I've been trying to find some thermodynamic explanation for this...

I've been trying to find some thermodynamic explanation for this energy charge, but understanding (and please correct me) is that it works at a atomic level and perhaps the equal and opposite reaction is so minute at this level that it is undetectable. But my guess would be some sort of rearrangement of H20, c02 and 02 molecules in contact with the graphene that then leads to a storage of the charge and release of hydrogen, oxygen, carbon or some molecule arrangement. Much like photosynthesis. This would be the holy grail though, reproduced photosynthesis. Neil degrass Tyson says that if we can unlock the process of photosynthesis, it would lead to a new industrial revolution. Just food for thought.