Thermodynamic and efficiency analysis of solar thermochemical water splitting using Ce-Zr mixtures

摘要

We demonstrate the evaluation of the solar-to-fuel conversion efficiency of ceria-zirconia mixtures in a solar thermochemical water splitting system. Energy balance calculations were performed to study the effect of different process conditions on the thermodynamic efficiency of the system. Zirconium-doped ceria showed an enhanced efficiency compared to pure ceria when used in thermochemical water splitting system. A significant enhancement in solar-to-fuel efficiency was shown in case of isothermal redox cycles, at temperature approaches 1800 K with 90% gas heat recovery efficiency, 5% Zr-doped ceria gives an efficiency of 0.032% compared to an efficiency of 0.005% given by pure ceria. However, negative effects were observed upon their use in two-temperature redox cycles at normal oxidation temperatures (900-1200 K). Higher or lower oxidation temperatures resulted in significant enhancement in the conversion efficiency. At oxidation temperature approaching 1600 K and reduction temperature approaching 1773 K with 90% and 80% gas and solid heat recovery efficiency respectively, an efficiency of 0.762% is obtained upon using 5% Zr-doped ceria compared to an efficiency of 0.34% when using pure ceria. At oxidation temperature of 600 K and at the same reduction temperature and heat recovery efficiencies to the previous case, an efficiency of 6.4% is obtained upon using 15% Zr-doped ceria compared to an efficiency of 5.2% when using pure ceria. The optimum conditions for operating a thermochemical water splitting reactor using 5%, 10%, 15% and 20% Zr-doped ceria were investigated and identified. (C) 2016 Elsevier Ltd. All rights reserved.