The spacer characteristic effect on hydrogen and electricity co-generation of a reverse electrodialysis stack driven by the salinity gradient of aqueous potassium acetate solutions

Salinity gradient energy exists between the concentrated and diluted solutions that can be converted to the electromotive force (EMF) to drive power generation and hydrogen production by means of reverse electrodialysis (RED) method. The internal structure optimization is vital to improving the performance of a RED stack. In this study, the influences of spacer material, number of spacers and membranes, and salinity gradient of feed solutions on the output voltage, limiting current, hydrogen production, power density and total power density ratio of the whole system have been experimentally studied. The results show that, the replacement of polyethylene terephthalate spacers by using 316 stainless steel spacers can effectively reduce the internal resistance of the RED stack and indirectly increase the limiting current, output voltage and power density. Further, with the increase of the membrane pairs and metal spacers, the output voltage and limiting current increase correspondingly, but the power density changes along a parabolic path with the maximum value. The concentration increasement on the concentrated feed solution is beneficial to elevate the output voltage, limiting current and power density; however, the input of the extremely concentrated solution decreases the hydrogen and electricity co-generation performance of the whole system.