An N-Type Thermogalvanic Cell with a High Temperature Coefficient Based on the Cu/Cu(en)₂²⁺ Redox Couple

Thermogalvanic cells (TGCs) are at the forefront of effective thermoelectric conversion methods, but the practical utilization of their integrated devices is hindered by the suboptimal performance of N-type TGCs. Herein, a novel redox couple of Cu/Cu(en)₂²⁺ is proposed to construct a liquid-state N-type TGC. The electrochemical reaction involving the Cu electrode, ethylenediamine (en), and their chelated compound Cu(en)₂²⁺ exhibits a significant reaction entropy change, resulting in an enhanced temperature coefficient (α). We reveal that the α of the Cu/Cu(en)₂²⁺-based TGC reaches 1.64 mV K^-1. Furthermore, by optimizing the concentrations of Cu²⁺, ethylenediamine, and (NH₄)₂SO₄ in the electrolyte, both α and normalized power density can be significantly improved, achieving values of 2.12 mV K^-1 and 676 μW m^-2 K^-2, respectively. Moreover, by constructing a P-N junction with P-type and N-type TGC, we achieve a high potential of 121 mV under a temperature gradient of 35 K. This work expands the available redox couple options for N-type TGCs and offers a new pathway for efficient thermoelectric conversion.