A Closed-Loop Hydrogen Carrier Ecosystem: From Ocean Desalination to Vehicle Propulsion via a Recyclable Boron–Nitrogen–Carbon Liquid Fuel

This paper presents the complete system architecture of the Ocean-to-Drive-Shaft (OTD) Pipeline — a closed-loop hydrogen carrier ecosystem that converts ocean water into a pumpable, non-volatile liquid fuel using renewable energy, distributes it through existing petroleum infrastructure, extracts hydrogen on-board at just 80 °C using waste heat, and recovers the spent carrier for indefinite reuse. The system employs a novel boron–nitrogen–carbon (B–N–C) ionic liquid carrier (MMG-GBBA, gravimetric capacity 10.27 wt% H₂) whose zero vapor pressure, non-toxicity, and low dehydrogenation temperature eliminate the thermal penalty, volatility, and safety concerns of conventional liquid organic hydrogen carriers (LOHCs). Coastal hub facilities perform solar-thermal seawater desalination and renewable electrolysis to produce green hydrogen, while simultaneously valorizing desalination brine and selling electrolysis-derived oxygen (~8 kg O₂ per kg H₂) as co-products. Distributed inland synthesizer plants regenerate spent fuel using on-site electrolysis of pure water. The on-board catalytic reactor requires only 9.0 kW of thermal duty, fully supplied by fuel cell waste heat (3% of available 300 kW), achieving a round-trip efficiency of ~92%. The delivered hydrogen cost is estimated at USD 1.80/kg H₂.