Preparation And Thermoelectric Properties Of Cu₂Se/Graphene Nanocomposite By Chemical Method

Nowadays, it has been a worldwide issue to improve the energy efficiency and to develop clean energy in order to effectively promote the sustainable development of economy and environment. As a new kind of environmentally friendly materials, thermoelectric(TE) materials have attracted intensive attention over the past decades, among which Cu2Se-based compounds emerge as a promising candidate with abundant elements and also superior TE performance. Currently, the common methods used for fabricating such compounds involve solid-state reaction and melting-quenching method, which need high temperature or long reaction time and thus increase energy consumption. In addition, the recently developed self-propagating high-temperature synthesis(SHS) for Cu2 Se has been proved to be time efficient and suitable for large-scale production, but it requires high purity elements which boosts the cost. Ascribed to the previous mentioned drawbacks, this study developed a new method to synthesize Cu2 Se compounds aiming to minimize both costs and energy consumption, and utilizing graphene as the composite additive to enchance the elelctrical conductivity. In this research, the possibility, process parameters and formation mechanism of synthesizing Cu2 Se /graphene composites by utilizing a facile and novel low temperature wet chemical method were explored The influence of particle size distribution and graphene content on the thermoelectric properties of composite were explored. The results are presented below:In this study, Cu2Se/graphene composites were synthesized by wet chemical method. For the one-step samples, Cu2 Se particles were distributed on the surface of graphene or half-surrounded by graphene, while for the two-step samples, Cu2 Se particles were uniformly anchored on the surface of graphene. By further analyzing the mechanism, it has shown that both ionic reaction and atomic reaction happened during compositing process, and the addition of graphene prolonged the reaction time, which may be caused by the effect of graphene dispersion on the Cu source and the acidity of graphene.Residual oxygen containing functional groups were removed by heat treatment under reducing atmosphere. Infrared(IR) and Raman results indicate that oxygen containing functional groups were removed completely when treated at 450 ? for 4 h. The particle sizes of resulting composites were measured by mastersizer, which increase with rising reaction temperature and time extension and range from nanoscale to micron level. The densification process of composite powders was conducted by plasma activated sintering(PAS).Particle size of composite powder had a great influence on the thermoelectric properties of the material, the thermal conductivity increase with the particle size.The peak ZT of 1.03 is achieved at 673 K for composite materials with the smallest particle size.The influence of graphene contents on the thermoelectric properties of bulk materials was investigated. The introduction of moderate graphene significantly increases the electrical conductivity and also reduces the thermal conductivity of Cu2Se/graphene composites. However, with further increase of graphene content, the electrical conductivity decreases and thermal conductivity increases. As a result, the peak ZT of 1.34 is achieved at 773 K for Cu2 Se doped with 1% graphene, which is more than twofold improvement over the pure Cu2 Se sample.