electrochemistry - Wattage to produce 6L of air from Water in less than a second?

So I understand the question is probably vague to a scientist, but this is all the specifics I could mustard up with my non-scientific background.

So I understand the basics of the process and have used it occationally in a garage environment to fiddle around, but never really thought about the applications until a particular Indiegogo campaign claimed to have created artificial gills small enough to hold in your mouth and generating 45 minutes of breathable air.
The campaign have gotten a wide spread of media attention and it got me thinking, how much wattage would be required to produce 6L of air over the course of a second which happens to be a rough average of a adults lung capacity.

I understand that submarines use this process to create breathable air, but as someone mentioned they have a nuclear reactor onboard and "it would not be wise to attach that to your face".

Would shortening a Lithium Ion/Polymer battery be sufficient to create such a quick reaction? Or are we talking megawatts in order to produce such a volume of air in that time span?

Update to the numbers used:

Pointed out by @DavePhD, you don't use 6L per breath, rather 6L on average per minute.
Taking into account that this would be a physical exercise under water, you'd normally use anything between 14-17L per minute, on average 16L.

Also noted is that I should have used P instead of the term wattage, thanks @Loong