Thermogalvanic conversion of heat to electricity

Abstract

A thermogalvanic (nonisothermal) cell was constructed for carrying out power conversion efficiency measurements. The design departed from that of traditional thermogalvanic cells which have largely been used only for studies of open-circuit voltage. The cell was used to obtain temperature coefficients, ∂E/∂T, of the open circuit voltage and power conversion efficiencies, Φ, for an interelectrode temperature difference, ΔT, of 20 K, using various redox couples. The values obtained were the following: Cu 2+/Cu (1.0 mol dm −3), ∂E/ ∂T = 785 μV K −1; Zn 2+/Zn (1.0 mol dm −3), ∂E/ ∂T = 790 μV K −1; Fe phen(CN) 4 −/Fe phen(CN) 4 2− (10 −3 mol dm −3), ∂E/ ∂T = 1046 μV K −1, Φ = 4.17 × 10 −5%; Fe(CN) 6 3−/Fe(CN) 6 4− (0.07 mol dm −3), ∂E/ ∂T = 1600 μV K −1, Φ = 1.4 × 10 −2%. More detailed studies of the latter system when [Fe(CN) 6 3−] = [Fe(CN) 6 4−] = 0.26 mol dm −3 and [KCl] = 0.80 mol dm −3, using platinum electrodes, with ΔT = 20 K, gave a current density of 1.45 mA cm −2 and a power conversion efficiency, Φ, of 2.8 × 10 −2%. This approaches 0.5% of the maximum theoretical efficiency of a Carnot engine operating across the same temperature difference.