1,1 '-Bis(11-mercaptoundecyl)ferrocene for potentiometric sensing of H+ ion in sulfuric acid media simulating lead acid battery electrolyte

The measurement of state of charge of a lead-acid battery by remotely monit oring H+ ion concentration of the battery electrolyte potentiometrically is much more attractive than the labour intensive method of measuring specifi c gravity of the electrolyte. Unfortunately, the traditional H+ potentiomet ric sensors such as the glass electrode cannot be used in the concentrated sulfuric acid battery electrolyte. This paper describes our work on the pos sibility of using 1,1'-bis(11-mercaptoundecyl)ferrocene Fc(C11SH)(2) for me asuring changes in the hydrogen ion concentration with a view to developing a miniaturized battery state of charge determining device. A cyclic voltam metric study of the electrochemical response and chemical stability of the alkanethiol ferrocene derivative redox couple is discussed. It is found tha t 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 s hifts linearly to less positive potentials as a function of the acid concen tration. The promise of this observation for determining state of charge of lead-acid batteries is explored.