Elsevier

Materials Letters

Volume 56, Issues 1–2, September 2002, Pages 19-23
Materials Letters

Preparation and proton-conductibility of silica gel containing 64 wt.% undecatungstocobaltoaluminic heteropoly acid

https://doi.org/10.1016/S0167-577X(02)00409-3Get rights and content

Abstract

Silica gel containing 64 wt.% undecatungstocobaltoaluminic acid was prepared by means of sol–gel method. Scanning electron microscope (SEM) and infrared (IR) spectrum revealed that the Keggin structure characteristic of [Al(H2O)CoW11O39]7− anion was present in the silica gel skeleton. The change of the characteristic peaks in the infrared spectrum was investigated. Thermogravimetry (TG) curve shows that there are three steps of weight loss. Differential thermal analysis (DTA) curve shows that the thermal stability of the gel is lower than that of pure undecatungstocobaltoaluminic acid. The silica gel exhibits considerably high proton conductivity of 1.30×10−3 S cm−1 at room temperature (14 °C).

Introduction

Heteropoly acids (HPA) are of special interest as new materials because of their high proton conductivity at room temperature. The conductivity results have been reproduced frequently and these materials have been suggested for applications in hydrogen–oxygen fuel cells, electrochromic devices, and sensors, etc. [1].

The sol–gel syntheses offer new possibilities in the field of solid state ionics by increasing the stability and conductivity of various inorganic materials on gel matrices. The gel materials prepared using the sol–gel method, which are evidently “solid”, contains a large number of micropores and mesopores filled with “liquid” which can be utilized for fast proton transport. A large number of silanol (Si–OH) groups present in the gel skeleton may also be desirable for designing excellent proton conductor composed of silica gels as a host material and appropriate proton conductors as a guest material [2], [3].

The silica gels containing some kinds of heteropoly acid such as 12-molybdophosphoric acid and 12-tungstophosphoric acid have been almost thoroughly investigated. However, few works have been investigated on silica gels containing ternary heteropoly acid. In the present paper, the preparation of silica gel containing 64 wt.% undecatungstocobaltoaluminic acid by means of sol–gel method is reported.

Section snippets

Synthesis

The undecatungstocobaltoaluminic acid H7[Al(H2O)CoW11O39]·14H2O prepared according to the literature [4], i.e. 36.3 g (0.11 mol) of Na2WO4·2H2O, was dissolved in 200 ml of water and the pH of the solution was adjusted to 6.3 with acetic acid. The solution was then heated to boiling and a solution of 2.5 g (0.01 mol) of (CH3COO)2Co·4H2O in 30 ml of hot water was added dropwise with stirring. After 30 min, a solution of 3.8 g (0.01 mol) Al(NO3)2·9H2O in 50 ml of water was added. The pH was

Preparation of silica gel containing undecatungstocobaltoaluminic acid

A hydrolysis catalyst like HCl or HNO3 is usually used in the preparation of silica gels. However, we found that no catalyst was required in the preparation of silica gel containing 64 wt.% undecatungstocobaltoaluminic acid, probably because undecatungstocobaltoaluminic acid can work as a hydrolysis catalyst. Between silica gel containing undecatungstocobaltoaluminic acid with catalysts and without catalysts, there was no marked difference in gelation time, appearance of gel, etc.

SEM

Fig. 1 shows

Conclusion

Silica gel containing undecatungstocobaltoaluminic acid was prepared by means of the sol–gel method. Its IR spectrum and XRD pattern confirm the existence of Keggin anions in the silica gel. The change of the characteristic peaks in the infrared spectrum was investigated. TG curve shows that there are three steps of weight loss. DTA curve shows that the thermal stability of gel is lower than that of pure undecatungstocobaltoaluminic acid. The silica gel containing 64 wt.%

Acknowledgements

We greatly appreciated the financial supports from the Science Foundation of Zhejiang University and China Postdoctoral Science Foundation.

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