The electrochemical Peltier effect observed with electrode reactions of Fe(II)/Fe(III) redox couples at a gold electrode

Abstract

The electrochemical Peltier effect was studied at a gold electrode in solutions containing some Fe(II)/Fe(III) redox couples by measuring the local temperature change in the electrode/solution interphase under controlled-potential and controlled-current polarization. Relative values of the electrochemical Peltier coefficient for the cathodic process at equilibrium potential, which is denoted by (Π c) I=0 , were determined by analyzing the observed temperature change as a function of current. The values of (Π c) I=0 were found to be positive for the Fe(H 2O) 6 2+/Fe(H 2O) 6 3+ systems in HClO 4 (1 M), HNO 3 (1 M), H 2SO 4 (0.5 M), and HCl (1 M), their magnitudes being very similar in the first three acid solutions, but smaller in the HCl solution. On the other hand, a negative value of (Π c) I=0 was obtained in the case of a Fe(CN) 6 4−/Fe(CN) 6 3− couple in a H 2SO 4 (0.5 M) solution. Such a difference in the Peltier coefficient is considered to be due to the difference in the ionic species of iron involved in the electrode reaction.