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Article

Theoretical Thermodynamic Efficiency Limit of Isothermal Solar Fuel Generation from H2O/CO2 Splitting in Membrane Reactors

1
MOE Key Laboratory of Hydrodynamic Machinery Transients, School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, China
2
Department of Chemical System Engineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
3
School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China
4
School of Energy and Environment, City University of Hong Kong, Hong Kong, China
5
Institute of Engineering Thermophysics, Chinese Academy of Sciences, 11 Beisihuanxi Rd., Beijing 100190, China
6
College of Marine Equipment and Mechanical Engineering, Jimei University, Xiamen 361021, China
7
Fujian Province Key Laboratory of Energy Cleaning Utilization and Development, Xiamen 361021, China
*
Authors to whom correspondence should be addressed.
These authors contributed equally to this work.
Academic Editor: Shijun Liao
Molecules 2021, 26(22), 7047; https://doi.org/10.3390/molecules26227047
Received: 21 October 2021 / Revised: 14 November 2021 / Accepted: 19 November 2021 / Published: 22 November 2021
Solar fuel generation from thermochemical H2O or CO2 splitting is a promising and attractive approach for harvesting fuel without CO2 emissions. Yet, low conversion and high reaction temperature restrict its application. One method of increasing conversion at a lower temperature is to implement oxygen permeable membranes (OPM) into a membrane reactor configuration. This allows for the selective separation of generated oxygen and causes a forward shift in the equilibrium of H2O or CO2 splitting reactions. In this research, solar-driven fuel production via H2O or CO2 splitting with an OPM reactor is modeled in isothermal operation, with an emphasis on the calculation of the theoretical thermodynamic efficiency of the system. In addition to the energy required for the high temperature of the reaction, the energy required for maintaining low oxygen permeate pressure for oxygen removal has a large influence on the overall thermodynamic efficiency. The theoretical first-law thermodynamic efficiency is calculated using separation exergy, an electrochemical O2 pump, and a vacuum pump, which shows a maximum efficiency of 63.8%, 61.7%, and 8.00% for H2O splitting, respectively, and 63.6%, 61.5%, and 16.7% for CO2 splitting, respectively, in a temperature range of 800 °C to 2000 °C. The theoretical second-law thermodynamic efficiency is 55.7% and 65.7% for both H2O splitting and CO2 splitting at 2000 °C. An efficient O2 separation method is extremely crucial to achieve high thermodynamic efficiency, especially in the separation efficiency range of 0–20% and in relatively low reaction temperatures. This research is also applicable in other isothermal H2O or CO2 splitting systems (e.g., chemical cycling) due to similar thermodynamics. View Full-Text
Keywords: solar fuel; hydrogen generation; CO2 splitting; H2O splitting; CO generation; membrane reactor solar fuel; hydrogen generation; CO2 splitting; H2O splitting; CO generation; membrane reactor
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MDPI and ACS Style

Wang, H.; Kong, H.; Wang, J.; Liu, M.; Su, B.; Lundin, S.-T.B. Theoretical Thermodynamic Efficiency Limit of Isothermal Solar Fuel Generation from H2O/CO2 Splitting in Membrane Reactors. Molecules 2021, 26, 7047. https://doi.org/10.3390/molecules26227047

AMA Style

Wang H, Kong H, Wang J, Liu M, Su B, Lundin S-TB. Theoretical Thermodynamic Efficiency Limit of Isothermal Solar Fuel Generation from H2O/CO2 Splitting in Membrane Reactors. Molecules. 2021; 26(22):7047. https://doi.org/10.3390/molecules26227047

Chicago/Turabian Style

Wang, Hongsheng, Hui Kong, Jian Wang, Mingkai Liu, Bosheng Su, and Sean-Thomas B. Lundin. 2021. "Theoretical Thermodynamic Efficiency Limit of Isothermal Solar Fuel Generation from H2O/CO2 Splitting in Membrane Reactors" Molecules 26, no. 22: 7047. https://doi.org/10.3390/molecules26227047

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