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...

The effect of thermal resistance, heat leakage and internal irreversibility resulting from the working fluid on the performance of a Carnot heat engine is investigated using a new cyclic model. The power output and efficiency of the heat engine are adopted as objective functions for heat engine optimization. The optimal performance of the heat engine is analysed systematically. Some significant results are obtained. For example, the maximum power output and maximum efficiency are determined. The efficiency of the heat engine at maximum power output and the power output of the heat engine at maximum efficiency are also calculated. Curves of the power output varying with the efficiency of the heat engine are obtained. These curves can indicate clearly the rational regions of efficiency and power output for an irreversible Carnot heat engine. It is pointed out that all the conclusions concerning a reversible Carnot heat engine, an endoreversible Carnot heat engine only affected by thermal resistance and an irreversible Carnot heat engine with internal irreversibility and/or heat leakage can be deduced from the results in this paper.

Amine-functionalized lanthanide-doped KGdF(4) nanocrystals, synthesized via a facile one-step solvothermal route by employing polyethylenimine as the surfactant and capping ligand, have been demonstrated to be sensitive time-resolved FRET bioprobes to detect a trace amount of biomolecules such as avidin at a concentration of 5.5 nM and to be potential T(1)-MRI contrast agents due to a large longitudinal relaxivity of Gd(3+) (5.86 S(-1)·mM(-1) per Gd ion and 3.99 × 10(5) S(-1)·mM(-1) per nanocrystal).