Solid electrolyte hydrogen sensors

Solid-Electrolyte Hydrogen Sensor. Most of solid gas sensors so far developed need high temperature operation because of limited ionic conductivities when the electrolyte is near room temperature. If solid electrolytes with sufficiently large ionic conductivities are available, unique gas sensors operative near room temperature can be fabricated. An example is the following proton conductor hydrogen sensor proposed by our group (10, 11). 

Katahira, K., Matsumoto, H., Iwahara, H., Koide, K. and Iwamoto, T. (2001) A solid electrolyte hydrogen sensor with an electrochemically-supplied hydrogen standard. Solid State Ionics. 73, 130-4. 

Narayanan, B.K., Akbar, S.A. and Dutta, P.K. (2002) A phosphate-based proton conducting solid electrolyte hydrogen gas sensor. Sens. Actuators B, 87, 480-6. 

PANI/Nb Oj composites have rarely been investigated in the past, e.g., synthesis, characterization, and low-frequency AC conduction of PANI/ Nb Oj composites were reported by Ravikiran et al. [148]. It was recently demonstrated that PANI/Nb Oj-based materials can be used for highly sensitive solid electrolyte gas sensors (e.g., hydrogen, ethene, and propene) up to temperatures of 450°C because of significant thermal stabilization (Figure 2.11) of PANI with Nb O [149]. 

Samec Z, Opekar F, Crijns GJEF (1995) Solid-state hydrogen sensor based on a solid-polymer electrolyte. Electroanalysis 7 1054-1058... 

When analyzing hot gases for their hydrogen snlfide content, for instance, a solid electrolyte sensor consisting of the galvanic cell... 

Electrochemical reaction scheme in a hydrogen sensor with a membrane for gas transport and a solid housing to prevent electrolyte leakage. 

Ramesh, C., Velayutham, G., Murugesan, N., Ganesan, V., Dhathathreyan, K.S. and Perias-wami, G., An improved polymer electrolyte-based amperometric hydrogen sensor, Journal of Solid State Electrochemistry, 7(8), 511, 2003. 

Many - gas sensors based on - solid electrolytes operate under potentiometric conditions [iii]. The sensors for oxygen use oxide -> conductors, such as ZrC>2 -based ceramic, those for halogens use halide conductors (e.g., KAg s), while -> hydrogen sensors use protonic conductors. There are sensors for C02, N02, NH3, S03) H2S, HCN, HF, etc. (see -> lambda probe). 

Maffei, N. and Kuriakose, A.K. (1999) A hydrogen sensor based on a hydrogen ion conducting solid electrolyte. Sens. Actuators B, 56, 243-6. 

FIGURE 2.14 Response/recovery time of the hydrogen sensor based on the (NH4)4Ta,oW03o solid electrolyte (Cj = 10 ppm Cj = 100,000 ppm). (From Zhuiykov, S., Hydrogen sensor based on a new type of proton conductive ceramic, Ira. J. Hydrogen Energy 21 (1996) 749-759. With permission.)... 

Fig. 44. Performance of a hydrogen sensor using a BaCeOs-based ceramic as a solid electrolyte. (Reprinted from Iwahara et al. 1991b by permission of the publisher, The Electrochemical Society Inc.)...

Another interesting application of perovskite-based hydrogen sensors, which has now been commercialized, is for monitoring hydrogen in molten metal such as aluminium, zinc and copper (Yajima and Iwahara 1992). As cerates were not entirely suitable, the investigators used CaZr03 doped with indium oxide as the solid electrolyte (Iwahara 1996). 

The majority of solid electrolyte sensors are based on proton conductors (Miura et al. 1989, Alberti and Casciola 2(X)1). Metal oxides that can potentially meet the requirements for application in solid electrolyte sensors are listed in Table 2.7. These proton condnctors typically do not have high porosity but rather can reach 96-99% of the theoretical density (Jacobs et al. 1993). Similar to oxygen sensors, solid-state electrochemical cells for hydrogen sensing are typically constructed by combining a membrane of solid electrolyte (proton conductor) with a pair of electrodes (electronic conductors) Most of the sensors that use solid electrolytes are operated potentiometrically. The voltage produced is from the concentration dependence of the chenucal potential, which at eqnihbrium is represented by the Nemst equation (Eq. 2.3). 

---