The measurement of state of charge of a lead-acid battery by remotely monitoring H+ ion concentration of the battery electrolyte potentiometrically is much more attractive than the labour intensive method of measuring specific gravity of the electrolyte. Unfortunately, the traditional H+ potentiometric sensors such as the glass electrode cannot be used in the concentrated sulfuric acid battery electrolyte. This paper describes our work on the possibility of using 1,1'-bis(11-mercaptoundecyl)ferrocene Fc(C11SH)(2) for measuring changes in the hydrogen ion concentration with a view to developing a miniaturized battery state of charge determining device. A cyclic voltammetric study of the electrochemical response and chemical stability of the alkanethiol ferrocene derivative redox couple is discussed. It is found that the oxidation peak potential of the investigated ferrocene is independent of pH in the range 2-10. However, in concentrated sulfuric acid media 1-5 M, which is more relevant to the targeted application, the oxidation peak shifts linearly to less positive potentials as a function of the acid concentration. The promise of this observation for determining state of charge of lead-acid batteries is explored.
Issa, T. B., Singh, P., Baker, M., & Verma, B. S. (2001). 1,1'-Bis(11-mercaptoundecyl)ferrocene for potentiometric sensing of H+ ion in sulfuric acid media simulating lead acid battery electrolyte. Journal of Applied Electrochemistry, 31(n/a), 921-924. https://doi.org/10.1023/A:1017569602261