H2O Splitter Scuba Tanks
Simply split the hydrogen and oxygen and have two useful products for under water use. You can breath the oxygen created from the splitting of the H2O and use the hydrogen as a propellent. Normally we compress the oxygen in tanks and then dive. But, with the chemicals added in on extra tank that takes in the water and splits it into oxygen and hydrogen you can stay under water a much longer time. It might be better for deeper diving as well.