High‐Performance SiO ₂ Nanoparticle Ionogels for Continuous Heat‐To‐Electricity Conversion

Abstract Ionic thermoelectric (TE) materials recently emerged as the next‐generation TE materials mainly owing to their high thermopower. A big challenge for them is the continuous heat‐to‐electricity conversion because ions cannot transport across the electrodes to external circuit. Here, ionogels using SiO ₂ nanoparticles as the gelator are reported, which enable continuous heat harvesting into electricity under a steady temperature gradient. The ionogels consist of 1‐ethyl‐3‐methylimidazolium dicyanamide (EMIM:DCA), SiO ₂ nanoparticles, polyethylene glycol (PEG), and sodium dicyanamide (Na:DCA). These ionogels exhibit outstanding thermopower and ionic conductivity because both PEG and Na ⁺ ions can retard DCA ⁻ anion transport, while SiO ₂ nanoparticles provide ion conduction channels. They can achieve a high thermopower of 35 mV K ⁻¹ and a high ionic conductivity of 27 mS cm ⁻¹ at room temperature. Interestingly, the ionogels can generate a stable output voltage on the external load under a steady temperature gradient, strikingly different from the control ionogels without SiO ₂ nanoparticles. This TE behavior is similar to that of conventional TE generators (TEGs). The continuous electricity generation can be attributed to the synergistic effects of the charge tunneling across the SiO ₂ nanoparticles and the Soret effect of the ions under temperature gradient.