Journal of Sol-Gel Science and Technology 19, 559–562, 2000 c  2000 Kluwer Academic Publishers. Manufactured in The Netherlands. Hydrogen Gas Sensing of High Electrical Conducting-P 2 O 5 -SiO 2 Glasses Prepared by Sol-Gel Process HIROMI MATSUSHITA, RITSUKO NAGAO, MASAYUKI NOGAMI ∗ , TOSHIHIRO KASUGA AND TOMOKATSU HAYAKAWA Department of Materials Science and Engineering, Nagoya Institute of Technology, Showa Nagoya, 466-8555 Japan nogami@mse.nitech.ac.jp Abstract. High proton-conducting P 2 O 5 -SiO 2 glass was applied to the electrolyte of the hydrogen concentration cell for hydrogen gas sensing. 5P 2 O 5 ·95SiO 2 glass was prepared using the sol-gel method and its electrical con- ductivity and electromotive force were measured at 50 ◦ C as a function of both the ambient humidity and hydrogen gas concentration. The electrical conductivities increased with increasing humidity and reached ∼10 −2 S/cm at 90% relative humidity. The electromotive force of the hydrogen concentration cell, where the glass was used as a membrane, showed good Nernstian response to hydrogen pressure in the high relative humidity region. Keywords: proton conductor, phosphate glass, sol-gel, hydrogen concentration cell 1. Introduction Fast proton-conducting solids have attracted much at- tention because they can be used as electrolytes in fuel cells, hydrogen sensors, etc. Clean energy technology using the proton conducting materials may be a possi- ble solution in the prevention of pollution. A number of fast proton conductors have been discovered dur- ing the past two decades [1–3]. Some of them [4–11] show high conductivities of ∼10 −2 S/cm below 100 ◦ C. However, their chemical durability limits the use in practical applications. On the other hand, fast proton- conducting glasses, if developed, extend beyond the limitation of the above compounds because of their high chemical and mechanical durabilities. Recently, we used a sol-gel method to prepare P 2 O 5 - SiO 2 glasses exhibiting high conductivities at room temperature [12–16]. If these glasses can be used as a sensor, it has many advantages [17]. According to our previous paper [18], the proton conductivities were de- pendent on the pore properties of the samples and the ambient humidity. In this work, the P 2 O 5 -SiO 2 glasses ∗ To whom all correspondence should be addressed. are applied to the hydrogen concentration cell for sens- ing hydrogen gas. We measure the electromotive force as a function of partial pressure of hydrogen gas and relative humidity and discuss the Nernstian response of the electromotive force with respect to the pore prop- erties of the sample. 2. Experimental 5P 2 O 5 ·95SiO 2 (mol%) glasses were synthesized ac- cording to the sol-gel method from tetraethyl or- thosilicate (Si(OC 2 H 5 ) 4 , 99.9%, Colcote, Japan) and trimethyl phosphate (PO(OCH 3 ) 3 , >98%, Nacalai tesque, Japan). Si(OC 2 H 5 ) 4 was first hydrolyzed at room temperature with the mixed solution of H 2 O, C 2 H 5 OH and HCl in molar ratios of 1 : 1 : 0.0027 per mole of Si(OC 2 H 5 ) 4 for 1 h. After adding PO(OCH 3 ) 3 , the solution was further hydrolyzed with the solution of 4H 2 O, 4C 2 H 5 OH, 0.011HCl per mole of the ob- tained alkoxide complex for 1 h. After hydrolyzing, formamide, HCONH 2 , was added, and the solution was stirred for 0.5 h. The amount of HCONH 2 was 1 or 3 mL for 5 g-oxide glass. The resultant sol was left and aged for ∼1 month in an air to form a stiff gel with