Salinity gradient power-reverse electrodialysis and alkaline polymer electrolyte water electrolysis for hydrogen production

In this work, innovative use of Salinity Gradient Power (SGP) as renewable energy source for indirect production of hydrogen is addressed. A lab-scale reverse electrodialysis (RED) unit, fed with different NaCl solutions mimicking highly concentrated brine (5M), Reverse Osmosis retentate (1M), seawater (0.5 M) and brackishwater (0.1M), was coupled to an alkaline polymer electrolyte (APE) water electrolysis cell. SGP-RED unit, equipped with 27 cell-pairs, reached at bestan Open Circuit Voltage (OCV) of 3.7 V and maximum gross power density of 3.2 Wm2 MP (membrane pair) when feeding the low concentration compartment (LCC) with 0.1 M NaCl and the High Concentration Compartment (HCC) with 5 M NaCl. The single-cell APE water electrolys isunit, operated at 1.8V, attained a current density of 120 mAcm2 under the following configuration: 10% w/w KOH electrolyte, highly conductive anion selective membrane composed of inert low-density polyethylene, finely milled anion selective particles and water-soluble poly(ethyleneglycol-ran-propyleneglycol), non-Platinum catalysts (NiCo2O4 and NiFe2O4) loading of 10 mgcm2 and 15% w/w polymerbinderatbothcathodeandanode, and operational temperature of 65 °C. The integrated system resulted in a maximum hydrogen production rate of 44 cm3 h1 per cm2 of electrode surface area.