Low-grade heat (below 373 K) is abundant and ubiquitous, but mostly wasted due to the lack of cost-effective recovery technologies. The liquid-state thermocell (LTC), an inexpensive and scalable thermoelectric device, may be commercially viable for harvesting low-grade heat energy if its Carnot-relative efficiency (ηr) reaches ~5%, which is a challenging metric to achieve experimentally. We used a thermosensitive crystallization and dissolution process to induce persistent concentration gradient of redox ions, a highly enhanced Seebeck coefficient (~3.73 mV K–1), and suppressed thermal conductivity in LTCs. As a result, we achieved a high ηr of 11% for LTCs near room temperature, and a substantially decreased cost-performance of our LTC. Our device demonstration offers promise for cost-effective low-grade heat harvesting.

Thermogalvanic cells offer a cheap, flexible and scalable route for directly converting heat into electricity. However, achieving a high output voltage and power performance simultaneously from low-grade thermal energy remains challenging. Here, we introduce strong chaotropic cations (guanidinium) and highly soluble amide derivatives (urea) into aqueous ferri/ferrocyanide ([Fe(CN)6]4−/[Fe(CN)6]3−) electrolytes to significantly boost their thermopowers. The corresponding Seebeck coefficient and temperature-insensitive power density simultaneously increase from 1.4 to 4.2 mV K−1 and from 0.4 to 1.1 mW K−2 m−2, respectively. The results reveal that guanidinium and urea synergistically enlarge the entropy difference of the redox couple and significantly increase the Seebeck effect. As a demonstration, we design a prototype module that generates a high open-circuit voltage of 3.4 V at a small temperature difference of 18 K. This thermogalvanic cell system, which features high Seebeck coefficient and low cost, holds promise for the efficient harvest of low-grade thermal energy.

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We report a bio-inspired ionic skin with high stretchability (>1700%), transparency (>80%) and sensitivity (2 kPa−1).

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High-quality, uniform, one-dimensional (1D) lanthanum hexaboride (LaB 6 ) nanostructures with different morphologies (for example, sparse or dense nanoneedles, or nanorods and nanowire arrays) were fabricated through an effective, easily controlled, one-step, catalyst-free chemical vapor deposition process. The morphologies, structures and temperature-dependent field emission (FE) properties were systematically investigated. FE measurements at room temperature (RT) showed that LaB 6 nanowire arrays possess the best FE characteristics among all 1D LaB 6 nanostructures, with a low turn-on electric field (E to , 1.82 V lm À1 ), a low threshold electric field (E thr , 2.48 V lm À1 ), a high current (5.66 mA cm À2 at 2.92 V lm À1 ) and good stability (at a testing time of 1000 min, fluctuations were o6.0%). Temperature-dependent FE showed that the turn-on and threshold electric fields decreased from 1.82 to 1.06 and 2.48 to 1.62 V lm À1 , respectively, whereas the emission current density increased significantly from 0.20 to 9.05 mA cm À2 at 2.20 V lm À1 when the temperature was increased from RT to 723 K. The emission current density and the dependence of the effective work function on temperature were also investigated. We attribute the significant reduction of the turn-on and threshold fields and the remarkable increase of emission current to a decrease in the effective work function with temperature.