Introduction to Reliable Hydrogen Transport
As the world shifts toward a low-carbon future, hydrogen is emerging as a shining star among clean energy sources. Yet, realizing hydrogen’s complete potential will depend on one major hurdle: cost-effective, scalable hydrogen delivery. Compression and liquefaction are solutions but have limitations, particularly over long distances. That’s where chemical hydrogen carriers come in.
There are two frontrunners in the quest for a transport medium, and they are ammonia (NH₃) and liquid organic hydrogen carriers (LOHCs)—both of which have the potential to transport hydrogen safely and cost-effectively. But which has the upper hand when it comes to the world of hydrogen logistics?
In this blog, we take a look at how these carriers’ function and look at the pros and cons.
Why is transporting hydrogen challenging?
The energy content of hydrogen at normal temperature and pressure is highest; it is the highest energy volume source that does not have to be derived from hydrocarbons, but the lower ambient temperature density results in a low specific energy, and therefore, the storage and transport of hydrogen as a fuel are a major technical challenge. Overcoming that, hydrogen needs to be
- Solid (high-pressure tanks)
- Cryogenic temperatures are achieved with liquefied (below -253°C)
- Transformed into carriers (ammonia or LOHCs)
What are hydrogen carriers?
Hydrogen carriers are substances to which hydrogen is chemically attached for safer, more convenient storage and transportation. The hydrogen is then dehydrogenated—liberated—at the point of use.
Ammonia (NH₃) and LOHCs, as among the carriers, have been under intense focus because of their high-density hydrogen content and easy integration with the present infrastructure.
Why Choose Ammonia?
Ammonia, a widely used industrial chemical, offers various advantages due to its global logistics network. It contains 17.6% hydrogen by weight and can be liquefied at -33°C, making it more practical than liquefied hydrogen at -253°C.
Advantages of Using Ammonia as a Hydrogen Carrier
1. Peak Hydrogen Density
The weight percentage of hydrogen present in ammonia is 17.6%. This value is greater than that of liquid hydrogen. Additionally, 1 liter of liquid ammonia contains 50% more hydrogen than a liter of liquid H₂.
2. Existing Framework
Unlike hydrogen, ammonia already has a global network of infrastructure and commerce. Its widespread use in ports, storage, and shipping supports over 200 million tons of ammonia production annually, mainly for fertilizer use.
3. Relative Ease of Liquefaction
As compared to hydrogen, ammonia has an easier liquefaction process, with hydrogen needing -253°C while ammonia just needs -33°C.
4. Absence of Carbon Emissions
The only hydrogen amphora that can be produced from green ammonia is via renewable energy-powered electrolysis, giving it emission-free capability during temperature shifts.
5. Multi-Purpose Application
Ammonia can serve varied purposes, such as
- Intact council fuel for potently powered cells
- Ammonia-fed burner power plants
- Fertilizers and other chemicals
Challenges associated with ammonia in the role of Hydrogen Carrier
Ammonia has a few challenges to overcome:
- Safety concerns: Ammonia is toxic and requires special measures for handling.
- Energy Dehydrogenation: Gaining hydrogen requires energy (Cracking at 400-600 °C)
- Nitrogen Emissions: NOx can be emitted during combustion but is less common thanks to modern catalysts.
What are LOHCs?
It is a class of compounds whose hydrogen can be absorbed and released by them chemically.
Compounds like dibenzyl toluene or methylcyclohexane are LOHCs too. Since the processes of hydrogenation and dehydrogenation are reversible, LOHCs can be reused and offer adaptability.
The LOHC compound has a hydrogen storage capacity of ±7.19 wt% % and is a liquid at room temperature (m.p. 6.47 °C). (44, 45)
Advantages of Using LOHCs as Hydrogen Carriers
- High Safety: Stable, non-toxic, and non-explosive.
- Existing Infrastructure: Compatible with current oil and chemical transport systems.
- Reversible Storage: Hydrogen can be repeatedly loaded and released without carrier degradation.
- No Boil-Off Losses: Ideal for long-term storage.
- High Hydrogen Density: Comparable to high-pressure gas without extreme conditions.
- Long-Term Storage: Minimal losses over time.
- Flexible Logistics: Hydrogen can be stored and released at different locations.
- Eco-Friendly: Reusable over many cycles, reducing waste.
Challenges of Using LOHCs as Hydrogen Carriers
- High Energy Requirement: Hydrogen release (dehydrogenation) often needs high temperatures and significant energy input.
- Catalyst Dependence: Efficient hydrogenation and dehydrogenation require expensive catalysts, often based on precious metals.
- Slow Reaction Kinetics: Hydrogen loading and unloading can be relatively slow, impacting system efficiency.
- Carrier Degradation: Over many cycles, some LOHCs degrade, requiring purification or replacement.
- Hydrogen Purity: Released hydrogen may contain impurities that need further purification for fuel cell use.
- System Complexity: LOHC systems involve additional equipment for heating, catalyst handling, and purification, increasing complexity and cost.
- Initial Cost: High upfront investment for developing LOHC infrastructure and plants.
Ammonia vs. LOHCs: A Quick Comparison
| Form | Ammonia | LOHCs |
| Form | Chemical compound (NH₃) | Hydrogen chemically bonded to a carrier |
| Hydrogen Content | High by weight | Moderate by weight |
| Toxicity | Toxic and hazardous | Low toxicity |
| Infrastructure | Established globally | Can use existing fuel infrastructure |
| Hydrogen Release | Decomposition required (energy-intensive) | Requires heating (energy-intensive) |
| Storage Conditions | Stored as liquid under mild pressure | Stored in liquid form under ambient conditions |
| Transport | Existing ammonia transport systems | Compatible with oil transport systems |
Which Carrier Has the Edge?
There’s no one-size-fits-all answer. Ammonia is ideal for large-scale, long-distance hydrogen shipping, especially across oceans. Its established infrastructure and high hydrogen density make it a leading candidate for global hydrogen trade.
On the other hand, LOHCs are better suited for distributed, regional transport where safety and compatibility with existing fuel networks are paramount. Their non-toxic nature makes them attractive for urban and consumer-level hydrogen use.
Conclusion: Ammonia vs. LOHCs—Picking the Right Hydrogen Carrier
As the hydrogen economy grows, both ammonia and LOHCs offer smart solutions for hydrogen storage and transport. Ammonia excels in large-scale, long-distance shipping thanks to its high hydrogen density and established infrastructure. LOHCs, with their safety, reusability, and compatibility with existing fuel systems, are better suited for regional and decentralized transport.
Each carrier has its strengths depending on the application. Together, they are key to unlocking a scalable, efficient, and clean hydrogen future.
