NOVELTY - A thermoelectric device (100) comprises first electrode (102), second electrode (104), and conducting composition capable of conducting ions, where first and second electrodes are ionically coupled via conducting composition such that applied temperature difference over conducting composition or applied voltage over electrodes facilitates transport of ions to and/or from electrodes via conducting composition, and conducting composition capable of conducting ions comprises polymeric electrolyte.    USE - As thermoelectric device for generating temperature difference and for generating electric current, such as, as temperature sensor or for charging capacitor (all claimed) useful in waste heat management in electricity production (power plants), process industries, transportations or other places where lot of heat is normally lost to surroundings, such as in waste heat management when dealing with waste heat in warm fluids (50-250 degrees C), available in industry, electricity production, buildings and transport; and in renewable power sources such as geothermal or solar heat sources or in combination with solar cells to increase efficiency of solar cells by using heat that is conventionally lost.    ADVANTAGE - The thermoelectric device provides thermoelectric generator for low temperature applications (such as below 200 degrees C) having high thermoelectric figure of merit, can be produced at low cost and is environmentally friendly. The thermoelectric device is based on different principle as compared to prior art devices. While prior art devices are based on electron transport within thermoelectric device, improved thermoelectric device utilizes ion transport or ion transport together with electron transport. The thermoelectric device has high efficiency, low manufacturing costs and printability. Since all functional materials for fabricating thermoelectric device can be solution based, it is feasible to implement thermoelectric devices on flexible substrate by printing or other liquid deposition techniques such as casting. Thus, while prior art devices rely on electron transport in order to obtain thermoelectric effect (Seebeck effect), improved device utilizes ions or ions and electrons as charge carriers. The obtained ionic thermoelectric effect is direct consequence of transport e.g. thermodiffusion, of ions (Soret effect), or ions and electrons, and specific components of constructed devices. In device first electrically conductive polymer composition is capable of being reversibly reduced, and second electrically conductive polymer composition is capable of being reversibly oxidized, or vice versa. This is advantageous as it enables to produce electrical power when submitted to temperature gradient (equivalent to charging battery) and to produce electrical power when no temperature gradient is applied anymore (equivalent to discharging battery). Hence, device can be used advantageously with alternative heat sources (e.g. sun with days and nights), and can provide more constant electrical power versus time in case of alternative heat source and respond better demand of human activities. The possibility to alternately generate electric current, and generate temperature difference i.e. equivalent to battery discharge leads to Peltier effect. The polyelectrolyte facilitates prevention of that both cations and anions move in same leg. By using negatively charged polymer in first leg, cation transport is facilitated, and use of positively charged polymer in second leg results in enhanced anion transport. The advantage of using polyelectrolyte is ability to process it starting from solution. Hence, low cost manufacturing technique such as printing can be used, and further wire-bar coating, knife coating, bar coating, spin coating, dip coating or spray coating, which allows for short manufacturing times. The device includes ion reservoirs comprising mobile ions. It is advantageous to use ionic reservoirs since it ensures good ionic conductivity in electrolyte, such as in polyelectrolyte legs. Further, use of ionic reservoirs prevents any shortage of mobile ions. The addition of reservoir at or integrated with each of electrodes permits more ions to flow through polyelectrolyte legs. Lack of ion reservoir, may result in short life-time of device as continuous transport of ions is necessary for production of continuous electric current. By using ion reservoirs reduction and oxidation on respective electrode can be ensured.    DETAILED DESCRIPTION - A thermoelectric device (100) comprises first electrode (102), second electrode (104), and conducting composition capable of conducting ions, where first and second electrodes are ionically coupled via conducting composition such that applied temperature difference over conducting composition or applied voltage over electrodes facilitates transport of ions to and/or from electrodes via conducting composition, and conducting composition capable of conducting ions comprises polymeric electrolyte. The conducting composition is further capable of conducting electrons. The first and second electrodes comprise material having specific capacitance of 10-1000 F/g, such as material having specific surface area of 50-5000 m2/g or electrically conductive polymer composition capable of being reduced and/or oxidized. The thermoelectric device further comprises at least one ion reservoir (106, 107) at junction between conducting composition and first and/or second electrodes. INDEPENDENT CLAIMS are included for the following:    (1) method for generating electric current involving: providing the thermoelectric device, and applying temperature difference over conducting composition;    (2) method for generating temperature difference involving: providing the thermoelectric device, and applying potential difference between electrodes; and    (3) use of polymeric composition capable of conducting both ions and electrons in thermoelectric device.    DESCRIPTION OF DRAWING(S) - The figure shows schematic drawing of the thermoelectric generator.    Thermoelectric generator/device (100)    First leg (101)    First electrode (102)    Second leg (103)    Second electrode (104)    Connector (105)    Ion reservoirs (106, 107)