Temperature gradients are generated by the sun and a vast array of technologies and can induce molecular concentration gradients in solutions via thermodiffusion (Soret effect). For ions, this leads to a thermovoltage that is determined by the thermal gradient ΔT across the electrolyte, together with the ionic Seebeck coefficient αi. So far, redox-free electrolytes have not been explored in thermoelectric applications due to a lack of strategy to harvest the energy from the Soret effect. Here, we demonstrate the conversion of heat into stored charge via the ionic Soret effect in an IonicThermoelectric Supercapacitor (ITESC), thus providing a new means to harvest energy from intermittent heat sources. We show that the stored electrical energy of the ITESC is proportional to (ΔTαi) 2 and that its αi reaches beyond 10 mV/K. The resulting ITESC can convert and store several thousand times more energy as compared to a traditional thermoelectric generator connected in series with a supercapacitor. INTRODUCTIONVarious thermoelectric concepts are currently under investigation for conversion of thermal energy into electrical energy, with the goal to provide efficient thermoelectric systems. First, electronic charge carriers in a conductor thermodiffuse when subjected to a temperature gradient, which leads to a thermovoltage known as the Seebeck voltage. Thermoelectric generators (TEGs) that utilize the Seebeck effect are typically composed of semi-metals [1, 2], inorganic semiconductors [3, 4], and electronically conducting polymers have also recently been explored [5]. Secondly, thermovoltages can originate from the thermogalvanic effect, which results from temperature-dependent entropy changes during electron transfer between a redox molecule and an electrode [6]. Hence, thermogalvanic cells are based on electrolytes with redox couples, such as ferricyanide/ferrocyanide. The Soret effect [7] of redox free electrolyte, i.e. from ionic charge carriers constitute yet a third thermoelectric concept that, to the best of our knowledge, has not previously been considered for energy harvesting.Analogous to the electronic Seebeck effect, the Soret effect is a result of thermo-diffusion of ions in an ionic solid [8, 9] or electrolyte [10]. This produces an ionic concentration gradient and a corresponding thermo-voltage that is governed by the temperature difference across the material and the ionic Seebeck coefficient αi.For a traditional thermoelectric leg, composed of a semiconductor and two metal contacts, a constant electrical power can be provided to an external load by imposing a temperature gradient along the metal-semiconductor-metal stack. The same harvesting principle is, however, not directly applicable if the semiconductor is replaced by an electrolyte solution with ions as charge carriers. The reason for this is that the thermo-diffused ions are blocked at the surface of the metal electrode and cannot pass through the external circuit. Instead, the ions will be accumulated in excess at the metal surface where th...

have been reported in inorganic ionic solids [ 15 ] and electrolytes, [ 16,17 ] where ions are the only charge carriers. But to the best of our knowledge, the ionic thermoelectric effect in conducting polymers has not been studied and reported before.Here, we investigate the role of ions in the thermoelectric response of different PEDOT derivatives. We observe surprisingly large increases in the thermo-induced voltage at high humidity levels, of up to several hundreds of µV/K, which is identifi ed as an ionic Seebeck effect. The ionic thermovoltage and its potential for improving the thermoelectric effi ciency in conducting polymers are discussed.Five different PEDOT derivatives of different electrical conductivities (measured at 10% RH, 300 K) are deposited on glass substrates including two gold electrode patterns separated by 1 mm: (i) PEDOT-Tos (thickness = 627 nm, σ = 15 200 S m −1 ) synthesized by using solution oxidative in situ polymerization, [ 18 ] (ii) PEDOT-PSS-DEG (4.75 µm, σ = 530 S m −1 ) obtained by the addition of 2 wt% of the secondary dopant diethylene glycol (DEG) [ 19 ] into the PEDOT-PSS dispersion, (iii) PEDOT-PSS (5.68 µm, σ = 14 S m −1 ) as the commercial water dispersion called Baytron P by H. C. Starck, (iv) PEDOT-PSSPSSNa (3.43 µm, σ = 0.08 S m −1 ) obtained by the addition of 2 wt% of PSSNa to the PEDOT-PSS dispersion, and (v) selfdoped PEDOT-S (116 nm, σ = 75 S m −1 ), in which the sulfonate dopant groups are covalently linked to the PEDOT chains. PEDOT-S has been synthesized in the lab. [ 20 ] PEDOT-Tos exhibits the highest electrical conductivity. PEDOT-Tos possesses a high density of conducting PEDOT chains (EDOT/sulfonate molar ratio is 2.7) packed in a paracrystalline structure. [ 18 ] In PEDOT-Tos, the tosylate moieties are the anions and balance the positive charges carried along the conducting polymer chains. The included ions are effectively immobile in the polymer; it is an electronic (hole) conductor. In PEDOT-S, the EDOT/sulfonate ratio is 1.

Integrated organic electronic analog and digital circuits can be formed within plant parts and live plants.

Durable, electrically conducting yarns are a critical component of electronic textiles (e-textiles). Here, such yarns with exceptional wear and wash resistance are realized through dyeing silk from the silkworm Bombyx mori with the conjugated polymer:polyelectrolyte complex PEDOT:PSS. A high Young’s modulus of approximately 2 GPa combined with a robust and scalable dyeing process results in up to 40 m long yarns that maintain their bulk electrical conductivity of approximately 14 S cm–1 when experiencing repeated bending stress as well as mechanical wear during sewing. Moreover, a high degree of ambient stability is paired with the ability to withstand both machine washing and dry cleaning. For the potential use for e-textile applications to be illustrated, an in-plane thermoelectric module that comprises 26 p-type legs is demonstrated by embroidery of dyed silk yarns onto a piece of felted wool fabric.