This is a demonstration of electrolysis. The reaction produces hydrogen and oxygen which makes a potent gas mixture which its production rate is dependent on the flowing current and surface area of the anode and cathode. Now the thing to balance it against thermodynamics, is the battery which is also using electrolysis to make for an electrical current to make this reaction. The missing step is to making a feed back to keep the reaction going without the aid of the battery. Otherwise, you are just using the battery alone with extra steps and more waste. That gas explosion has to be utilized to drive an alternator to maintain the current. You could drive with permeant magnet motors to use the excess directly from the alternator and capture energy from the reverse emf to maintain the reaction or drive a crankshaft with the gas. As in many other demonstrations, the energy left over in ideal conditions is still very little. It will run into the same stumble as EVs.