Simultaneous hydrogen generation and wastewater purification: An innovative closed-loop reverse electrodialysis system incorporating air–gap diffusion distillation

Abstract

Air-gap diffusion distillation (AGDD) is a thermal distillation technology that can convert low-grade heat sources into salinity gradient energy, offering broad application potential. Since the AGDD system operates under atmospheric pressure, it can be seamlessly integrated with reverse electrodialysis (RED) technology, facilitating the conversion of low-grade thermal energy into electricity, hydrogen, and chemical energy. This paper constructs, for the first time, an AGDD-RED mathematical model that simultaneously achieves hydrogen generation and wastewater purification. Accordingly, the influence behaviors of the concentration of AGDD feed solution (0.5 mol·L^-1-5 mol·L^-1) and low-grade heat source temperature (55–95 °C) on hydrogen generation performance and degradation efficiency are simulated and discussed. At a feed concentration of 3 M, hydrogen generation and COD degradation rates achieve their peak values of 0.19 kW and 46.4 %, respectively. At 55 °C, the degradation rate and hydrogen generation reach their highest values, at 47.1 % and 0.2 kW, with the total energy conversion efficiency reaching 1.65 %. Finally, the energy distribution of the entire system is analyzed, and the results show that the salinity gradient energy regeneration process in the AGDD subsystem is the key factor affecting the efficiency of the system. Reducing pump power consumption and non-ohmic resistance in the RED subsystem will effectively improve the energy conversion performance of the system.