Also, note from this source that ammonia can be a reducing agent for 2*NOx->N2+O2 with a proper catalyst, with some base metal catalysts working in the 450C to 800C range. Since an ammonia fuel cell would obviously have an ongoing supply of ammonia for that reducing reaction, it seems like good NOx control ought to be possible for the combustion of the exhaust hydrogen to drive the cracker.

The temperature for the base metal catalyst seems to support the 2*NH3->N2+3*H2 cracking approach I noted above for an alkaline fuel cell that works well in the 500C range ~ the gas over the catalyst would already by in the right temperature range.

A lot of this is that hydrogen fuel cells have been pursued for quite a long while, and the push to develop the technologies for ammonia as an easier to control and manage hydrogen carrier seems to be substantially more recent.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.