One quick info.
For a propellant, the most important value is the Isp, the specific impulse. This value determines how much pounds thrust you get out of 1 pound of this Propellant(usually the fuel and the oxidizer, since different combinations result in different reaction values) per second. Also, multiply by g, and you get the aproximate exhaust velocity.
(Isp = F / ( dm/dt * g) = vexhaust / g , g=9.81 m/s2)
Most solid propellants for model rocketry are in range of 200-300 Isp, liquid Hydrogen+ Oxigen is in the range of about 500(nearly the upper limits of chemical drives), and electric ion drives ar able to produce an Isp between 1000 and 20000 "Seconds".
The present problem with electric drive is you need low tens of kilowatts to produce ~1N of thrust. (=Big, heavy reactors or long burntimes on solar power neded)
In general, for maximum thrust, you need a very light and fastmoving endproduct. Therefore, a liquid metal COULD make sense if its endproducts have these qualities. Usually metals are very dense, but since the group "metal" is only classified as having a "metallic" binding, there
could be an metallic element with the properties of water.
But since chemical propulsion is very inefficient, it would probably only be a reactant for the reactor, generating energy für the ion drive. There is no way to generate the amount of thrust seen on screen with ANY chemical reaction. But when using one pound of electrons in an actual present ion drive, you get up to 20.000 pounds of thrust.
Image of a running ion drive in the MIT lab. Looks familiar, doesn't it?
A minute's thought suggests that the very idea of this is stupid. A more detailed examination raises the possibility that it might be an answer to the question "how could the Germans win the war after the US gets involved?" - Captain Seafort, in a thread proposing a 1942 'D-Day' in Quiberon Bay
I do archery skeet. With a Trebuchet.