Energy Conversion Efficiency Enhancement of Polyethylene Glycol and a SiO 2 Composite Doped with Ni, Co, Zn, and Sc Oxides.

Doping the SiO 2 support with Co, Ni, Zn, and Sc improves the thermal conductivity of a hybrid PEG/SiO 2 form-stable phase change material (PCM). Doping also improves the energy utilization efficiency and speeds up the charging and discharging rates. The thermal, chemical, and hydrothermal stability of the PEG/Zn-SiO 2 and PEG/Sc-SiO 2 hybrid materials is better than that of the other doped materials. The phase change enthalpy of PEG/Zn-SiO 2 is 147.6 J/g lower than that of PEG/Sc-SiO 2 , while the thermal conductivity is 40% higher. The phase change enthalpy of 155.8 J/g of PEG/Sc-SiO 2 PCM is very close to that of the parent PEG. PEG/Sc-SiO 2 also demonstrates excellent thermal stability when subjected to 200 consecutive heating-cooling cycles and outstanding hydrothermal stability when examined under a stream at 120 °C for 2 h. The supercooling of the PEG/Sc-SiO 2 system is the lowest among the tested materials. In addition, the developed PCM composite has a high energy storage capacity and high thermal energy storage/release rates.