Pure hydrogen has some handling difficulties which might be solved by binding it to carbon (eg in Methane: CH_4), or to nitrogen (eg in Ammonia: NH_3).

Ammonia production has as an advantage that nitrogen is available in large quantities in the earth's atmosphere (78%), and ammonia production and usage can therefore _theoretically_ be carbon-neutral (and in fact not involve carbon at all, ideally)

Methane production has as an advantage that you can produce it using atmospheric carbon capture (pulling CO_2 from the air), which means it could theoretically contribute to reduction of greenhouse gasses. A downside of atmospheric carbon capture is that earth atmosphere CO_2 is fairly low (0.04%) .

(note: Atmospheric CO_2 capture is also proposed for Mars ISRU (In-Situ resource utilization), which is one reason why SpaceX is using methane engines for its upcoming generation of (mars) rockets. There's some synergies / extra investments to be had in working on CO2 capture technologies)

(note 2: Current modern methane and ammonia production/delivery tend to use fossil hydrocarbons as the hydrogen donor, rather than water electrolysis https://en.wikipedia.org/wiki/Ammonia_production#Modern_ammo... )