An electrochemical thermometer: voltammetric measurement of temperature and its application to amperometric gas sensing.

We report a temperature sensing system incorporated into an amperometric oxygen sensor. In the first part of this work, we introduce temperature sensing systems based upon voltammetric responses of both single molecule (1,2-diferrocenylethylene in 1-propyl-3-methylimidazolium bistrifluoromethylsulfonylimide) and two independent molecules (decamethylferrocene and N,N,N',N'-tetramethyl-p-phenylenediamine in 1-ethyl-3-methylimidazolium tetracyanoborate) respectively. In both systems, the difference in the formal potentials of two redox centres was measured as a function of temperature. The former was recorded as the peak difference in square wave voltammetry with the peak potential difference increases linearly with the increasing temperature. In order to show proof-of-concept in relation to a gas sensor, the latter system was investigated in the presence of oxygen, where the concentration and diffusion coefficient of oxygen varied with temperature, as well as the peak difference discussed previously, were studied in the presence of pure oxygen and dried air using chronoamperometry. A negligible variation of concentration of oxygen from both sources with temperature over the range 298 K to 318 K is demonstrated. These results obtained from pure oxygen and dried air were compared and a ca. 79% drop of cathodic signal from pure oxygen to dried air was found which is consistent with the percentage of oxygen in air. The diffusion coefficient of oxygen was related to temperature using an Arrhenius plot (natural log of diffusion coefficient as a function of reciprocal temperature), yielding a linear graph with high correlation. All experiments gave a high reproducibility.