Shipping hydrogen across an ocean is a volume problem: liquid H₂ needs −253 °C tanks and still boils off in transit. Converting it to ammonia (NH₃) via Haber–Bosch lets it travel at −33 °C in ordinary pressurised tankers — the same ships and ports used for LPG today — at roughly 1.7× the volumetric energy density of liquid H₂. The catch is that both the forward synthesis and the reverse cracking step consume energy and never reach 100% conversion.
N₂ + 3H₂ ⇌ 2NH₃ (exothermic)
Kp(T) favors NH₃ as T↓, favors NH₃ as P↑
2NH₃ → N₂ + 3H₂ (endothermic, needs heat + catalyst)
η_round-trip = (1 − loss_synth) × (1 − loss_crack)
- Synthesis temperature — Haber–Bosch is exothermic, so equilibrium conversion rises as temperature falls (Le Chatelier), but reaction rate collapses below ~350 °C, so real plants trade a lower per-pass yield for a usable rate.
- Synthesis pressure — the reaction shrinks 4 moles of gas into 2, so higher pressure pushes equilibrium toward NH₃; today's plants pay for that in compressor energy, shown as synthesis loss.
- Cracking temperature — reversing the reaction at the destination is endothermic and needs a hot catalyst bed; running it too cool leaves NH₃ undecomposed, running it hot burns more of the delivered hydrogen just to supply the heat.
- NH₃ vs liquid-H₂ route — the reference bar shows liquefaction's own ~30% energy penalty with no reconversion step, so you can compare the two shipping strategies directly at whatever settings you choose.
Real-world relevance: this two-step conversion is why current green-hydrogen export projects (Australia, Middle East, Namibia) plan to ship ammonia rather than liquid H₂ — even though every extra chemical step "spends" some of the very energy the hydrogen was made to carry.