Integrated Electrochemical–Electrolytic Conversion of Oilfield-Produced Water into Hydrogen

This study tackles the challenge of treating high-oil (≥90 mg/L) and high-salinity (Cl− ≥ 6900 mg/L) oilfield-produced water for green hydrogen production. An integrated technology combining electrochemical cascade purification (EDCF: electro-demulsification–coagulation–flotation) with alkaline water electrolysis is developed. The EDCF process effectively reduces oil, suspended solids, and turbidity to <10 mg/L, <20 mg/L, and <20 NTU, respectively, meeting stringent feedwater criteria for electrolysis. An asymmetric electrolysis strategy employing a nickel felt anode/Raney nickel cathode system achieves a low cell voltage of 1.856 V at 1 A/cm2 in 6 M KOH at 85 °C, with 96.58% H2 purity. Crucially, separate anolyte/catholyte (0.5/6 M KOH) mitigates Cl− corrosion, enabling stable 240 h operation (96.66% ± 0.5% H2 purity) in a duplex steel electrolyzer. The work establishes comprehensive boundary conditions for scalable hydrogen production from treated produced water.