Research seems to be ongoing, but it seems that direct ammonia fuel cells may be high temperature. I came across a description of a "moderate" temperature approach, where that implies ~500C, with ammonia cracked to H2 and N2, used in an alkaline fuel cell, which has good rejection of unprocessed traces of ammonia, with the exhaust gas burned to heat the cracker.

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