Abstract: Based on the general Nernst equation, thermodynamics model of the submonolayer equilibrium potential was set up. Both the underpotential-coverage and the underpotential-electrosorption valency relationships were analyzed, and the interactional properties between the deposit and substrate were obtained. By mean of the theoretical model, the thermodynamic properties of underpotential deposition of Bi-Te compound were obtained. The mechanism of variation of work function with UPD coverage was elucidated via analyzing the system of Bi UPD on several different substrates. The coverage and underpotential of UPD Bi as a function of Bi ion concentration were studied. The results show that the electrosorption valency remains invariant over all underpotential range for Bi UPD in Pt system. However, for Bi UPD in Te-covered Pt system, the electrosorption valency decreases with increasing the Bi coverage. These features will be helpful to explain theoretically the negative shift of Bi UPD on Te-covered substrate.

Key words: Underpotential deposition, Thermodynamics, Thermoelectric materials, Bi-Te substrate system