/cooling cycle. From TG analysis it was possible to verify that degradation of the gel polymer in a large temperature range does not occur and from DSC it was observed that the system only freezes at ca. Ϫ35°C.Currently there is great interest in the development of optical devices, mainly those that can control variations of light intensity or heat. There are about 1800 patents that refer to electrochromic devices, about 1500 are from the Japanese industry, but still there are great efforts to produce new devices that can exhibit better properties. Display information devices, 1 automotive applications, 2 and windows, which can control the sunray intensity were the first electrochromic products commercialized.Devices based in metal deposition contain the electrochromic material in the electrolyte that, by the passage of electric current, produce a thin film on the substrate. 3 This device uses the reversible electrodeposition to produce an optical modulation, which does not involve ion insertion, as in the case of WO 3 , and was first proposed by Smith in 1929. 4 Some years later, Camlibel 5 and Zaromb 6-8 related the reversible electrodeposition of silver to optical modulation. Recently, similar devices have been proposed to be used in different aqueous or nonaqueous media; one of these devices based on lead electrodeposition in aqueous media 9 shows a transmittance variation of ca. 60%. The main problem is that a high amount of charge ͑185 mC cm Ϫ2 ͒ is necessary to produce lead electrodeposition in the presence of Cu 2ϩ as additive. Another device uses copper salt in an ammoniac media as an electrochromic electrolyte; the principle of operation of this device is the reduction of Cu 2ϩ to Cu 0 in the transparent cathode while Cu ϩ is oxidized to Cu 2ϩ in the transparent anode. 10 Recent studies with metallic bismuth 11,12 have been done by Ziegler et al., 3 and they have shown a very promising electrochromic device, which is based on the deposition and dissolution properties of metallic bismuth in aqueous media. The device contains Bi 3ϩ and Br Ϫ and small amounts of Cu 2ϩ as an additive. The potential required for the redox process is low, about 1-2 V dc, and...

Dynamic Windows with Neutral Color, High Contrast, and Excellent Durability Using Reversible Metal Electrodeposition

“…In the presence of Cl À and other additives, Cu improves the uniformity of codeposited metals through a mechanism mediated by Cu(I). 26 Although electrodeposition of pure Cu can be conducted with good uniformity, the red color of Cu is undesirable for window applications, and hence we electrodeposit Cu and a second metal in this work. Figure S2).…”

Solid-state electrochromic devices with Nb2O5:Mo thin film and gelatin-based electrolyte

“…This is the case for instance of hydroxyethylcellulose (HEC), modified starch, chitosan or natural rubber [9,10]. The recent results reported using a gelatin-based polymer electrolyte and an electrochemically deposited bismuth layer have attracted our attention and prompted an investigation on the possibility to use gelatin as polymer electrolyte in other all solid-state electrochromic devices [11].…”

Preparation and electrochromic property of covalently bonded WO3/polyvinylimidazole core-shell microspheres

“…They have so far been prepared mostly by dry processes such as vacuum evaporation [5,6] and sputtering [7,8], although wet processes such as electrodeposition [9], the sol-gel method [10,11], and the polymer-encapsulated inorganic particles method [12,13] seem to be more advantageous in producing large-scale films at low cost. Among those methods employed in wet processes, polymer-encapsulated inorganic particles offer many advantages [12][13][14].…”