Zinc electrodeposit morphology under conditions of fluctuating current density

A probe has been used to simultaneously measure the electrolyte and particle potentials within a fluidized bed electrode. The difference between the two signals then yielded the overpotential. Transients of all three potentials were stored by a microcomputer and the data processed to yield potential probability distributions and power spectra. Experiments were performed on beds of copper particles undergoing cathodic deposition from acidified sulfate solution and on beds of zinc‐coated particles undergoing deposition or dissolution of zinc with an alkaline zincate electrolyte. Both low frequency and wide band noise were observed in the potentials of copper particles while the former was much less for zinc‐coated polymer particles. An explanation was offered in terms of the hydrodynamics of the electrode, particularly the presence or absence of rising particle‐free regions (“bubbles”). The distributions of time‐averaged potentials with position in the bed were measured and found to be in qualitative agreement with theory. Preliminary results on a moving bed electrode are reported.

Section: Resultssupporting

confidence: 55%

Section: Shibaura Institute Of Technology Assisted In Meeting the Pub...mentioning

confidence: 99%

Electrical and Electrochemical Behavior of Fluidized Bed Electrodes: I . Potential Transients and Time‐Averaged Values

Huh

1987

“…The nature of the effect of copper on bismuth reversibility is not so clear, but it has been already pointed out in the literature 18 that some species can catalyze or inhibit the electrodeposition process. One way in which these species behave as inhibitors is by producing the redissolution of the deposits, consequently leading to substantial transformation of film morphology ͑i.e., avoiding the formation of dendrites or pores͒ and producing a change of the tridimensional growth into a bidimensional one.…”

Section: Resultsmentioning

confidence: 99%

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

Oliveira

Morais

Curvelo

et al. 2003

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...

“…An alternative method for introducing metal oxides into molten salts is to use composite anodes, that is, calcined blocks made from coal tar pitch mixed with metal oxide powder (4)(5)(6)(7)(8)(9)(10). With this approach, oxide solubility in the electrolyte bath is apparently not required.…”

Section: Discussionmentioning

confidence: 99%

Electrical and Electrochemical Behavior of Fluidized Bed Electrodes: II . Effective Bed Resistivities

Huh

1987

Alternating currents were passed through fluidized beds of copper particles and zinc coated polymer particles (Sorapec particles). The sinusoidally varying potential across the bed and that across a known resistor in series with the bed were stored in a microcomputer. In the case of the copper particles the former potential showed amplitude variations thought to be due to voids ("bubbles") within the bed. These amplitude variations were dependent on bed expansion. Beds of Sorapec particles were free of these variations. Effective bed resistivities were determined and found to increase with bed expansion (rapidly in the case of copper particles).