P–N Conversion in a Water–Ionic Liquid Binary System for Nonredox Thermocapacitive Converters

An intriguing p–n conversion of thermoelectric property was observed in a water–ionic liquid ([EMIm]­[Ac]) binary system with precise control over water content. The highest p-type and n-type Seebeck coefficient were optimized at water–[EMIm]­[Ac] molar ratio of 2:1 and 4:1, respectively. DFT calculation illustrates that a configuration of solvent separation ion pairs is preferred at the water–[EMIm]­[Ac] molar ratio of 4:1, leading to the p–n conversion through weakening interaction between anion clusters and gold electrodes. Furthermore, p–n thermocapacitive converters were integrated to enhance the output Seebeck voltages. This work opens up new perspectives for harvesting low grade heat with the use of fluidic materials.