There’s a major push now to find energy sources with smaller carbon footprints. The maritime shipping industry, according to IEEE Spectrum, is going towards ammonia. Burning ammonia produces no CO2 and it isn’t hard to make. It doesn’t require special storage techniques as hydrogen does and it has ten times the energy density of a modern lithium-ion battery.
You can burn ammonia for internal combustion or use it in a fuel cell. However, there are two problems. First, no ships are currently using the fuel and second most ammonia today is made using a very carbon-intensive process. However it is possible to create “green” ammonia, and projects in Finland, Germany, and Norway are on schedule to start using ammonia-powered ships over the next couple of years.