Thin-layer Temperature-differential Galvanic Cell of Redox Type Using Cytochrome c

Abstract

The use of cytochrome c as a redox couple of redox type temperature-differential galvanic (TDG) cell is based on the fact that the formal potential of cytochrome c is highly dependent on temperature under some conditions. Performance of the thin-layer TDG cell containing cytochrome c and sodium chloride in aqueous solution (Fig.1) was measured in a temperature range of 7-60°C under steady state conditions. The lower temperature was kept at 7°C. Two gold-plate electrodes modified with di(4-pyridyl) disulfide were separated by 1 mm. The emf of the TDG cell changed biphasically (Fig.3) in the same way as the temperature variation of the formal potential of cytchrome c (Fig.2). The measured thermoelectric powers are -0.4--O.5 mV⋅K^-1 at temperatures lower than the inflection points of the emf vs. T curves and -0.7--1.3 mV⋅K^-1 at temperatures higher than those points. The absolute values of these thermoelectric powers are smaller than those of the temperature variation in the formal potential by 0.1-0.5 mV⋅K^-1. Because the diffusion coefficient of cytochrome cis small due to the large size of the molecule, a small output power was obtained with no convection in the electrolyte solution in the cell (Fig.5) a perpendicular gradient in temperature was applied to the cell placed horizontally. When the horizontal temperature gradient was applied to the cell which was placed perpendicularly, natural convection took place in the electrolyte solution. This resulted in greater output power (ca.4 times, Fig.5) with little change in heat flux (Fig.6). The maximum output power, 0.4 m⋅m^-2, was obtained by the cell with 11 mmol⋅dm^-3 cytochrome c and 1 mol⋅dm^-3 NaCl. The results obtained confirmed that the convection played the important role to make high output power and high thermal conversion efficiency for the temperaturedifferential galvanic cell with large molecules.