Programmable Electrochemical Thermopower via Cation Storage Mode and Structural Order

This work aims to decouple and quantify the origins of thermopower ( α ) by controlling structure and charge‐storage mechanisms within a single anatase TiO 2 chemistry. Li + and Na + were inserted into anatase TiO 2 particles with sizes of 30 and 5 nm to construct three model electrodes: a bulk crystalline intercalation electrode (30 nm, Li), a nanoscale intercalation and electrical double‐layer (EDL) hybrid electrode (5 nm, Li), and a Na‐induced amorphous, surface‐dominated electrode (5 nm, Na). The 30 nm Li x TiO 2 electrode shows an almost constant α of −1.5 to −1.6 mV K −1 in the biphasic region, corresponding to behavior dominated by lattice‐intercalation entropy. In contrast, amorphous Na x TiO 2 shows α = −4.8 mV K −1 at 0% degree of sodiation and saturates near −2.0 mV K −1 with sodiation, indicating that structural disorder and interfacial entropy strongly enhance, | α |. The 5 nm Li x TiO 2 electrode shows a continuous change in from + 2.19 to −1.6 mV K −1 and acts as an intermediate design point that combines and weights Faradaic and EDL contributions. These results demonstrate that α Faradaic and α EDL can be independently designed within a single anatase TiO 2 material system, providing a platform for electrochemical thermocells with thermopower of several mV K −1 .