Hydrogen production from water electrolysis driven by the membrane voltage of a closed-loop reverse electrodialysis system integrating air-gap diffusion distillation technology

Abstract

Air-gap diffusion distillation (AGDD) technology is one of attracting desalination technology, which can be used to convert various of low and medium grade thermal energies to the salinity gradient energy (SGE) between two electrolyte solutions at different saline concentrations. The SGE is harvestable and converted to the electromotive force of a reverse electrodialysis (RED) stack. The accumulated voltage by several repeated RED units is capable to driving the electricity or hydrogen production apparatus. This paper proposes the complete mathematical model of a RED-AGDD integration system that converts the low-grade thermal energies (LGTE) to hydrogen driven by the membrane voltage sourced from the salinity gradient of KAc solutions for the first time. Accordingly, the influence behaviors of the concentration of concentrated solution (1 mol L−1 to 7 mol L−1), concentration of diluted solution (0.001 mol L−1 to 0.22 mol L−1), solution flow rate of (0.2 cm s−1 to 1.6 cm s−1), solution temperature (303.15 K to 333.15 K), and hydrogen production schemes (three cases) on hydrogen production performances are simulated and discussed. The hydrogen production and energy efficiency are achieved to be 3.7 L h−1and 0.84% respectively. It verifies that the direct scheme of hydrogen production possesses the better performance than that of the indirect scheme, and an intermediate battery is applied to improve the performance. Finally, the optimal operating conditions and parameters are obtained and presented.