Efficient photo-thermo-electric conversion using polyoxovanadate in ionic liquid for low-grade heat utilization

A large fraction of energy, including solar energy, is dissipated into ambient atmosphere as low-grade waste heat. Efficient utilization of such energy is critical to address current energy crisis and global warming issue. Herein, we report the efficient NIR-photothermal, thermoelectric and thus photo-thermo-electric conversion of polyoxovanadate compound ([Ni(1,10-phenanthroline)3][V14O34Cl]Cl, NiV14) in ionic liquid. The solution displays a NIR-photothermal efficiency of 16.04% and 23.43% at 808 and 1064 nm, respectively. Taking advantage of the synergetic thermodiffusive and thermogalvanic effects of various ions species in NiV14 solution, we achieve an open circuit voltage of ca. 0.45 V at ∆T = 70 K generated by physical heating or NIR irradiation, indicating a large Seebeck coefficient of 6.38 mV K-1 and an optimized thermal power at 1.2 W m-2. Polyoxovanadate-ionic liquid system offers a new platform for efficiently utilizing not only low-grade thermal energy but also solar energy for electricity generation.