An in-depth study of the potential and challenges of ammonia and hydrogen as clean, zero-emission marine fuels
The global shipping industry, responsible for about 3% of global CO₂ emissions, is at the forefront of the energy transition debate. The growing demand for zero greenhouse gas emissions by mid-century has sparked a race for clean and sustainable fuels. Two of the leading contenders are green ammonia and green hydrogen.
But which is better suited for shipping? Below is a detailed analysis of the technical, economic, and environmental advantages and limitations of each option.
1. Green Ammonia: Promise with Structural Challenges
Ammonia (NH₃) can be produced with zero emissions by synthesizing green hydrogen with nitrogen from the air, using renewable electricity.
Advantages:
Zero CO₂ emissions during combustion.
Easier to store and transport: Liquefies at -33°C under atmospheric pressure—much easier than hydrogen at -253°C.
Existing infrastructure: Ammonia is already shipped globally in large quantities as fertilizer, facilitating supply chain development.
Challenges:
Toxicity: Highly toxic and corrosive, requiring strict safety protocols.
NOₓ emissions: Combustion can produce nitrogen oxides (NOₓ), harmful pollutants.
Engine compatibility: Engines must be redesigned or rely on specific technologies like solid oxide fuel cells (SOFCs).
2. Green Hydrogen: The Cleanest Energy with Practical Hurdles
Hydrogen, when produced by electrolysis using renewable electricity, is the cleanest fuel—its only byproduct is water.
Advantages:
Zero greenhouse gas and NOₓ emissions during use, especially in fuel cells.
High energy density by weight: About 120 MJ/kg, much higher than fossil fuels.
Challenges:
Storage & transport: Requires ultra-low temperatures or high-pressure tanks, making logistics difficult.
New infrastructure required: Ports are currently not equipped to handle hydrogen safely.
Technological maturity: Large-scale maritime hydrogen fuel cell systems are still in pilot phases.
3. Comparison Table
| Parameter | Ammonia | Hydrogen |
|---|---|---|
| CO₂ Emissions | Zero | Zero |
| NOₓ Emissions | High, needs control | Very low/none |
| Safety | Toxic, corrosive | Explosive, but non-toxic |
| Energy Density (by volume) | Medium | Very low |
| Existing Infrastructure | Yes (ports, logistics) | No (needs full development) |
| Technological Readiness | Emerging | Early-stage |
4. Global Projects and Investments
Ammonia
Fortescue's "Green Pioneer": The world’s first dual-fuel ammonia-powered vessel received global recognition at the 2024 World Hydrogen Awards.
NYK Line: Set to carry out the world’s first truck-to-ship ammonia bunkering for its “A-Tug” in Yokohama Port.
COSCO Shipping & Fortescue: Partnering to develop a green ammonia fuel supply chain, targeting emission reduction in shipping.
Sweden–Belgium Green Shipping Corridor: Plans two Ro-Ro vessels running on ammonia by 2030, linking Sweden and Belgium.
Hydrogen
MF Hydra: The world’s first liquid hydrogen-powered ferry, cutting CO₂ emissions by up to 95% annually.
TotalEnergies in Chile: Applied for an environmental permit for a $16 billion green hydrogen and ammonia project, aiming to start by 2030.
Toyota: Warned time is running out to counter China's lead in hydrogen vehicles, underscoring the need for urgent global investments.
5. Conclusion: Complementarity, Not Competition
Green ammonia and green hydrogen are not necessarily competing solutions. Instead, they may suit different shipping segments:
Ammonia is better suited for deep-sea, long-haul shipping.
Hydrogen may be ideal for ferries, short sea shipping, and regions with abundant renewable electricity.
The path to decarbonizing maritime transport is complex and multifaceted. Both fuels can coexist—what's needed is coherent policy, economic incentives, and accelerated tech deployment.