Hydrogen production from industrial wastewaters: An integrated reverse electrodialysis - Water electrolysis energy system

This work presents a novel approach combining reverse electrodialysis (RED) and alkaline polymer electrolyte water electrolysis (APWEL) for renewable hydrogen production. APWEL is fuelled by salinity gradient power (SGP) extracted from sulfate (SO42−)-rich industrial wastewater. The performance of a pilot-scale RED unit (200 cells, active area: 31.5 × 63.5 cm2), using salt solutions mimicking sulfate-rich waste streams (0.01–0.3 M Na2SO4), was evaluated. An open circuit voltage (OCV) of 12.3 V, a maximum power density of 0.22 W/m2MP (MP: membrane pair) and internal area resistance of 43.2 Ωcm2/cell were recorded by using 0.01 M/0.3 M Na2SO4 solutions at 35 °C. The APWEL stack (6 cells, active area: 5 × 5 cm2), equipped with Ni foam electrodes and heterogeneous anion-selective membranes, was tested with varying concentrations of liquid electrolyte (0.85–2.5 M KOH) and varying temperatures (28–48 °C). The APWEL stack attained a maximum current density of 110 mA/m2 at 1.85 V/cell (i.e. 11 V per stack), 2.5 M KOH and 48 °C. Under these conditions, the integrated system exhibited a maximum hydrogen production rate of 50 cm3/h·cm2. This study opens up a new perspective on renewable hydrogen production fuelled by non-intermittent SGP from SO42--rich industrial effluents.