Fuel Cells

• A good way to avoid NOx is to avoid combustion, and fuel cells deliver electricity from non combustion reactions moderated by catalysts. There are fuels cells which range from relatively cool to very high temperatures, liquid metal oxides.
• The ideal fuel cell configuration is to feed pure Hydrogen (H2) and pure Oxygen (O2) to a fuel cell, to obtain electricity and pure water (H2O). Energy conversion efficiencies of up to 60% can be achieved, and this is now the preferred power source for submarines, as (unlike nuclear reactors) it minimises leakage of heat that might be detectable.
• The technology is not yet suitable for commercial use in commercial shipping, but research and development is occurring.

INDEPTH
Variations may be possible to develop fuel cells for use in ships:

• Air can be used instead of pure O2. But with the complication of needing to use 5 times the gas volumes;
• Methanol can be used instead of Hydrogen. But with the complication of needing to reform it first.
• Hydrocarbons can be used instead of methanol, but with the complication of higher temperature reactions and more difficult catalysts,

There may come a time when there are technologies to convert heavy fuels to electricity, water and CO2, with no other harmful emissions, but there do not yet seem to be grounds for assuming that this will be a viable future technology.

Perhaps more likely, with the appearance of the “hydrogen economy” and the “oil end game” will be hydrogen fuelled ships. Hydrogen is a good energy carrier, with high energy densities for its weight, and it will work with fuel cells as well as internal combustion engines. But it is far from clear how best ships should be equipped to carry hydrogen bunkers, nor what the energy conversion technology should be. So far, we can only speculate.