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

Abstract

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 (0.5M) and brackish water (0.1M), was coupled to an alkaline polymer electrolyte (APE) water electrolysis cell. SGP-RED unit, equipped with 27 cell-pairs, reached at best an Open Circuit Voltage (OCV) of 3.7V and maximum gross power density of 3.2Wm−2MP (membrane pair) when feeding the low concentration compartment (LCC) with 0.1M NaCl and the High Concentration Compartment (HCC) with 5M NaCl. The single-cell APE water electrolysis unit, operated at 1.8V, attained a current density of 120mAcm−2 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 (ethylene glycol-ran-propylene glycol), non-Platinum catalysts (NiCo2O4 and NiFe2O4) loading of 10mgcm−2 and 15%w/w polymer binder at both cathode and anode, and operational temperature of 65°C. The integrated system resulted in a maximum hydrogen production rate of 44cm3h−1percm2 of electrode surface area.