Creating the Star Wars Breather using Chemistry?

So, if there are any Star Wars fans out there, you may be familiar with the breather that is in the pre-sequals of Star Wars.

A very useful tool, but the question is if it is possible to develop some device that is similar. It would seem pretty straightforward, so I did some research on how this would be possible.

First, we have to assume that the user is underwater. The way this breather could be developed is by having a small container that attatches to the breather. This contains the mechanism that converts the water into oxygen. This can easily be done with the electrolysis of water. However, we want to be environmentally friendly with this device. Therefore, one way we can put the water back into the body of water that the user is in is by using the mask that the user has on their mouth and take the carbon dioxide that we breath out, split the carbon dioxide into carbon and O2, and then recombine the Oxygen and hydrogen that will be stored in the device when the water is split into its components.

It's easier said than done, but I think it would be a good way to develop a device as such. I haven't done any calculations at all, so maybe provide some information on this if you want. Does something like this already exist?