Study On The Optimization Of Protective Coating And Composite Process Of Skutterudite Thermoelectric Materials

With the problems of environmental pollution and energy shortage becoming increasingly serious,the society have begun to pay attention to the use of renewable and clean energy,and the government and enterprise increase the investment.In recent years,clean energy such as solar energy,wind energy and tidal energy have gradually entered the energy market.However,in the next few decades,fossil energy such as oil,natural gas and coal will still occupy the main position of the energy market.Therefore,improving the energy conversion efficiency of fossil energy and applying energy-saving and emission reduction technologies such as recycling low-grade waste heat have received much attention.Thermoelectric conversion is a green energy technology that employs the thermoelectric effect of semiconductor materials to directly convert thermal energy and electrical energy.It has great potential in the fields of industrial waste heat recovery,energy conservation and emission reduction,and environmental protection.In this work,n-type Yb_0.3Co₄Sb₁₂ skutterudite with the best thermoelectric performance was selected as the studied object for exploring the cause of material degradation in high temperature and ambient environments.It has been found that at the service temperature,the oxidation of the material and the sublimation of the stibonium element would cause the changes in the chemical composition,which ultimately leads to the deterioration of the thermoelectric properties.Among them,the rate of the deterioration of material conductivity decreases with the aging time,and tends to be stable.That is,the high temperature service in the air leads to the decrease of the conductivity of Yb_0.3Co₄Sb₁₂ skutterudite material over time.After aging at 600°C for 30 days in the air,the electrical conductivity and ZT of the material both were decreased by about 20%.In order to delay the degradation rate of Yb_0.3Co₄Sb₁₂ skutterudite material,an Al-based composite coating was prepared by electrochemical deposition.The research shows that the Al,Al-Ni and Al-Ni-Al coatings all have the effect of suppressing the stibonium element of the skutterudite materials.Among them,Al-Ni and Al-Ni-Al thermally diffuse at the same time as high temperature oxidation,forming an ordered and dense aluminum-nickel intermetallic compound capable of effectively isolating oxygen and suppressing the sublimation of stibonium.The thermoelectric properties of Yb_0.3Co₄Sb₁₂ coated with the surface protective coating were not significantly attenuated after aging for 30 days in air.Considering economy and environmental protection,the Al-Ni protective coating is the optimal protective coating for skutterudite materials.In addition to the protection of the skutterudite materials,this paper further enhances the thermoelectric properties of Yb_0.3Co₄Sb₁₂ skutterudite materials through graphene oxide composites.The results show that the graphene oxide?GO?composite can be inserted into the crystal lattice of the material by coating the grain,thereby reducing the thermal conductivity of the material,and the thermoelectric properties can be improved by optimizing the amount of GO and its distribution.In this paper,the optimal ZT value of the composite material is about 1.4,which is 10%higher than the ZT value of the uncomposite material.