Thermoelectric Properties Of Cement-based Composites Enhanced By Low-content Graphene

Cement-based composites with thermoelectric effect have important application prospects in the fields of urban heat island effect mitigation,low energy snow and ice melting for winter roads,and low-cost scale energy conversion and harvesting.Although great progress has been made in the research of thermoelectric properties of thermoelectric cement-based composites,the high carbon content reduces their mechanical properties significantly and becomes a major obstacle to promote the application of cement-based composites.In this article,by studying the efficient dispersion method of Reduced Graphene Oxide（RGO）to prepare low-content RGO cement-based composites with the combination of RGO surface pretreatment method and metal oxides,it effectively improves the thermoelectric properties of low-content RGO cement-based composites.The microstructure,Seebeck coefficient,electrical conductivity,thermal conductivity,power factor and thermoelectric figure of merit variation of low-content RGO cement-based composites were systematically studied,and the theoretical thermoelectric conversion efficiency of low-content RGO cement-based composites was calculated and characterized.The main studies are as follows.The pre-dispersion process of liquid phase mixing with ethanol was used to make the cement particles directly adhere to the monodisperse RGO flakes,which effectively reduces the RGO interlayer force and improves the dispersion effect and thermoelectric properties of RGO in the matrix of cement-based composites.When the RGO content was 5.0 wt%,the electrical conductivity of the RGO-cement mixed powder prepared by the liquid phase mixing process was as high as 4.56 S/cm,which was much higher than that of the ball milled RGO cement mixed powder with an electrical conductivity of 0.13S/cm.The room temperature thermal conductivity of RGO cement-based composites does not change significantly with the increase of RGO content,which is mainly the result of enhanced phonon scattering due to the increase of RGO-cement interface content.The electrical conductivity and thermoelectric properties of cement-based composites increase with increasing RGO content.When the RGO content was 5.0 wt%,the highest electrical conductivity of the cement-based composites reached 2.01 S/cm,and the maximum ZT value of 0.23×10^-4 was achieved at 65°C,with the average output power and thermoelectric conversion efficiency of 8.27×10^-3 m W/m² and 9.1×10^-7.Study the effects of Cl₂ pretreatment and HNO₃pretreatment on the surface of RGO on the thermoelectric properties of cement-based composites.The results show that the Cl₂ pretreatment and HNO₃ pretreatment increase the RGO defect content,increase the effective mass of carriers and enhanced the Seebeck effect of cement-based composites.the Cl₂ pretreatment on the RGO surface forms C-Cl bonds and the bonding action destroys the RGO conjugate degree,which decreases the RGO electrical conductivity.The chemical adsorption of Cl deflects theπ-electron cloud in RGO and enhances theπ-electron leap,resulting in a certain degree of increase in the electrical conductivity of RGO.When the Cl₂ pretreatment RGO content was 5.0 wt%,the cement-based composite exhibited an N-type semiconductor with a maximum electrical conductivity of 1.54 S/cm,the maximum Seebeck coefficient of-56.61μV/°C,the highest ZT value of 1.08×10^-4,and average output power and thermoelectric conversion efficiencies of 2.91×10^-2m W/m²and 3.79×10^-6.The effects of 5.0 wt%,10.0 wt%and 15.0 wt%metal oxides（CuO,Ni₂O₃ and Ti O₂）on the thermoelectric properties of low-content RGO cement-based composites were investigated.The results showed that with the addition of metal oxides,the thermoelectric properties of low-content RGO cement-based composites were effectively improved.When 5.0 wt%RGO and 15.0 wt%CuO strengthened cement-based composites,the power factor was 0.39μWm^-1K^-2.10.0 wt%Ni₂O₃ strengthened RGO cement-based composites power factor was 0.44μWm^-1K^-2.10.0 wt%Ti O₂ strengthened RGO cement-based composites power factor was 1.23μWm^-1K^-2.Metal oxides strengthened the Seebeck coefficient of RGO cement-based composites,which significantly improve the power factor of cement-based composites.