Preparation And Thermoelectric Performance Of Selenide/Methyl Cellulose Composites

Flexible thermoelectric devices can convert the temperature difference between the human body and external environment into electrical power,which own the advantages of small size and no noise,etc.,and therefore,they can provide the potential solutions for the issue of continuous power supply for wearable devices.However,the performance of flexible thermoelectric materials is still poor,which is difficult to meet the needs of practical applications.The screen printing and solution 3D printing technologies have the advantages of convenient operation,industrial mass production,high degree of freedom in design,and integrated preparation of materials and devices.Therefore,in this thesis,flexible selenide/MC composite thermoelectric films were prepared using the screen printing or solution 3D printing method,and then the cold pressing combined with annealing treatment was applied for the as-prepared composite films.The influences of compositions and microstructures of composite films on their thermoelectric properties were studied.The thermoelectric power generators were fabricated using the as-prepared composite films,and their flexibility and out-put performance were also investigated.The details as below,（1）Copper selenide nanowires（Cu-Se NWs）were synthesized by a wet chemical method,and then the Cu-Se NW/MC composite films were prepared by a screen printing technology,after that the cold pressing combining with annealing process was applied for the composite films.At 380 K,the power factor of the Cu-Se NW/MC composite film reaches a maximum value of 121.87μWm^-1K^-2,corresponding to the electrical conductivity and Seebeck coefficient of 806.11 S/cm and 38.88μV/K,respectively.After bending for 500 times at a radius of 4 mm,the electrical conductivity of the composite film decreased by 6.53%.The output voltage and maximum output power of the flexible thermoelectric generator（f-TEG）with four Cu-Se NW/MC single arms were 0.83 m V and 6.71 n W,respectively,corresponding to a power density of 47.2 m W/m².The resistance change ratio of the f-TEG was less than 4%after bending for 500 times with a radius of 25 mm.（4）（2）Reduced graphene oxide（r GO）/Cu-Se NW composite materials with different content of r GO were synthesized by a wet chemical in-situ growth method,and then the r GO/Cu-Se NW/MC composite films were prepared by a screen printing technology,after that the cold pressing combining with annealing process was applied for the composite films.A power factor of 63.51μWm^-1K^-2 at 300 K was achieved for the r GO/Cu-Se NW/MC composite film with 0.05 wt%r GO.As the measured temperature increased,the electrical conductivity of the composite films decreased,while the Seebeck coefficient increased,as a result,a highest power factor of 117.3μWm^-1K^-2 was obtained for the composite films at 420 K.The maximum output power and power density of the f-TEG with four r GO/Cu-Se NW/MC single arms were10.37 n W and 7.27×10^-2 W/m² at a temperature difference of 11.2 K,respectively.（3）Ag₂Se NWs,poly（3,4-ethylenedioxythiophene）:polystyrenesulfonic acid（PEDOT:PSS,PP）/Ag₂Se NWs,and polyethylene pyrrolidone（PVP）/Ag₂Se NWs were synthesized by a wet chemical method,respectively.The Ag₂Se/MC,PP/Ag₂Se/MC and PVP/Ag₂Se/MC composite films were prepared by a solution 3D printing technology,after that the cold pressing combining with annealing process was applied for the composite films.The introduction of PVP and PP can improve the thermoelectric properties and mechanical flexibility of composite films.A power factor of 1634.37μWm^-1K^-2and 2191.47μWm^-1K^-2 was obtained at 300K and400 K,respectively.After bending for 1000 times at a radius of 4 mm,the resistance change ratio of the PVP/Ag₂Se/MC composite film was less than 5%.A flexible PVP/Ag₂Se/MC thermoelectric generator was directly printed using the 3D printing technology,and a maximum output power and power density of 1735.49 n W and 13.453 W/m² were generated at a temperature difference of 27.7 K.The resistance change ratio of the flexible device is 6.4%after bending for 1000 times at a radius of 12.5 mm,indicating that the printed device has excellent flexibility.