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

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.