Protodermis was indeed created by the GBs before the discovery of EP or any plans for Mata Nui robot. It should be mentioned that this piece of information is one of those internally contradictory facts which have many sources telling us different things. But the interpretation others have put forward here seems to be the most consistent one (even though I personally think there are other, more believable versions, but what can we do…).
Yes! But let’s backtrack a little bit. First you asked if it could be used as fuel. It already is. The protodermis was mined on Mata Nui and used as a source of energy:
The mysterious substance had been mined on Mata Nui for years, used as a source of power.
-BCh2
Other indicators of protodermis containing energy is the manufacturing process of Kanoka disks and Kanohi masks.
Perhaps even more importantly the entire population of the Matoran universe is made out of protodermis and runs on protodermis-derived energy. This energy had several names in the story, such as internal, personal, or physical energy (I call it physical energy for short).
So to sum it up the “energy of protodermis” is essentially identical to the energy contained in Kanoka, Kanohi and beings. Speaking of beings, many of them have non-elemental electricity powers (Axonn or Suukorak for example), which draw upon this energy - therefore the protodermis can indeed produce electricity albeit indirectly. It first starts out as this “energy of protodermis” which is not electricity in itself:
Q: A Toa of electricity could restore the energy of a Matoran who lost his mask and maintain this energy until the Matoran has a new mask?
A: No. What they get from a mask is not simply electrical energy.