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

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_xH_yPO₄ (pH 8) enables both the effective osmotic uptake of H₂O from artificial seawater and electrolysis of H₂O. We demonstrate that the rates of electrolyte loss and uptake of the seawater solutes during the forward osmosis using 4 M K_xH_yPO₄ (pH 8) and a commercial cellulose triacetate membrane are at least 3 orders of magnitude lower than that of the H₂ 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 a nickel foam substrate. Combining these relatively inexpensive, non-precious materials within a custom-designed flow-through electrolyser prototype, fed by H₂O produced by the forwards osmosis from seawater, we demonstrate stable generation of H₂ and O₂ at 0.4 A cm⁻² at a cell potential of ca −2.3 V and a temperature of 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.