Comparative System-Level Feasibility Assessment of Onboard Ammonia Electrolysis to Hydrogen Conversion for PEM Fuel Cell Heavy-Duty Trucks: A Simulation Study

The decarbonisation of heavy-duty transport requires powertrains that meet stringent efficiency, weight, packaging and refuelling constraints. This thesis considers an energy pathway in which renewable electricity is used offboard to produce hydrogen, which is converted to ammonia for storage and distribution. Onboard the vehicle, ammonia is reconverted to hydrogen to supply a proton exchange membrane fuel cell (PEMFC).
Ammonia is an attractive hydrogen carrier because of its high hydrogen density, carbon-free composition and established infrastructure. However, ammonia electrolysis remains at a relatively low technology readiness level and has received limited system-level assessment for onboard heavy-duty vehicle applications, where net power, parasitic loads, heat and water management, hydrogen purity, stack sizing and packaging are important.
A comparative system-level feasibility study is presented for three onboard ammonia-to-hydrogen pathways: aqueous alkaline electrolysis, anhydrous liquid ammonia electrolysis and solid-acid electrochemical cells (SAECs), each integrated with a PEMFC. First-order mass and energy balance models are used under representative steady-state operating conditions.
Aqueous alkaline electrolysis achieves efficiencies up to 22.5%, with specific energy consumption of 10.9–20 kWh kg⁻¹ H₂, but is constrained by water-management penalties and parasitic loads. Anhydrous liquid ammonia electrolysis achieves 26–50% efficiency and 3.7–4.3 kWh kg⁻¹ H₂, reflecting simpler water management and better integration potential. SAECs achieve 12.2–47.7% efficiency and 2.1–6.0 kWh kg⁻¹ H₂, although stability and durability remain challenges.
The work provides a system-level feasibility framework for onboard ammonia electrolysis integrated with PEMFCs in heavy-duty vehicles. It defines the feasibility boundaries of the three pathways, identifies key integration requirements, and indicates liquid-phase electrolysis and low-current-density operation as promising directions for future development, including hybridisation with a medium-sized battery.