Potentiometric proton-conductor

Fig. 36.1. Dependence of ejnX response of the potentiometric proton conductor sensor on H2 concentration in air and response transient of the sensor to 2000 p.pan. H2 in air at room temperature s (with permission, Kodansha Ltd).

Figure 2 shows the structure of this sensor which is similar to that of the potentiometric sensor reported earlier (10). The only difference is that in this sensor a short circuit current between the sensing electrode and the counter electrode is measured with an ammeter. The proton conductor, antimonic acid (Sb205 2H20), was prepared from antimony trioxide and hydrogen peroxide according to a method described elsewhere (7,14). The sample powder was mixed with... 

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). 

Some proton conductors have relatively high conductivities at room temperature. Introduction of these materials into electrochemical cells brings about attractive chemical sensors workable at room temperature. Potentiometric or amperometric detection of chemical components at room temperature would create new fields of application for sensors especially in bioprocess control and medical diagnosis. With an all-solid-state structure, the sensors would be compatible with micro-fabrication and mass production, and small power consumption associated with their ambient-temperature operation would be intrinsically suited for cordless or portable sensors. 

The probe-type elements (without reference gas) thus obtained are convenient for microminiaturization and integration. In fact, several micro sensors have been fabricated by combining proton conductor films and hydride counter electrodes (PdH or TiH ) their good sensing characteristics have been reported For detection of H2 in air, we have reported a potentiometric element (a) and an amperometric element... 

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). 

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