Modulating thermo-diffusion/galvanic coupling via ion speciation engineering enables high-performance ionic thermoelectric cells

Ionic thermoelectric (i-TE) materials have demonstrated a high thermopower in harvesting low-grade heat, emerging as superior candidates for self-powered electronics. However, coupling two i-TE effects in n-type materials is scarce, which restricts the development of high-performance systems. Herein, we uncover an overlooked thermogalvanic redox reaction between Cu2+ and Cu+ stabilized by Cl⁻ and quantitatively track the progressive reaction process by operando characterization. In binary polyvinyl alcohol (PVA)-CuCl2 gels, an interactive i-TE coupling effect driven by ion speciation is validated, which exhibits an enhanced thermogalvanic redox as CuCl2 concentrations increase while suppressing the thermodiffusion contribution. By distinguishing and quantifying coordination species, we reveal the impact of [Cu-Cl] speciation on the i-TE effect contributions. Correspondingly, a giant thermopower of −30.6 mV K-1 and a remarkable power density of 0.6 mW m-2 K-2 are achieved, respectively, by tuning ion coordination speciation. The long-term power generation exhibits a reversible and sustainable heat-to-electricity conversion. High output voltage of 3.5 V and power of 22 µW are produced in 16-cell i-TE modules when harvesting 15 K. Our findings reveal an interactive thermo-diffusion/galvanic coupling effect based on coordination chemistry, offering a potential design principle for high-performance i-TE materials. Coupling two ionic thermoelectric effects in n-type materials is scarce, restricting the development of high-performance systems. Here, the authors present an ionic-thermoelectric material with interactive thermo-diffusion/galvanic coupling effect based on coordination chemistry.