Hydrogen and Fuel Cells: Fighting the Storage Physics

7 min read

What you'll take away Explain why hydrogen's storage physics confines it to short-sea niches for now, and distinguish the fuel-cell and combustion routes to using it on board.

Judge fuels by energy per kilogram and hydrogen wins the course outright: roughly 120 MJ/kg, three times fuel oil. Judge by energy per cubic metre of ship and it finishes last among the chemical fuels. Both facts are the same molecule seen from different axes of lesson 2's framework, and the tension between them decides everything about hydrogen at sea.

The storage physics

Hydrogen liquefies at about −253 °C: twenty degrees above absolute zero, some ninety degrees colder than LNG. Even then the liquid is feather-light, around 71 kg/m³, so a cubic metre of liquid hydrogen holds roughly a quarter of the energy in a cubic metre of distillate, before the tank itself is counted, and hydrogen tanks are formidable: multi-layer insulation, careful thermal design against boil-off, and generous surrounding space. The alternative, compressed gas at 350 or 700 bar, trades the cold for thick-walled cylinders and does not beat the liquid on volume. There is no third option; the physics is the physics.

Materials feel hydrogen too. The smallest molecule in nature diffuses into steels and degrades their toughness, hydrogen embrittlement, which rules out many high-strength grades and puts welds under special scrutiny. Add a flammability range in air of roughly 4–75% and an ignition energy so low that a static spark suffices, and you have a fuel that demands leak-tightness and ventilation engineering of a different order. One mercy: hydrogen is fourteen times lighter than air and rises, so unlike LPG it does not pool in bilges: design channels it up and out. ABS's whitepaper on hydrogen as marine fuel (open) covers the production, storage and safety picture end to end.

Fuel cells or combustion

Once aboard, hydrogen can make power two ways. Internal combustion is the rugged route: engine makers adapt known machinery, tolerating hydrogen's quirks in exchange for maritime durability, with NOx as the main exhaust concern. Fuel cells, PEM cells above all, are the elegant route: electrochemical conversion straight to electricity, higher efficiency, no combustion by-products, near-silent. Their challenges are cost per kilowatt, stack lifetime in salt air and vibration, sensitivity to fuel purity, and load-following on a seaway. The pragmatic near-term pattern pairs fuel cells with batteries: the battery absorbs transients, the cell runs steady. Lloyd's Register's Fuel for thought hydrogen report (free after registration) surveys both routes with case studies.

A third architecture deserves attention because it may be how deep-sea shipping actually uses hydrogen: make it on board. Bunker a manageable liquid, methanol, or ammonia, and reform or crack it to hydrogen on demand, feeding cells or engines while the tank holds something a port can supply. Hydrogen then exists on the ship only in pipe-sized quantities. Lloyd's Register has published dedicated guidance notes for onboard hydrogen generation (free after registration) covering exactly these reforming and cracking plants.

Three ways to turn hydrogen into propulsion 1 · Combustion route Liquid hydrogen −253 °C, insulated tank Internal combustion rugged; NOx to treat Shaft power known machinery 2 · Fuel-cell route Liquid hydrogen −253 °C, insulated tank PEM fuel cell + battery no combustion, efficient Electric propulsion near-silent 3 · Onboard generation from a carrier fuel Methanol or ammonia stored as a mild liquid Reformer or cracker hydrogen made on demand Fuel cell or engine H2 only in pipe volumes
The first two routes both pay the −253 °C storage bill and differ only in the converter; the third refuses that bill by bunkering a manageable liquid and making hydrogen at the point of use. Which route a ship can afford is decided in the left-hand column, not the right.

Where it fits

Run the framework honestly. Well-to-wake: superb if the hydrogen is green, poor if grey: production colour decides, as with ammonia and methanol. Availability: thin, and liquid-hydrogen bunkering is in its infancy. Cost: high on every line. Readiness: rules and reference designs are forming; the fleet is small. Hence the 53 ships on order from lesson 1: ferries, harbour craft and offshore support vessels on short, fixed routes where frequent bunkering shrinks the storage problem and one committed port can anchor supply.

That is not a dismissal. Short-sea is where LNG started, and hydrogen's end-state, a carbon-free molecule through a silent fuel cell, remains the cleanest picture in this course. Fuel cells themselves are also a bigger story than hydrogen: the same stacks can run on reformed methanol or cracked ammonia, so the technology earns its sea time even where pure hydrogen bunkering never arrives. But for deep-sea tonnage today, hydrogen is less a fuel choice than an ingredient: the feedstock of the e-fuels in lesson 9, and the payload inside the ammonia of lesson 6. The molecule will cross oceans; the open question is which chemical overcoat it wears.

Check yourself

1. Hydrogen's central paradox as a marine fuel is that it is…
2. Hydrogen embrittlement refers to…
3. Compared with burning hydrogen in an engine, a fuel cell…
4. Why does onboard hydrogen generation from a carrier fuel appeal to designers?
5. The realistic near-term home for hydrogen propulsion is…
6. Liquid hydrogen must be stored at approximately what temperature?
°C
7. Which of these are real handling challenges specific to hydrogen?

Select all that apply.

8. Hydrogen produced from natural gas without carbon capture is a low-emission fuel on a well-to-wake basis.