I’m imagining a ship with a hole in it and a piece of fuel at the backside where the particles hit. It would slow you down first since you’re tethered to the particles, then the explosion would push you forward.
The issue is that the energy for that explosion comes from the slowing down of your ship, so it doesn’t work.
The energy that comes from a mass-energy conversion greatly exceeds kinetic energy losses.
For the same reason that the power of an atomic bomb does not depend on how fast you smash the sections together - it depends on how much mass is converted to energy in the resulting reaction.
The issue is that the energy for that explosion comes from the slowing down of your ship, so it doesn’t work.