There was a lot of hype $10$ to $15$ years ago over the hydrogen economy. It was of course rather odd that anyone could take this seriously. How much free hydrogen gas is available? Answer: virtually none. The problem is that you have to either put electrical energy into water to split it into $H_2$ and $O_2$, or if you chemically condition methane $CH_4$ you may strip the hydrogen atoms free of the carbon, but you still have that carbon. As a result hydrogen is either an energy storage system, or a way of banking another form of energy (fossil fuels etc) in a way that lacks the carbon.
Antimatter is a similar issue, though at much higher energy. There is no freely available antimatter in the universe, at least as far as we know. With accelerators the amount of energy required to generate antimatter is far larger than the mass-energy contained in it. The energy utility in generating antimatter is highly negative at this point.