What I mean by that, is instead of using the fuel cell to produce electricity, is there a product where the fuel cell is used to split water and half the gas is used for the ICE and the other goes back into the fuel cell to power it? Is there a product like that I can buy?
Actually, a fuel cell won't produce hydrogen. Electrolysis will.
So, what you are suggesting is using hydrogen to power a fuel cell and the obtained electricity for electrolysis to obtain hydrogen.
Now, the problem is that if you divert half of the obtained hydrogen to an internal combustion engine, only half of the energy remains in the rest. So, every cycle of this machine will mean you have less and less hydrogen.
The system will work only if you have a big hydrogen tank somewhere. The tank will eventually be depleted. Now, if you have a big hydrogen tank, why don't you directly power an internal combustion engine by using the hydrogen, or better yet, power the fuel cell and use all of the electricity in electric motors, without trying to waste the electricity in electrolysis?
No. The energy you get from burning hydrogen cannot possibly be more than the energy you spend splitting it. Perpetual motion machines are physically impossible.
Also, when you burn fuel in an ICE, it will at best recover about 35% of that energy as motion, driving the wheels and/or a generator. The remainder is lost (to friction, exhaust gas velocity etc.)
There have been a few hydrogen ICEs (BMW had a few 7-series converted as test vehicles), they all used high-pressure gas bottles or a metal hydride tank as storage.