Thermo‐Osmotic Energy Conversion Enabled by Covalent‐Organic‐Framework Membranes with Record Output Power Density

• Published in: Angewandte Chemie 2022-04, Vol.134 (18), p.n/a
• Main Authors: Zuo, Xiuhui, Zhu, Changjia, Xian, Weipeng, Meng, Qing‐Wei, Guo, Qing, Zhu, Xincheng, Wang, Sai, Wang, Yeqing, Ma, Shengqian, Sun, Qi
• Format: Article
• Language: English
• Subjects: Charge Density; Chemistry; Covalent Organic Frameworks; Direct conversion; Energy; Energy charge; Energy conversion; Estuaries; Free energy; Gibbs free energy; Ion flux; Low-Grade Energy; Membranes; Osmotic Energy Harvesting; Permselective membranes; Salinity; Salinity effects; Temperature gradients; Thermo-Osmotic Energy Conversion
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202116910

A vast amount of energy can be extracted from the untapped low‐grade heat from sources below 100 °C and the Gibbs free energy from salinity gradients. Therefore, a process for simultaneous and direct conversion of these energies into electricity using permselective membranes was developed in this study. These membranes screen charges of ion flux driven by the combined salinity and temperature gradients to achieve thermo‐osmotic energy conversion. Increasing the charge density in the pore channels enhanced the permselectivity and ion conductance, leading to a larger osmotic voltage and current. A 14‐fold increase in power density was achieved by adjusting the ionic site population of covalent organic framework (COF) membranes. The optimal COF membrane was operated under simulated estuary conditions at a temperature difference of 60 K, which yielded a power density of ≈231 W m−2, placing it among the best performing upscaled membranes. The developed system can pave the way to the utilization of the enormous supply of untapped osmotic power and low‐grade heat energy, indicating the tremendous potential of using COF membranes for energy conversion applications. A process for simultaneous and direct conversion of energy from the low‐gradient heat and salinity differences into electricity was developed using ionic covalent‐organic‐framework membranes. A higher membrane charge density enables greater ion‐transport resistance. The optimal thermo‐osmotic energy conversion device offers a power density of 231 W m−2 with a temperature difference.