Study On Thermoelectric And Photocatalytic Properties Of CdO-based Materials

CdO is a n-type semiconductor with good electrical conductivity,which is very promising in the fields of photoelectricity,thermoelectrics and photocatalysis.In the past few decades,numerous works had been reported on the photoelectric performance of CdO,while researches on its thermoelectric and photocatalytic performances were very limited.In the present work,thermoelectric and photocatalytic properties of CdO polycrystals and nano CdO were studied in detail,and various strategies were adopted to optimize the thermoelectric and photocatalytic performances of CdO-based materials,the main results are listed as below:1)Porous CdO polycrystals can be fabricated using PMMA as the void forming agent.The introduction of micro/nano sized pores drastically reduced the thermal conductivity of CdO-based materials,however,the electrical property was also decreased.Cu was used as the dopant to further optimize the electrical property of porous CdO,which improved its electrical conductivity while maintaining relatively low thermal conductivity.At 823 K,the figure of merit ZT of porous Cd_0.99Cu_0.01O is 63%higher than the dense undpoed CdO.2)Intentionally designed CdO-based hierarchical structure were prepared by doping CdO with alkaline earth metal elements like Mg,Ca,Ba.The scatterings from point defects,nano precipitations and grain boundaries led to a great reduction in the lattice thermal conductivity of CdO-based polycrystals that close to the amorphous limit of CdO.All alkaline earth metal elements doped CdO-based polycrystals showed enhanced thermoelectric performance due to the drastically reduced thermal conductivity,among which Cd_0.94Mg_0.03Ca_0.03O achieved the highest ZT value of 0.5 at 1000 K.3)The electrical property of CdO polycrystals was optimized through band engineering by doping transition metal element Ni.It was found that doping Ni can introduce an impurity band below the conduction band of CdO and resulted in increased band gap,the electrical resistivity and Seebeck coefficient of Cd_1-xNi_xO experienced obvious change with increasing temperature,and the power factor showed large improvement in the whole measured temperature range.At 1000 K,the power factor of Cd_0.99Ni_0.01O reached 1.54×10^-3 W/mK².4)Noble metal Ag was chosen as the nano dispersed phase to construct the CdO:Ag nanocomposites.The carrier energy filtering effect resulted from CdO:Ag interfaces can enhanced the Seebeck coefficient of the composites,and led to improved power factor;while the strong phonon scatterings from Ag nano particles and CdO/Ag interfaces in the composites further suppressed the thermal conductivity.Finally,synergistic optimization of electrical and thermal transport properties was realized in CdO:Ag nanocomposites.5)Using modified half-successive ion layer adsorption and reaction,nano CdO/metal oxide?SnO₂,Fe₂O₃?2D nanosheets heterostructures can be successfully fabricated.CdO had high photosensitivity for visible light and 2D nanosheet had high surface area,which led to excellent photocatalytic activity for prepared heterostructures.Efficient carrier separation and high photocatalytic activity were achieved in CdO/Fe₂O₃ heterostructure due to its band structure,after 40 min of irradiation,70%methylene blue can be degraded.