Preparation And Mechanism Of Bacterial Cellulose-Based Hydrogel Thermocell

With the acceleration of global industrialization,the development and use of non-renewable energy leads to environmental pollution,energy shortage and other problems become increasingly serious.Thermoelectric power generation is a phenomenon of transmission or chemical reaction in thermoelectric materials driven by temperature difference,which provides a new scheme for green,clean and sustainable power generation.However,the low Seebeck coefficient(～μV·K^-1),high cost,and potential toxicity of rare elements have limited the development of thermoelectric generators.Recently,thermocells based on redox reactions have received more attention due to their high Seebeck coefficient(m V·K^-1)and lower production costs,providing a new direction for the development of thermoelectric.In this thesis,bacterial cellulose,which has abundant three-dimensional network structure,high mechanical strength,high liquid load,biocompatibility and can realize large-scale production,is combined with thermoelectric materials.By utilizing chemical reactions within/between materials and ionic interactions,a series of hydrogel thermocells with three-dimensional network structure have been prepared,which have excellent thermoelectric properties,high mechanical properties and temperature sensitivity.The micromorphology,mechanical properties,thermoelectric properties and sensitivity of BC based hydrogel thermocells were analyzed by cryo-scanning electron microscopy,texture analyzer,conductivity test and sensitivity test.The main research contents are as follows:（1）Thermoelectric hydrogels with excellent mechanical properties and large scale production were prepared by using BC as hydrogel matrix and combining K_3/4Fe（CN）₆（p type）and Fe Cl_2/3（n type）thermoelectric materials with BC through simple impregnation process.The Seebeck coefficients of p-type and n-type thermocells are-4.5 m V·K^-1and 0.72 m V·K^-1,respectively,which are much higher than those of thermoelectric generators.The conductivity of p-type and n-type thermocells reached4.9 m S/cm and 68.1 m S/cm,respectively.（2）Porous carbon fiber paper with high specific surface area was introduced into the thermocells to provide a large number of reaction active sites for the thermoelectric materials.On the basis of ensuring the internal chemical reaction of the electrolyte of the thermocell(Fe²⁺（?）Fe³⁺),the chemical reaction between the electrolyte and electrode was promoted(Cu+Fe³⁺→Cu²⁺+Fe²⁺).This synergistic action of BC based hydrogel coupled chemical reaction thermocells has greatly improved the efficiency of thermoelectric power generation.At the temperature difference of 50 K,the Seebeck coefficient of the thermoelectric cell reaches 5.9 m V·K^-1,which is～8 times higher than that of the thermocell without carbon fiber paper.At the same time,the abundant 3D network structure of BC and the high liquid load ensure the continuous power generation of hydrogel thermoelectric cells driven by temperature difference.（3）A flexible organic hydrogel with dual network structure was prepared by free radical polymerization of BC,acrylic acid and glycerol.Then,by simple impregnation process,the thermoelectric materials such as K_3/4Fe（CN）₆and NaCl were introduced to obtain organic hydrogel thermocells.The rich hydrogen bond between the BC hydroxyl group and the carboxyl group of acrylic acid can be generated,and the metal ions can be chelated,which further improves the mechanical properties of hydrogels.The stress of the hydrogel finally reached 1.1 MPa and the strain reached 450%.The synergistic action of glycerol and sodium chloride makes the hydrogel thermocell also have frost resistance and water retention.In addition,the thermocell shows excellent temperature sensitivity.