Hydrogen generation from seawater via integrated forward osmosis and phosphate buffer electrolysis

• Forward osmosis treatment of seawater is optimised by electrolyte tuning. • Inexpensive electrolyser components are developed for near-neutral H 2 O electrolysis. • Continuous hydrogen generation from seawater at 0.4 A cm −2 is demonstrated. Direct seawater splitting presents a genuinely sustainable pathway to the production of green hydrogen, but is technologically challenging due to interferences from the naturally present solutes in seawater. These challenges can be overcome by coupling forward osmosis and an optimised electrolyser system within an integrated unit, as presented and investigated herein. Through studies of the electrolyte effects, we found that 4 M K x H y PO 4 (pH 8) enables both the effective osmotic uptake of H 2 O from artificial seawater and the electrolysis of H 2 O. We demonstrate that the rates of the electrolyte loss and uptake of the seawater solutes during the forward osmosis using 4 M K x H y PO 4 (pH 8) and a commercial cellulose triacetate membrane are at least 3 orders of magnitude lower than that of the H 2 generation. To facilitate the kinetics of the oxygen and hydrogen evolution reactions, we introduce a hydrogen-templated porous nickel-layer catalyst modified in situ with molybdenum and supported on nickel foam substrate. Combining these relatively inexpensive, non-precious materials within a custom-designed flow-through electrolyser prototype, fed by H 2 O produced by the forwards osmosis from seawater, we demonstrate stable generation of H 2 and O 2 at 0.4 A cm −2 at a cell potential of ca −2.3 V and 90 ± 1 °C across 6 days. Future improvements to the process presented herein might emerge from optimisation of the forward osmosis membrane and gas mass-transport within the electrolyser.